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1.  Mortality due to coronary heart disease and kidney disease among middle-aged and elderly men and women with gout in the Singapore Chinese Health Study 
Annals of the Rheumatic Diseases  2011;71(6):924-928.
Whether the link between gout and mortality is causal or confounded by lifestyle factors or comorbidities remains unclear. Studies in Asia are warranted due to the rapid modernisation of the locale and ageing of the population.
The association between gout and mortality was examined in a prospective cohort, the Singapore Chinese Health Study, comprising 63 257 Singapore Chinese individuals, aged 45–74 years during the enrolment period of 1993–8. All enrollees were interviewed in person on lifestyle factors, current diet and medical histories. All surviving cohort members were contacted by telephone during 1999–2004 to update selected exposure and medical histories (follow-up I interview), including the history of physician-diagnosed gout. Cause-specific mortality in the cohort was identified via record linkage with the nationwide death registry, up to 31 December 2009.
Out of 52 322 participants in the follow-up I interview, 2117 (4.1%) self-reported a history of physician-diagnosed gout, with a mean age at diagnosis of 54.7 years. After a mean follow-up period of 8.1 years, there were 6660 deaths. Relative to non-gout subjects, subjects with gout had a higher risk of death (HR 1.18; 95% CI 1.06 to 1.32), and specifi cally from death due to coronary heart disease (CHD) (HR 1.38, 95% CI 1.10 to 1.73) and kidney disease (HR 5.81, 95% CI 3.61 to 9.37). All gout–mortality risk associations were present in both genders but the risk estimates appeared higher for women.
Gout is an independent risk factor for mortality, and specifically for death due to CHD and kidney disease.
PMCID: PMC3400339  PMID: 22172492
2.  Plasma S-adenosylmethionine, DNMT polymorphisms, and peripheral blood LINE-1 methylation among healthy Chinese adults in Singapore 
BMC Cancer  2013;13:389.
Global hypomethylation of repetitive DNA sequences is believed to occur early in tumorigenesis. There is a great interest in identifying factors that contribute to global DNA hypomethylation and associated cancer risk. We tested the hypothesis that plasma S-adenosylmethionine (SAM) level alone or in combination with genetic variation in DNA methyltransferases (DNMT1, DNMT3A and DNMT3B) was associated with global DNA methylation extent at long interspersed nucleotide element-1 (LINE-1) sequences.
Plasma SAM level and LINE-1 DNA methylation index were measured using stored blood samples collected from 440 healthy Singaporean Chinese adults during 1994-1999. Genetic polymorphisms of 13 loci in DNMT1, DNMT3A and DNMT3B were determined.
LINE-1 methylation index was significantly higher in men than in women (p = 0.001). LINE-1 methylation index was positively associated with plasma SAM levels (p ≤ 0.01), with a plateau at approximately 78% of LINE-1 methylation index (55 nmol/L plasma SAM) in men and 77% methylation index (50 nmol/L plasma SAM) in women. In men only, the T allele of DNMT1 rs21124724 was associated with a statistically significantly higher LINE-1 methylation index (ptrend = 0.001). The DNMT1 rs2114724 genotype modified the association between plasma SAM and LINE-1 methylation index at low levels of plasma SAM in men.
Circulating SAM level was associated with LINE-1 methylation status among healthy Chinese adults. The DNMT1 genetic polymorphism may exert a modifying effect on the association between SAM and LINE-1 methylation status in men, especially when plasma SAM level is low. Our findings support a link between plasma SAM and global DNA methylation status at LINE-1 sequences.
PMCID: PMC3765398  PMID: 23957506
3.  Serum free estradiol and estrogen receptor-α mediated activity are related to decreased incident hip fractures in older women 
Bone  2012;50(6):1311-1316.
There is paucity of data from Asian women on the association between serum estrogens and osteoporotic hip fracture risk. We conducted a case-control study nested within a population-based prospective cohort, The Singapore Chinese Health Study, to evaluate serum estrogens levels, ERα-mediated estrogenic activity and hip fracture risk in postmenopausal Asian women. Among 35,298 women who were recruited between 1993 and 1998, 15,410 women donated blood for research between 1999 and 2004. From this subcohort, we identified 140 cases who subsequently suffered hip fracture after blood donation, and 278 age-matched controls. Serum levels of total estrone, estradiol and sex hormone binding globulin levels were measured in a blinded fashion among cases and controls. ERα-mediated estrogenic activity of serum samples was quantified using a sensitive ERα-driven cell bioassay. Women with hip fracture had lower serum estrogens than control women. Compared to the lowest quintile, women in the highest quintile of free estradiol exhibited a statistically significant 57% reduction in risk of hip fracture (95% confidence interval (CI), 6%–80%), with a dose-dependent relationship (p for trend = 0.021). High levels of ERα-mediated estrogenic activity was also associated with decreased risk of hip fracture (p for trend=0.048). Overall, women with relatively high levels of both free estradiol and ERα-mediated estrogenic activity had a 55% reduction in hip fracture risk (95% CI, 17%–76%) compared to women with low levels of both. High levels of free estradiol and ERα-mediated estrogen activity in sera were associated with reduced hip fracture risk in Chinese postmenopausal women.
