Adherence to a Mediterranean diet may help prevent cognitive decline in older age, but studies are limited. We examined the association of adherence to the Mediterranean diet with cognitive function and decline.
We included 6,174 participants, aged 65+ years, from the cognitive sub-study of the Women’s Health Study. Women provided dietary information in 1998 and completed a cognitive battery 5 years later, followed by two assessments at 2-year intervals. The primary outcomes were composite scores of global cognition and verbal memory. The alternate Mediterranean diet adherence 9-point-score was constructed based on intakes of: vegetables, fruits, legumes, whole grains, nuts, fish, red and processed meats, moderate alcohol, and the ratio of monounsaturated-to-saturated fats.
After multivariable adjustment, the alternate Mediterranean diet score was not associated with trajectories of repeated cognitive scores (P-trend across quintiles=0.26 and 0.40 for global cognition and verbal memory, respectively), nor with overall global cognition and verbal memory at older ages, assessed by averaging the three cognitive measures (P-trend=0.63 and 0.44, respectively). Among alternate Mediterranean diet components, higher monounsaturated-to-saturated fats ratio was associated with more favorable cognitive trajectories (P-trend=0.03 and 0.05 for global cognition and verbal memory, respectively). Greater whole grain intake was not associated with cognitive trajectories, but was related to better average global cognition (P-trend=0.02).
In this large study of older women, we observed no association of the Mediterranean diet with cognitive decline. Relations between individual Mediterranean diet components, particularly whole grains, and cognitive function merit further study.
Risk reclassification methods have become popular in the medical literature as a means of comparing risk prediction models. In this issue of the Journal, Pencina et al. (Am J Epidemiol. 2012;176(6):492–494) present further results for continuous measures of model discrimination and describe their characteristics in nested models with normally distributed variables. Measures include the change in the area under the receiver operating characteristic curve, the integrated discrimination improvement, and the continuous net reclassification improvement. Although theoretically interesting, these continuous measures may not be the most appropriate to assess clinical utility. The continuous net reclassification improvement, in particular, is a measure of effect rather than model improvement and can sometimes exhibit erratic behavior, as illustrated in 2 examples. Caution is needed before using this as a measure of improvement. Further, the test of the continuous net reclassification improvement and that for the integrated discrimination improvement are similar to the likelihood ratio test in nested models and may be overinterpreted. Reclassification in risk strata, while requiring thresholds, may be more relevant clinically with its ability to examine potential changes in treatment decisions.
calibration; discrimination; model fit; risk prediction
To compare the long-term effectiveness and cost-effectiveness of 3 approaches to managing elevated blood pressure (BP) in adolescents in the United States: no intervention, “screen-and-treat,” and population-wide strategies to lower the entire BP distribution.
We used a simulation model to combine several data sources to project the lifetime costs and cardiovascular outcomes for a cohort of 15-year-old U.S. adolescents under different BP approaches and conducted cost-effectiveness analysis. We obtained BP distributions from the National Health and Nutrition Examination Survey 1999–2004 and used childhood-to-adult longitudinal correlation analyses to simulate the tracking of BP. We then used the coronary heart disease policy model to estimate lifetime coronary heart disease events, costs, and quality-adjusted life years (QALY).
Among screen-and-treat strategies, finding and treating the adolescents at highest risk (eg, left ventricular hypertrophy) was most cost-effective ($18 000/QALY [boys] and $47 000/QALY [girls]). However, all screen-and-treat strategies were dominated by population-wide strategies such as salt reduction (cost-saving [boys] and $650/ QALY [girls]) and increasing physical education ($11 000/QALY [boys] and $35 000/QALY [girls]).
Routine adolescents BP screening is moderately effective, but population-based BP interventions with broader reach could potentially be less costly and more effective for early cardiovascular disease prevention and should be implemented in parallel.
Both physical activity and physical fitness are associated with decreased coronary heart disease (CHD) risk. Our objective was to determine whether genes associated with physical fitness modify the association between physical activity and CHD.
We conducted a prospective cohort study among 23,016 initially healthy women in the Women’s Genome Health Study. Leisure-time physical activity was reported at entry and during follow-up. 58 single nucleotide polymorphisms associated with physical fitness were identified from published literature and summed to create four separate genetic scores related to phenotypes of endurance, muscle strength, VO2max, and overall fitness.
During a median of 14.4 years, 320 incident CHD events occurred. Increased physical activity was associated with lower CHD risk in multivariable-adjusted models (P = 0.0008). Independent of physical activity, only muscle strength genetic score was inversely associated with CHD risk (P = 0.05). There was no evidence that the inverse relation between physical activity and CHD was modified by any of the genetic scores for physical fitness. For overall fitness genetic score, the hazard ratio (HR) per 500 kcal/week of physical activity was 0.85 (95% CI: 0.72, 1.00) in the highest quartile of genetic score; 0.79 (95% CI: 0.67, 0.92) in the lowest quartile (P, interaction = 0.50). For VO2max genetic score, the HR was 0.86 (95% CI 0.72, 1.02) and 0.84 (95% CI 0.72, 0.98), respectively (P, interaction = 0.59).