PMCID: PMC3353105  PMID: 22445734
Estrogens; Hip Fracture; ERα-mediated estrogenic activity; Population-based; Asian women
4.  Genetic variation in folylpolyglutamate synthase and gamma-glutamyl hydrolase and plasma homocysteine levels in the Singapore Chinese Health Study 
The enzymes folylpolyglutamate synthase (FPGS) and gamma-glutamyl hydrolase (GGH) are essential for determining intracellular folate availability for one-carbon metabolism (OCM) pathways. FPGS adds glutamyl groups to the folate molecule, thereby converting folate into the preferred substrate for several enzymes in OCM pathways. GGH removes glutamyl groups, allowing folate metabolites to leave the cell. The purpose of this study was to evaluate whether single nucleotide polymorphisms (SNPs) in the FPGS and GGH genes influence measured plasma homocysteine levels. Study participants were a sub-cohort (n = 482) from the Singapore Chinese Health Study. SNPs were selected using HapMap tagSNPs and SNPs previously reported in the scientific literature. Multiple linear regression was used to evaluate the association between individual SNPs and plasma homocysteine levels. Two FPGS (rs10106, rs1098774) and 9 GGH (rs719235, rs1031552, rs1800909, rs3758149, rs3780126, rs3824333, rs4617146, rs11545076, rs11545078) SNPs were included in the final analysis. Neither of the FPGS SNPs, but three GGH SNPs were associated with plasma homocysteine levels: rs11545076 (p=0.001), rs1800909 (p=0.02), and rs3758149 (p = 0.006). Only one (rs11545076) remained statistically significant after adjusting for multiple comparisons. This study suggests that GGH SNPs, rs11545076, rs1800909, and rs3758149, may have functional relevance and result in alterations in plasma homocysteine levels. Since this is one of the first studies to assess FPGS and GGH genetic variants in relation to plasma homocysteine, further research is needed to confirm these findings and characterize the functional effects of these variants.
PMCID: PMC3253895  PMID: 22018726
FPGS; GGH; Folate; Homocysteine; SNP
5.  Aromatase (CYP19) promoter gene polymorphism and risk of non-viral hepatitis-related hepatocellular carcinoma 
Cancer  2011;117(15):3383-3392.
Experimental studies suggest that sex hormones may induce or promote the development of hepatocellular carcinoma (HCC). Androgens are converted to estrogens by the CYP19 gene product, aromatase. Hepatic aromatase level and activity have been shown to be markedly elevated in HCC. Aromatase expression in liver tumors is driven by a promoter upstream of CYP19 exon I.6.
We first identified an A/C polymorphism in the exon I.6 promoter of the CYP19 gene. To determine whether allelic variants in the CYP19 I.6 promoter differ in their ability to drive gene expression, we carried out an in-vitro reporter gene assay. We then studied the association between this polymorphism and HCC risk in two complementary case-control studies: one in high-risk southern Guangxi, China, and another in low-risk US non-Asians of Los Angeles County.
Transcriptional activity was 60% higher for promoter vectors carrying the rs10459592 C allele compared to those carrying an A allele (p=0.007). In both study populations, among subjects negative for at-risk serologic markers of hepatitis B or C, there was a dose-dependent association between number of high activity C allele and risk of HCC (p for trend=0.014). Risk of HCC was significantly higher [odds ratio (OR) = 2.25, 95% confidence interval (CI) = 1.18–4.31] in subjects homozygous for the C allele compared to those homozygous for the A allele.
Our study provides epidemiologic evidence for the role of hepatic aromatization of androgen into estrogen in the development of non-viral hepatitis-related HCC.
PMCID: PMC3138892  PMID: 21319151
Aromatase enzyme; hepatocellular carcinoma; gene polymorphism; viral hepatitis; sex hormones
6.  Diabetes and Risk of Hip Fracture in the Singapore Chinese Health Study 
Diabetes Care  2010;33(8):1766-1770.
Asian populations are documenting rapid increases in the rates of diabetes and hip fracture, but there are no prospective data linking both diseases in Asian studies. We investigated this association among a cohort of Chinese in Singapore.
A prospective cohort of 63,257 Chinese in the Singapore Chinese Health Study, established between 1993 and 1998, was followed up for a mean duration of 12 years. Diabetes status was ascertained by baseline interviews, and incidence of hip fracture post-enrollment was identified through a nationwide hospital discharge database.
The risk of hip fracture, after adjustment for other risk factors, was almost double among people with diabetes compared with people without diabetes (relative risk 1.98, 95% CI 1.71–2.29). When stratified by BMI, the increase in risk of hip fracture among people with diabetes relative to people without diabetes was similar in all four strata. There was a very strong dose-dependent relationship between duration of diabetes and risk of hip fracture (P for trend <0.0001). Compared with people without diabetes, the relative risk (95% CI) among subjects with diabetes for <5 years at recruitment was 1.40 (1.08–1.82), and this risk increased to 2.66 (2.04–3.47) among individuals with diabetes for ≥15 years.
Asians with diabetes, like their Western counterparts, experience an increased risk of hip fracture. Early assessment for osteoporosis and increased fracture risk, as well as prevention of falls, should be part of the management of diabetes.
PMCID: PMC2909059  PMID: 20504896
7.  Gender-specific Associations Between Soy and Risk of Hip Fracture in the Singapore Chinese Health Study 
American Journal of Epidemiology  2009;170(7):901-909.
Although there is some epidemiologic evidence that soy may reduce risk of osteoporotic fracture in women, it is not known whether this risk reduction also occurs for men. The authors examined gender-specific associations between soy intake and hip fracture risk in the Singapore Chinese Health Study, a prospective cohort of 63,257 Chinese living in Singapore. At recruitment between 1993 and 1998, each subject was administered a food frequency questionnaire and questions on medical history and lifestyle factors. As of December 31, 2006, 276 incident cases of hip fracture in men and 692 cases in women were identified via linkage with hospital discharge databases. For both genders, hip fracture risk was positively associated with cigarette smoking and was inversely associated with body mass index. There was a statistically significant association of tofu equivalents, soy protein, and isoflavones with hip fracture risk among women but not among men. Compared with women in the lowest quartile of intakes for tofu equivalents (<49.4 g/day), soy protein (<2.7 g/day), and isoflavones (<5.8 mg/1,000 kcal/day), those in the second–fourth quartiles exhibited 21%–36% reductions in risk (all P < 0.036). Risk levels were comparable across the second, third, and fourth quartiles of soy intake categories.
PMCID: PMC2765361  PMID: 19720865
Asian Continental Ancestry Group; hip fractures; isoflavones; osteoporosis; soy foods
8.  Differential Effects of Black versus Green Tea on Risk of Parkinson's Disease in the Singapore Chinese Health Study 
American journal of epidemiology  2007;167(5):553-560.
Data from Asian populations on dietary and lifestyle factors associated with Parkinson's disease are sparse. In 1993-2005, the authors examined these factors in relation to Parkinson's disease in the Singapore Chinese Health Study, a prospective cohort of 63,257 Chinese men and women. Baseline data were collected through in-person interviews using structured questionnaires. All 157 incident Parkinson's disease cases were identified either through follow-up interviews or via linkage with hospital discharge databases and Parkinson's disease outpatient registries and were confirmed by review of medical records. Current versus never smokers exhibited a reduced risk of Parkinson's disease (relative risk = 0.29, 95% confidence interval: 0.16, 0.52). Total caffeine intake was inversely related to Parkinson's disease risk (p for trend = 0.002); the relative risk for the highest versus lowest quartile was 0.55 (95% confidence interval: 0.35, 0.88). Black tea, a caffeine-containing beverage, showed an inverse association with Parkinson's disease risk that was not confounded by total caffeine intake or tobacco smoking (p for trend = 0.0006; adjusted relative risk for the highest vs. lowest tertile of intake = 0.29, 95% confidence interval: 0.13, 0.67). Green tea drinking was unrelated to Parkinson's disease risk. Diet had no strong influence on risk. Ingredients of black tea other than caffeine appear to be responsible for the beverage's inverse association with Parkinson's disease.
PMCID: PMC2737529  PMID: 18156141
Asian continental ancestry group; coffee; food and beverages; Parkinson disease; Singapore; smoking; tea
9.  Sleep Duration and Coronary Heart Disease Mortality Among Chinese Adults in Singapore 
American journal of epidemiology  2008;168(12):1367-1373.
While some studies have found a positive association between both short and long sleep durations and cardiovascular disease (CVD), others have found an association only with a long or short sleep duration. In addition, there are limited data from non-Western populations on this topic. The authors examined the association between sleep duration and coronary heart disease (CHD) mortality among Chinese adults in Singapore (1993-2006), performing a prospective cohort study among 58,044 participants aged ≥45 years (55.9% women) without preexisting CVD. The main outcome of interest was CHD mortality (n = 1,416). The authors found both short and long sleep durations to be positively associated with CHD mortality, independent of smoking, alcohol intake, and body mass index. Compared with persons with a sleep duration of 7 hours (referent), the multivariable relative risk of CHD mortality for a sleep duration of ≤5 hours was 1.57 (95% confidence interval: 1.32, 1.88); for a sleep duration of ≥9 hours, it was 1.79 (95% confidence interval: 1.48, 2.17). This association persisted in subgroup analyses by sex sleep and body mass index. In a population-based cohort of Chinese adults from Singapore, sleep durations of ≤5 hours and ≥9 hours (versus 7 hours) were modestly associated with CHD mortality. These results suggest that duration may be an important marker for CVD.
PMCID: PMC2643470  PMID: 18952563
Asian continental ancestry group; cardiovascular diseases; coronary disease; mortality; Singapore; sleep
10.  Incense Use and Cardiovascular Mortality among Chinese in Singapore: The Singapore Chinese Health Study 
Environmental Health Perspectives  2014;122(12):1279-1284.
Background: Incense burning is common in many parts of the world. Although it is perceived that particulate matter from incense smoke is deleterious to health, there is no epidemiologic evidence linking domestic exposure to cardiovascular mortality.
Objective: We examined the association between exposure to incense burning and cardiovascular mortality in the Singapore Chinese Health Study.
Methods: We enrolled a total of 63,257 Singapore Chinese 45–74 years of age during 1993–1998. All participants were interviewed in person to collect information about lifestyle behaviors, including the practice of burning incense at home. We identified cardiovascular deaths via record linkage with the nationwide death registry through 31 December 2011.
Results: In this cohort, 76.9% were current incense users, and most of the current users (89.9%) had burned incense daily for ≥ 20 years. Relative to noncurrent users, current users had a 12% higher risk of cardiovascular mortality [multivariable adjusted hazard ratio (HR) = 1.12; 95% CI: 1.04, 1.20]. The HR was 1.19 (95% CI: 1.03, 1.37) for mortality due to stroke and 1.10 (95% CI: 1.00, 1.21) for mortality due to coronary heart disease. The association between current incense use and cardiovascular mortality appeared to be limited to participants without a history of cardiovascular disease at baseline (HR = 1.16; 95% CI: 1.07, 1.26) but not linked to those with a history (HR = 1.00; 95% CI: 0.86, 1.17). In addition, the association was stronger in never-smokers (HR = 1.12; 95% CI: 1.02, 1.23) and former smokers (HR = 1.19; 95% CI: 1.00, 1.42) than in current smokers (HR = 1.05; 95% CI: 0.91, 1.22).
Conclusions: Long-term exposure to incense burning in the home environment was associated with an increased risk of cardiovascular mortality in the study population.
Citation: Pan A, Clark ML, Ang LW, Yu MC, Yuan JM, Koh WP. 2014. Incense use and cardiovascular mortality among Chinese in Singapore: The Singapore Chinese Health Study. Environ Health Perspect 122:1279–1284;
PMCID: PMC4256695  PMID: 25127437
11.  Calcium intake increases risk of prostate cancer among Singapore Chinese 
Cancer research  2010;70(12):4941-4948.