In this large prospective cohort of women, genes associated with physical fitness did not modify the inverse association between physical activity and CHD risk.
exercise; epidemiology; genetics; cardiovascular disease
Comparing prediction models using reclassification within subgroups at intermediate risk is often of clinical interest.
To demonstrate a method for obtaining an unbiased estimate for the Net Reclassification Improvement (NRI) evaluated only on a subset, or the clinical NRI. Study Design and Setting: We derived the expected value of the clinical NRI under the null hypothesis using the same principles as the overall NRI. We then conducted a simulation study based on a logistic model with a known predictor and a potential predictor, varying the effects of the known and potential predictors to test the performance of our bias-corrected clinical NRI measure. Finally, data from the Women’s Health Study, a prospective cohort of 24,171 female health professionals, were used as an example of the proposed method.
Our bias-corrected estimate is shown to have a mean of zero in the null case under a range of simulated parameters and, unlike the naïve estimate, to be unbiased. We also provide two methods for obtaining a variance estimate, both with reasonable type 1 errors.
Our proposed method is an improvement over currently used methods of calculating the clinical NRI and is recommended to reduce overly optimistic results.
AHA Scientific Statements; communication; decision making; heart failure; heart-assist device; palliative care; prognosis; transplantation
Historically, bipolar disorder and schizophrenia have been considered distinct disorders with different etiologies. Growing evidence suggests that overlapping genetic influences contribute to risk for these disorders and that each disease is genetically heterogeneous. Using cluster analytic methods, we empirically identified homogeneous subgroups of patients, their relatives, and controls based on distinct neurophysiologic profiles. Seven phenotypes were collected from two independent cohorts at two institutions. K-means clustering was used to identify neurophysiologic profiles. In the analysis of all participants, three distinct profiles emerged: “globally impaired”, “sensory processing”, and “high cognitive”. In a secondary analysis, restricted to patients only, we observed a similar clustering into three profiles. The neurophysiological profiles of the SZ and BPD patients did not support the DSM diagnostic distinction between these two disorders. Smokers in the globally impaired group smoked significantly more cigarettes than those in the sensory processing or high cognitive groups. Our results suggest that empirical analyses of neurophysiological phenotypes can identify potentially biologically relevant homogenous subgroups independent of diagnostic boundaries. We hypothesize that each neurophysiology subgroup may share similar genotypic profiles, which may increase statistical power to detect genetic risk factors.
bipolar disorder; schizophrenia; K-means clustering; neurophysiologic profiles
Despite widespread use of multivitamin supplements, their effect on cognitive health – a critical issue with aging – remains inconclusive. To date, there have been no long-term clinical trials to study multivitamin use and cognitive decline in older persons.
To evaluate whether long-term multivitamin supplementation affects cognitive health in later-life.
Randomized, double-blind, placebo-controlled trial of a multivitamin from 1997 to June 1, 2011. The cognitive function sub-study began in 1998; we completed up to four repeated cognitive assessments by telephone interview over 12 years.
The Physicians’ Health Study II.
5,947 male physicians aged ≥ 65 years.
Daily multivitamin, or placebo.
A global composite score averaging 5 tests of global cognition, verbal memory, and category fluency. The secondary endpoint was a verbal memory score combining 4 tests of verbal memory, a strong predictor of Alzheimer disease.
There was no difference in the mean cognitive change over time between the multivitamin and placebo groups, or in the mean level of cognition at any of the four assessments. Specifically, for the global composite score, the mean difference in cognitive change over follow-up was −0.01 (95% confidence interval [CI] −0.04, 0.02) standard units, comparing treatment versus placebo. Similarly, there was no difference in cognitive performance between the treated and placebo groups on the secondary outcome, verbal memory (e.g., mean difference in cognitive change over follow-up=−0.005, 95% CI −0.04, 0.03).
Doses of vitamins may be too low, or population may be too well-nourished to benefit from multivitamin.
In male physicians aged ≥ 65 years, long-term use of a daily multivitamin did not provide cognitive benefits.
http://www.clinicaltrials.gov identifier: NCT00270647
multivitamin; cognitive function; randomized clinical trial; men
Folic acid, vitamin B6, and vitamin B12 act in concert in the one-carbon metabolism and may protect against colorectal neoplasia. We examined the effect of combined B-vitamin treatment on the occurrence of colorectal adenoma.