Consumption of dairy products, the primary source of calcium in Western diets, has been found to be positively associated with prostate cancer. In an Asian diet, non-dairy foods are the major contributors of calcium. Thus, a study of dietary calcium and prostate cancer in Asians can better inform on whether calcium, as opposed to other dairy components is responsible for the dairy foods-prostate cancer association. We examined calcium intake and prostate cancer risk among 27,293 men of the Singapore Chinese Health Study that was established between 1993 and 1998. As of December 31, 2007, 298 incident prostate cancer cases had been diagnosed among the cohort members. Diet was assessed at baseline with a validated 165-item food frequency questionnaire. It is hypothesized that there is greater net absorption of calcium in smaller individuals. Therefore, the calcium-prostate cancer association was also assessed in stratified analyses by median body mass index (BMI). Vegetables were the largest contributor of daily calcium intake in the study population. Overall, we observed a modest, statistically nonsignificant 25% increase in prostate cancer risk for the 4th (median = 659 mg/day) versus 1st (median=211 mg/day) quartiles of calcium intake after adjustment for potential confounders. The association became considerably stronger and achieved statistical significance (hazard ratio=2.03; 95% confidence interval: 1.23, 3.34; P for trend=0.01) for men with below median (22.9 kg/m2) BMI. Dietary calcium may be a risk factor for prostate cancer even at relatively low intake.
PMCID: PMC4219618  PMID: 20516117
calcium; body mass index; insulin-like growth factor; prostate cancer; Singapore Chinese
12.  Hormone metabolism genes and mammographic density in Singapore Chinese women 
Female steroid hormone levels and exogenous hormone use influence breast cancer risk. We investigated the association between genetic variation in the hormone metabolism and signaling pathway and mammographic density (MD), a strong predictor of breast cancer risk.
We genotyped 161 SNPs in 15 hormone metabolism pathway gene regions and evaluated MD in 2,038 Singapore Chinese women. Linear regression analysis was used to investigate SNP-MD association. An overall pathway summary was obtained using the adaptive ranked truncated product test.
We did not find any of the individually tested SNPs to be associated with MD after a multiple testing correction. There was no evidence of an overall effect on MD of genetic variation in the hormone metabolism pathway.
In this cross-sectional study, genetic variation in hormone metabolism pathway was not associated with MD in Singapore Chinese women.
Consistent with existing data from Caucasian populations, polymorphisms in hormone pathway genes are not likely to be strong predictors of MD in Asian women.
PMCID: PMC4197055  PMID: 23429186
Hormone metabolism; polymorphism; mammographic density; Chinese
13.  Serum urate levels and consumption of common beverages and alcohol among Chinese in Singapore 
Arthritis care & research  2013;65(9):1432-1440.
Western studies suggest that beverages may affect serum urate (SU) levels but data from Asian populations are scarce. We evaluated the associations between beverages and SU levels in Singapore Chinese.
The study population consisted of 483 subjects from the Singapore Chinese Health Study cohort, aged 45-74 years, recruited between 1993 and 1998. Lifestyle factors, medical histories and diet were collected through in-person interviews. SU and other biomarkers were measured from blood collected between 1994 and 1996.
Mean age was 57.6 years and 44% were men. The geometric mean of SU was 321 μmol/L (range 157-719 μmol/L). Mean SU levels increased with alcohol consumption (P for trend = 0.024). The mean SU level of daily alcohol drinkers was 42.6 μmol/L higher than that of non-drinkers. Similarly, increasing frequency of green tea intake was associated with rising SU levels. The highest mean SU level was observed in daily green tea drinkers (difference of 25.0 μmol/L) relative to non-drinkers (P for trend = 0.009). Compared to non-drinkers, daily alcohol drinkers had an almost 5-fold increase in association with hyperuricaemia [odds ratio (OR) = 4.83; 95% confidence interval (CI) = 1.10-21.23) while daily green tea drinkers had a 2-fold increase in association with hyperuricaemia (OR=2.12, 95% CI=1.03-4.36). The present study did not show elevated levels of SU in individuals who consumed black tea, coffee, fruit juice or soda.
Alcohol consumption increases SU levels. The finding that daily drinking of green tea is associated with hyperuricaemia needs validation in future studies.
PMCID: PMC3710722  PMID: 23463601
serum urate; coffee; tea; soft drinks; fruit juice; alcohol; Chinese
14.  Serum estrogen receptor bioactivity and breast cancer risk among postmenopausal women 
Endocrine-related cancer  2014;21(2):263-273.
The estrogen levels of Asian women are different from those of Western women, and this could affect estrogen receptor (ER) bioactivity and breast cancer risk. We conducted a case-control study of 169 postmenopausal breast cancer cases and 426 matched controls nested within a population-based prospective cohort, The Singapore Chinese Health Study, to evaluate serum levels of estrogens and their receptor (ERα and ERβ)-mediated estrogenic activities in relation to breast cancer risk. Breast cancer cases had higher levels of estrogens and estrogen receptor mediated bioactivities in baseline serum than controls. Compared to the lowest quartile, women in the highest quartile for estrone or ERα-mediated bioactivity had increased breast cancer risk. After additional adjustment for ERβ bioactivity, free E2 and estrone; serum ERα-mediated estrogenic activity remained associated with increased breast cancer risk. Compared to the lowest quartile, women in the highest quartile for ERα-mediated bioactivity had an odds ratio of 2.39 (95% confidence interval=1.17–4.88, p for trend=0.016). Conversely, the positive association between estrone and cancer risk became null after adjustment for ERα-mediated estrogenic activity, suggesting that the effect of estrone could be mediated through ERα. Identification of the factor(s) contributing to increased ERα-mediated estrogenic bioactivity in sera, and its role as a predictor for breast cancer risk needs to be validated in future studies.
PMCID: PMC3962747  PMID: 24322303
breast cancer; estrogen; estrogen receptor; estrogen receptor bioassay
15.  Fried meat intake is a risk factor for lung adenocarcinoma in a prospective cohort of Chinese men and women in Singapore 
Carcinogenesis  2013;34(8):1794-1799.
Probable human carcinogens are generated during Chinese-style high-temperature cooking of meat and have been detected in the ambient air and on the meat surface. Although the inhalation of these compounds is an established risk factor for lung cancer, exposure via fried meat consumption has not yet been prospectively evaluated as a risk factor. The relationship between fried meat intake and lung cancer risk was investigated using data from a prospective cohort study among Chinese in Singapore. Lung cancer cases (n = 1130) were identified from 61 321 men and women, 70% of whom were lifetime never smokers. Proportional hazards regression methods were used to calculate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs). Overall, there was no association between fried meat intake and risk of all lung cancers combined. For lung adenocarcinoma, fried meat intake had a statistically significant association with increased risk. The association between fried meat intake and risk of lung adenocarcinoma became stronger when analyses were restricted to lifetime never smokers. Compared with the lowest tertile of fried meat intake, the HRs (95% CIs) for the second and third tertiles were 1.43 (0.98, 2.08) and 1.51 (1.03, 2.22), respectively (P for trend = 0.04). The positive association was present among both men and women. There was no association between fried meat intake and risk of non-adenocarcinomas of the lung. Our prospective results for fried meat intake support consumption as an important route of exposure to compounds from Chinese-style high-temperature cooking for the development of lung adenocarcinoma.
PMCID: PMC3731803  PMID: 23568952
16.  Calcium intake is not related to breast cancer risk among Singapore Chinese women 
There is experimental evidence that calcium protects against breast cancer development. Prospective epidemiologic studies supporting a protective effect of calcium on breast cancer risk have mainly been limited to Western populations. We examined the association between calcium intake and breast cancer risk in the Singapore Chinese Health Study, a large population-based prospective cohort. Calcium intake and supplement use was assessed by in-person interviewer using a validated food frequency questionnaire. After a mean follow-up of 14.2±3.5 years, 823 cohort participants developed invasive breast cancer. Multivariate proportional hazards regression models were fitted to examine the associations between calcium intake and breast cancer risk. Vegetables were the primary food source of calcium in this study population, followed by dairy products, grains and soy foods. Calcium intake was not associated with breast cancer risk, comparing highest quartile (>345.6 mg/1000 kcal/day) to lowest quartile (<204.5mg/1000 kcal/day) of intake. There was no evidence of effect modification by menopausal status, body mass index, dietary vitamin D or stage of disease at diagnosis. Our findings do not support a hypothesis for calcium in breast cancer chemoprevention, contrary to findings from previous studies among Western populations with higher calcium intake primarily from dairy products and supplements.
PMCID: PMC3727233  PMID: 23319293
calcium intake; breast cancer; Asian; Chinese; cohort studies
17.  Breast cancer risk assessment using genetic variants and risk factors in a Singapore Chinese population 
Genetic variants for breast cancer risk identified in genome-wide association studies (GWAS) in Western populations require further testing in Asian populations. A risk assessment model incorporating both validated genetic variants and established risk factors may improve its performance in risk prediction of Asian women.
A nested case-control study of female breast cancer (411 cases and 1,212 controls) within the Singapore Chinese Health Study was conducted to investigate the effects of 51 genetic variants identified in previous GWAS on breast cancer risk. The independent effect of these genetic variants was assessed by creating a summed genetic risk score (GRS) after adjustment for body mass index and the Gail model risk factors for breast cancer.
The GRS was an independent predictor of breast cancer risk in Chinese women. The multivariate-adjusted odds ratios (95% confidence intervals) of breast cancer for the second, third, and fourth quartiles of the GRS were 1.26 (0.90 to 1.76), 1.47 (1.06 to 2.04) and 1.75 (1.27 to 2.41) respectively (P for trend <0.001). In addition to established risk factors, the GRS improved the classification of 6.2% of women for their absolute risk of breast cancer in the next five years.
Genetic variants on top of conventional risk factors can improve the risk prediction of breast cancer in Chinese women.
PMCID: PMC4095592  PMID: 24941967
18.  Western-Style Fast Food Intake and Cardiometabolic Risk in an Eastern Country 
Circulation  2012;126(2):182-188.
Western-style fast food contributes to a dietary pattern portending poor cardiometabolic health in the United States. With globalization, this way of eating is becoming more common in developing and recently developed populations.
Methods and Results
We examined the association of Western-style fast food intake with risk of incident type 2 diabetes mellitus and coronary heart disease mortality in Chinese Singaporeans. This analysis included men and women 45 to 74 years of age who enrolled in the Singapore Chinese Health Study from 1993 to 1998. For CHD mortality, 52 584 participants were included and 1397 deaths were identified through December 31, 2009, via registry linkage. For type 2 diabetes mellitus, 43 176 participants were included and 2252 cases were identified during the follow-up interview (1999 –2004) and validated. Hazard ratios for incident type 2 diabetes mellitus and coronary heart disease mortality were estimated with thorough adjustment for demographic, lifestyle, and dietary factors. Chinese Singaporeans with relatively frequent intake of Western-style fast food items (≥2 times per week) had an increased risk of developing type 2 diabetes mellitus (hazard ratio, 1.27; 95% confidence interval, 1.03–1.54) and dying of coronary heart disease (hazard ratio, 1.56; 95% confidence interval, 1.18 –2.06) relative to their peers with little or no reported intake. These associations were not materially altered by adjustments for overall dietary pattern, energy intake, and body mass index.
Western-style fast food intake is associated with increased risk of developing type 2 diabetes mellitus and of coronary heart disease mortality in an Eastern population. These findings suggest the need for further attention to global dietary acculturation in the context of ongoing epidemiological and nutrition transitions.