The Women’s Antioxidant and Folic Acid Cardiovascular Study was a randomized, double-blind, placebo-controlled trial of 5442 female health professionals at high risk for cardiovascular disease from April 1998 through July 2005. Participants were randomly assigned to receive a combination pill of folic acid (2.5mg), vitamin B6 (50mg), and vitamin B12 (1mg) or placebo. This study included 1470 participants who were followed up for as long as 9.2 years and underwent an endoscopy at any point during follow-up. We estimated relative risks using a generalized linear model with a natural logarithm link function and Poisson distributed errors. All statistical tests were two-sided.
The risk of colorectal adenoma was similar among participants receiving treatment (24.3%, 180 of 741 participants) vs placebo (24.0%, 175 of 729 participants) (multivariable adjusted relative risk = 1.00, 95% confidence interval = 0.83 to 1.20). Treatment was not associated with the risk of adenoma when data were analyzed by subsite, size, stage, and the number of adenomas. There was no statistically significant effect modification by alcohol intake, history of cancer or adenoma, or baseline plasma levels or intakes of folate, vitamin B6, or vitamin B12.
Our results indicate no statistically significant effect of combined folic acid, vitamin B6, and vitamin B12 treatment on colorectal adenoma among women at high risk for cardiovascular disease.
Although studies have shown health benefits for moderate-intensity physical activity, there is limited evidence to support beneficial effects for high amounts of vigorous activity among middle-aged and older men. The objective of this study was to examine the relationship between vigorous-intensity physical activity, compared to moderate-intensity activity, and risk of major chronic disease in men.
We prospectively examined the associations between vigorous- and moderate-intensity physical activity and risk of major chronic disease among 44,551 men aged 40–75 years in 1986. Leisure-time physical activity was assessed biennially by questionnaire. During 22 years of follow-up, we documented 14,162 incident cases of major chronic disease, including 4769 cardiovascular events, 6449 cancer events, and 2944 deaths from other causes.
The hazard ratio (HR) of major chronic disease comparing ≥ 21 to 0 MET-hours/week of exercise was 0.86 (95% CI: 0.81, 0.91) for vigorous-intensity activity and 0.85 (95% CI: 0.80, 0.90) for moderate activity. For CVD, the corresponding HR were 0.78 (95% CI: 0.70, 0.86) and 0.80 (95% CI: 0.72, 0.88), respectively. When examined separately, running, tennis, and brisk walking were inversely associated with CVD risk. Furthermore, more vigorous activity was associated with lower disease risk; the HR comparing >70 to 0 MET-hours/week of vigorous-intensity exercise was 0.79 (95% CI: 0.68, 0.92; P <0.0001 for trend) for major chronic disease and 0.73 (95% CI: 0.56, 0.96; P <0.0001 for trend) for CVD.
Vigorous- and moderate-intensity physical activity were associated with lower risk of major chronic disease and cardiovascular disease. Increasing amounts of vigorous activity remained inversely associated with disease risk, even among men in the highest categories of exercise.
exercise; epidemiology; cardiovascular disease; cancer; risk factors
Adiponectin may have a protective role in the development of obesity-related metabolic and vascular disorders including hypertension. We conducted a prospective, nested case-control study to investigate the relationship between baseline plasma adiponectin, measures of adiposity, and subsequent risk of hypertension.
We selected 400 White and 400 Black postmenopausal women, aged <70 years, who have developed incident hypertension during 5.9-year follow-up and an equal number of age and race matched controls in the Women's Health Initiative Observational Study. We measured plasma concentrations of total adiponectin in their baseline bloods.
In crude matched models, plasma adiponectin was inversely associated with risk of hypertension among both White and Black women. The association appeared to be non-linear in White women but dose-related in Black women. Adjustment for lifestyle factors, measures of obesity, and obesity-related clinical factors attenuated these associations. The multivariable relative risks (95% confidence interval) of hypertension across increasing quartiles of plasma adiponectin were 1.00, 0.98 (0.66-1.46), 0.63 (0.41-0.97), and 0.92 (0.60-1.42) in White women (p, trend: 0.38) and 1.00, 0.96 (0.64-1.46), 0.83 (0.53-1.29), and 0.58 (0.36-0.94) in Black women (p, trend: 0.02). Further adjustment for inflammatory markers and endothelial markers eliminated the association in White, but not Black, women.
In this prospective, nested case-control study, we found an inverse association between plasma adiponectin and risk of hypertension in White and Black postmenopausal women. The reduced risk of hypertension was limited to intermediate levels of adiponectin in White women while was graded across quartiles of adiponectin in Black women.
adiponectin; hypertension; epidemiology; prospective study; postmenopausal women
Many novel and emerging risk factors exhibit a significant association with cardiovascular disease, but have not been found to improve risk prediction. Statistical criteria used to evaluate such models and markers have largely relied on the receiver operating characteristic curve, which is an insensitive measure of improvement. Recently, new methods have been developed based on risk reclassification, or changes in risk strata following use of a new marker or model. Associated measures based on both calibration and discrimination have been proposed. This review describes previous methods used to evaluate models as well as the newly developed methods to evaluate clinical utility.