PMCID: PMC4059207  PMID: 22753304
coronary disease; diabetes mellitus; type 2; epidemiology; food; mortality
19.  Association between Body-Mass Index and Risk of Death in More Than 1 Million Asians 
The New England journal of medicine  2011;364(8):719-729.
Most studies that have evaluated the association between the body-mass index (BMI) and the risks of death from any cause and from specific causes have been conducted in populations of European origin.
We performed pooled analyses to evaluate the association between BMI and the risk of death among more than 1.1 million persons recruited in 19 cohorts in Asia. The analyses included approximately 120,700 deaths that occurred during a mean follow-up period of 9.2 years. Cox regression models were used to adjust for confounding factors.
In the cohorts of East Asians, including Chinese, Japanese, and Koreans, the lowest risk of death was seen among persons with a BMI (the weight in kilograms divided by the square of the height in meters) in the range of 22.6 to 27.5. The risk was elevated among persons with BMI levels either higher or lower than that range — by a factor of up to 1.5 among those with a BMI of more than 35.0 and by a factor of 2.8 among those with a BMI of 15.0 or less. A similar U-shaped association was seen between BMI and the risks of death from cancer, from cardiovascular diseases, and from other causes. In the cohorts comprising Indians and Bangladeshis, the risks of death from any cause and from causes other than cancer or cardiovascular disease were increased among persons with a BMI of 20.0 or less, as compared with those with a BMI of 22.6 to 25.0, whereas there was no excess risk of either death from any cause or cause-specific death associated with a high BMI.
Underweight was associated with a substantially increased risk of death in all Asian populations. The excess risk of death associated with a high BMI, however, was seen among East Asians but not among Indians and Bangladeshis.
PMCID: PMC4008249  PMID: 21345101
20.  Burden of Total and Cause-Specific Mortality Related to Tobacco Smoking among Adults Aged ≥45 Years in Asia: A Pooled Analysis of 21 Cohorts 
PLoS Medicine  2014;11(4):e1001631.
Wei Zheng and colleagues quantify the burden of tobacco-smoking-related deaths for adults in Asia.
Please see later in the article for the Editors' Summary
Tobacco smoking is a major risk factor for many diseases. We sought to quantify the burden of tobacco-smoking-related deaths in Asia, in parts of which men's smoking prevalence is among the world's highest.
Methods and Findings
We performed pooled analyses of data from 1,049,929 participants in 21 cohorts in Asia to quantify the risks of total and cause-specific mortality associated with tobacco smoking using adjusted hazard ratios and their 95% confidence intervals. We then estimated smoking-related deaths among adults aged ≥45 y in 2004 in Bangladesh, India, mainland China, Japan, Republic of Korea, Singapore, and Taiwan—accounting for ∼71% of Asia's total population. An approximately 1.44-fold (95% CI = 1.37–1.51) and 1.48-fold (1.38–1.58) elevated risk of death from any cause was found in male and female ever-smokers, respectively. In 2004, active tobacco smoking accounted for approximately 15.8% (95% CI = 14.3%–17.2%) and 3.3% (2.6%–4.0%) of deaths, respectively, in men and women aged ≥45 y in the seven countries/regions combined, with a total number of estimated deaths of ∼1,575,500 (95% CI = 1,398,000–1,744,700). Among men, approximately 11.4%, 30.5%, and 19.8% of deaths due to cardiovascular diseases, cancer, and respiratory diseases, respectively, were attributable to tobacco smoking. Corresponding proportions for East Asian women were 3.7%, 4.6%, and 1.7%, respectively. The strongest association with tobacco smoking was found for lung cancer: a 3- to 4-fold elevated risk, accounting for 60.5% and 16.7% of lung cancer deaths, respectively, in Asian men and East Asian women aged ≥45 y.
Tobacco smoking is associated with a substantially elevated risk of mortality, accounting for approximately 2 million deaths in adults aged ≥45 y throughout Asia in 2004. It is likely that smoking-related deaths in Asia will continue to rise over the next few decades if no effective smoking control programs are implemented.
Please see later in the article for the Editors' Summary
Editors' Summary
Every year, more than 5 million smokers die from tobacco-related diseases. Tobacco smoking is a major risk factor for cardiovascular disease (conditions that affect the heart and the circulation), respiratory disease (conditions that affect breathing), lung cancer, and several other types of cancer. All told, tobacco smoking kills up to half its users. The ongoing global “epidemic” of tobacco smoking and tobacco-related diseases initially affected people living in the US and other Western countries, where the prevalence of smoking (the proportion of the population that smokes) in men began to rise in the early 1900s, peaking in the 1960s. A similar epidemic occurred in women about 40 years later. Smoking-related deaths began to increase in the second half of the 20th century, and by the 1990s, tobacco smoking accounted for a third of all deaths and about half of cancer deaths among men in the US and other Western countries. More recently, increased awareness of the risks of smoking and the introduction of various tobacco control measures has led to a steady decline in tobacco use and in smoking-related diseases in many developed countries.
Why Was This Study Done?
Unfortunately, less well-developed tobacco control programs, inadequate public awareness of smoking risks, and tobacco company marketing have recently led to sharp increases in the prevalence of smoking in many low- and middle-income countries, particularly in Asia. More than 50% of men in many Asian countries are now smokers, about twice the prevalence in many Western countries, and more women in some Asian countries are smoking than previously. More than half of the world's billion smokers now live in Asia. However, little is known about the burden of tobacco-related mortality (deaths) in this region. In this study, the researchers quantify the risk of total and cause-specific mortality associated with tobacco use among adults aged 45 years or older by undertaking a pooled statistical analysis of data collected from 21 Asian cohorts (groups) about their smoking history and health.
What Did the Researchers Do and Find?
For their study, the researchers used data from more than 1 million participants enrolled in studies undertaken in Bangladesh, India, mainland China, Japan, the Republic of Korea, Singapore, and Taiwan (which together account for 71% of Asia's total population). Smoking prevalences among male and female participants were 65.1% and 7.1%, respectively. Compared with never-smokers, ever-smokers had a higher risk of death from any cause in pooled analyses of all the cohorts (adjusted hazard ratios [HRs] of 1.44 and 1.48 for men and women, respectively; an adjusted HR indicates how often an event occurs in one group compared to another group after adjustment for other characteristics that affect an individual's risk of the event). Compared with never smoking, ever smoking was associated with a higher risk of death due to cardiovascular disease, cancer (particularly lung cancer), and respiratory disease among Asian men and among East Asian women. Moreover, the researchers estimate that, in the countries included in this study, tobacco smoking accounted for 15.8% of all deaths among men and 3.3% of deaths among women in 2004—a total of about 1.5 million deaths, which scales up to 2 million deaths for the population of the whole of Asia. Notably, in 2004, tobacco smoking accounted for 60.5% of lung-cancer deaths among Asian men and 16.7% of lung-cancer deaths among East Asian women.
What Do These Findings Mean?
These findings provide strong evidence that tobacco smoking is associated with a substantially raised risk of death among adults aged 45 years or older throughout Asia. The association between smoking and mortality risk in Asia reported here is weaker than that previously reported for Western countries, possibly because widespread tobacco smoking started several decades later in most Asian countries than in Europe and North America and the deleterious effects of smoking take some years to become evident. The researchers note that certain limitations of their analysis are likely to affect the accuracy of its findings. For example, because no data were available to estimate the impact of secondhand smoke, the estimate of deaths attributable to smoking is likely to be an underestimate. However, the finding that nearly 45% of the global deaths from active tobacco smoking occur in Asia highlights the urgent need to implement comprehensive tobacco control programs in Asia to reduce the burden of tobacco-related disease.
Additional Information
Please access these websites via the online version of this summary at
The World Health Organization provides information about the dangers of tobacco (in several languages) and about the WHO Framework Convention on Tobacco Control, an international instrument for tobacco control that came into force in February 2005 and requires parties to implement a set of core tobacco control provisions including legislation to ban tobacco advertising and to increase tobacco taxes; its 2013 report on the global tobacco epidemic is available
The US Centers for Disease Control and Prevention provides detailed information about all aspects of smoking and tobacco use
The UK National Health Services Choices website provides information about the health risks associated with smoking
MedlinePlus has links to further information about the dangers of smoking (in English and Spanish)
SmokeFree, a website provided by the UK National Health Service, offers advice on quitting smoking and includes personal stories from people who have stopped smoking, from the US National Cancer Institute, offers online tools and resources to help people quit smoking
PMCID: PMC3995657  PMID: 24756146
21.  Combined Lifestyle Factors and Risk of Incident Colorectal Cancer in a Chinese Population 
A body of research links dietary intake, alcohol consumption, smoking, physical activity, body mass index (BMI), and possibly sleep patterns with colorectal cancer risk. However, little research has examined the association of the combination of these lifestyle factors with incidence of colorectal cancer, especially in non-western populations. A protective lifestyle factor index of these 6 aforementioned factors was created and examined in relation to risk of developing colorectal cancer. This study is a prospective observational study of 50,466 Chinese men and women in Singapore aged 45–74 during enrollment in the Singapore Chinese Health Study in 1993–1998 and followed up through 2007. The main outcome measures were standardized rates and hazard ratios of incident colorectal cancer. The protective levels of each lifestyle factor were independently associated with reduced age- and sex-standardized incidence rates of colon cancer. When all the factors were combined into a single protective lifestyle factor index, there was a strong, monotonic decrease in incidence rate of colon cancer with an increasing score. Relative to participants with an index score of 0–3, the hazard ratios (95% confidence intervals) of colon cancer for an index score of 4, 5, 6, 7, 8, 9/10 were 0.58 (0.35–0.95), 0.56 (0.36–0.86), 0.50 (0.33–0.76), 0.43 (0.28–0.66), 0.39 (0.25–0.63), and 0.25 (0.12–0.54) (P for trend <0.0001). The results were consistent by sex. Conversely, there was no association with rectal cancer risk. An increasing protective lifestyle factor index score is associated with a marked decreased risk of developing colon cancer in Chinese men and women.
PMCID: PMC3618573  PMID: 23275007
Lifestyle; sleep; Colorectal Cancer; Asian
22.  Genetic variation in Transforming Growth Factor beta 1 and mammographic density in Singapore Chinese women 
Cancer research  2013;73(6):1876-1882.
Transforming growth factor-beta (TGF-β) plays a critical role in normal mammary development and morphogenesis. Decreased TGF-β signaling has been associated with increased mammographic density. Percent mammographic density (PMD) adjusted for age and body mass index (BMI) is a strong risk factor and predictor of breast cancer risk. PMD is highly heritable, but few genetic determinants have been identified. We investigated the association between genetic variation in TGFB1 and PMD using a cross-sectional study of 2,038 women who were members of the population-based Singapore Chinese Health Study cohort. We assessed PMD using a computer-assisted method. We used linear regression to examine the association between 9 tagging SNPs of TGFB1 and PMD and their interaction with parity, adjusting for age, BMI, and dialect group. We calculated ‘P-values adjusted for correlated tests’ (PACT) to account for multiple testing. The strongest association was observed for rs2241716. Adjusted PMD was higher by 1.5% per minor allele (PACT =0.04). When stratifying by parity, this association was limited to nulliparous women. For nulliparous women, adjusted PMD was higher by 8.6% per minor allele (PACT=0.003; P for interaction with parity=0.002). Three additional TGFB1 tagging SNPs, which were in linkage disequilibrium with rs2241716, were statistically significantly associated with adjusted PMD (PACT<0.05) for nulliparous women. However, none of these three SNPs showed statistically significant association after adjusting for rs2241716. Our data support that TGFB1 genetic variation may be an important genetic determinant of mammographic density measure that predicts breast cancer risk, particularly in nulliparous women.
PMCID: PMC3740538  PMID: 23333936
TGFB1; polymorphism; mammographic density; Chinese
23.  Sleep duration, spot urinary 6-sulfatoxymelatonin levels and risk of breast cancer among Chinese women in Singapore 
We previously reported an inverse association between sleep duration and breast cancer risk in the prospective, population-based Singapore Chinese Health Study (SCHS) cohort (Wu et al., Carcinogenesis 2008;29:1244–8). Sleep duration was significantly positively associated with 6-sulfatoxymelatonin (aMT6s) levels determined in a spot urine, but aMT6s levels in breast cancer cases were lacking (Wu et al., Carcinogenesis 2008;29:1244–8). We updated the sleep duration–breast cancer association with 14 years of follow-up of 34,028 women in the SCHS. In a nested case–control study conducted within the SCHS, randomly timed, prediagnostic urinary aMT6s concentrations were compared between 248 incident breast cancer and 743 individually matched cohort controls. Three female controls were individually matched to each case on age at baseline interview (within 3 years), dialect group, menopausal status, date of baseline interview (within 2 years), date of urine sample collection (within 6 months) and timing of urine collection during the day (within 1 hr). Cox proportional hazards and conditional regression models with appropriate adjustment for confounders were used to examine the sleep– and aMT6s–breast cancer relationships. Breast cancer risk was not significantly associated with sleep duration; adjusted odds ratio (OR) for 9+ vs. ≤6 hr is 0.89 [95% confidence interval (95% CI) 5 0.64–1.22]. Prediagnostic aMT6s levels did not differ between breast cancer cases and matched controls; adjusted OR for highest versus lowest quartiles is 1.00 (95% CI 5 0.64-1.54). We conclude that sleep duration is not significantly associated with breast cancer risk reduction. Melatonin levels derived from randomly timed spot urine are unrelated to breast cancer. Randomly timed, spot urine-derived melatonin levels are noninformative as surrogates of nocturnal melatonin production.
PMCID: PMC3477268  PMID: 22644618
sleep duration; spot urinary melatonin; breast cancer; prospective; Singaporean Chinese
24.  Joint Effects of Known Type 2 Diabetes Susceptibility Loci in Genome-Wide Association Study of Singapore Chinese: The Singapore Chinese Health Study 
PLoS ONE  2014;9(2):e87762.
Genome-wide association studies (GWAS) have identified genetic factors in type 2 diabetes (T2D), mostly among individuals of European ancestry. We tested whether previously identified T2D-associated single nucleotide polymorphisms (SNPs) replicate and whether SNPs in regions near known T2D SNPs were associated with T2D within the Singapore Chinese Health Study.
2338 cases and 2339 T2D controls from the Singapore Chinese Health Study were genotyped for 507,509 SNPs. Imputation extended the genotyped SNPs to 7,514,461 with high estimated certainty (r2>0.8). Replication of known index SNP associations in T2D was attempted. Risk scores were computed as the sum of index risk alleles. SNPs in regions ±100 kb around each index were tested for associations with T2D in conditional fine-mapping analysis.
Of 69 index SNPs, 20 were genotyped directly and genotypes at 35 others were well imputed. Among the 55 SNPs with data, disease associations were replicated (at p<0.05) for 15 SNPs, while 32 more were directionally consistent with previous reports. Risk score was a significant predictor with a 2.03 fold higher risk CI (1.69–2.44) of T2D comparing the highest to lowest quintile of risk allele burden (p = 5.72×10−14). Two improved SNPs around index rs10923931 and 5 new candidate SNPs around indices rs10965250 and rs1111875 passed simple Bonferroni corrections for significance in conditional analysis. Nonetheless, only a small fraction (2.3% on the disease liability scale) of T2D burden in Singapore is explained by these SNPs.
While diabetes risk in Singapore Chinese involves genetic variants, most disease risk remains unexplained. Further genetic work is ongoing in the Singapore Chinese population to identify unique common variants not already seen in earlier studies. However rapid increases in T2D risk have occurred in recent decades in this population, indicating that dynamic environmental influences and possibly gene by environment interactions complicate the genetic architecture of this disease.
PMCID: PMC3919750  PMID: 24520337
25.  Asthma and the risk of type 2 diabetes in the Singapore Chinese Health Study 
Asthma is believed to increase the risk for several proinflammatory diseases, yet epidemiologic studies on asthma in relation to risk of developing type 2 diabetes are sparse and have reported inconsistent results. In the present study, we investigated the hypothesis that asthma is associated with an increased risk of incident type 2 diabetes in Chinese adults.
We used data from the Singapore Chinese Health Study, including Chinese men and women aged 45–74 years, free of cancer, heart disease, stroke, and diabetes at baseline (1993–1998) and followed through 2004 for incident physician-diagnosed diabetes. Cox regression models were used to examine the associations between self-reported history of physician-diagnosed asthma and risk of diabetes.
During an average follow-up of 5.7 years per person, 2,234 of the 42,842 participants included in the current analyses reported diagnoses of type 2 diabetes. After adjustment for potential confounders, not including body mass index (BMI), asthma was associated with a 31% increased risk of incident diabetes (HR = 1.31; 95% CI: 1.00–1.72). The association was attenuated after adjustment for adult BMI (HR = 1.25 95% CI: 0.95–1.64). The asthma-diabetes association appeared stronger for adult- versus child-diagnosed asthma cases, and for participants who were obese compared to non-obese.
In Singaporean Chinese adults we observed a positive association between self-reported, physician-diagnosed asthma and risk of developing type 2 diabetes that was modestly attenuated upon adjustment for BMI.
PMCID: PMC3615124  PMID: 23260853
Asthma; Type 2 diabetes; Obesity

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