Screening mammography can distort estimated effects in breast cancer risk models due to associations with other risk factors. Mammography information was available in the Nurses’ Health Study from 1988, and 1,815 incident breast cancers were accrued through 2000 among 55,625 women with risk factor data. Logistic models were fit for screening mammography, and inverse probability weighting was used to adjust parameters in an established breast cancer risk model. Approximately 80% of women in each 2-year follow-up period had screening mammograms, which were positively associated with history of benign breast disease, family history of breast cancer, hormone therapy, alcohol use, physical activity, multivitamins, and calcium supplements, and negatively associated with postmenopause, current smoking, and body mass index. Markers of medical attention, including hypertension, high cholesterol, and osteoarthritis, were positively associated, while cardiovascular disease was negative. Inverse probability weighting led to small changes in effects of benign breast disease, family history, and hormone therapy. An apparent reduced risk associated with current smoking in unadjusted models was eliminated after weighting. Thus, several risk factors for breast cancer and cancer diagnosis are associated with mammographic screening. Adjustment for screening had some impact on breast cancer prediction in this cohort, especially for hormone therapy and smoking.
breast neoplasms; hormone replacement therapy; mammography; mass screening; probability weighting; risk factors
Sex steroid hormones have been postulated to involve in blood pressure (BP) regulation. We examine the association of endogenous sex hormone levels with longitudinal change of BP and risk of developing hypertension in initially normotensive postmenopausal women.
We conducted prospective analysis among 619 postmenopausal women free of hypertension at baseline in the Multi-Ethnic Study of Atherosclerosis (MESA). Change of BP and development of incident hypertension were assessed during a mean of 4.8 years follow-up.
After adjusting for age, race/ethnicity, and lifestyle factors, baseline serum estradiol (E2), total and bioavailable testosterone (T), dehydroepiandrosterone (DHEA) were each positively and sex- hormone binding globulin (SHBG) was inversely associated with risk of hypertension. Additional adjustment for body mass index eliminated the associations for E2 and T but only attenuated the associations for DHEA and SHBG. The corresponding multivariable hazard ratios (95% CIs) in the highest quartile were 1.28 (0.83–1.97) for E2, 1.38 (0.89–2.14) for total T, 1.42 (0.90–2.23) for bioavailable T, 1.54 (1.02–2.31) for DHEA, and 0.48 (0.30–0.76) for SHBG. Adjustment for fasting glucose, insulin, and C-reactive protein further attenuated the association for DHEA but not SHBG. Associations of sex hormones with longitudinal BP change were similar.
In postmenopausal women, higher endogenous E2, T, and DHEA and lower SHBG were associated with higher incidence of hypertension and greater longitudinal rise in BP. The associations for E2, T, and DHEA were mostly explained by adiposity, while the association for SHBG was independent of measures of adiposity, insulin resistance, and systemic inflammation.
sex steroid hormones; hypertension; blood pressure; postmenopausal women; prospective study; epidemiology
Findings regarding the association of lipoprotein-associated phospholipase A2 (Lp-PLA2) activity and mass with incident cardiovascular disease (CVD) have been inconsistent, and their role in risk prediction is uncertain.
A case-cohort sample from the Women’s Health Initiative Observational Study (WHI-OS) comprised 1,821 CVD cases and a subcohort of 1,992. Cox regression models with inverse sampling weights assessed the association of Lp-PLA2 mass and activity with CVD (myocardial infarction [MI], stroke, and CVD mortality).
Subcohort means were 184.3 mmol/min/mL for Lp-PLA2 activity and 499.2 ng/mL for Lp-PLA2 mass, with 99% having mass above 200 ng/mL, the clinically recommended cut-point. Both activity and mass were positively associated with incident CVD in age- and race/ethnicity-adjusted analyses. Following adjustment by CVD risk factors, the association with activity became null (hazard ratio [HR] = 1.02 for top vs. bottom quartile, 95% confidence interval [CI] = 0.79-1.33, p-trend=0.65), but the association with mass remained (HR = 1.84, 95% CI = 1.45-2.34, p-trend <0.0001). In contrast to blood pressure, HDL, and hsCRP, reclassification statistics for Lp-PLA2 mass did not suggest improvement for overall CVD after full adjustment.
In the WHI-OS Lp-PLA2 mass, but not activity, was independently associated with CVD. However, model fit did not significantly improve with Lp-PLA2, and assay calibration remains a clinical concern.
Models for risk prediction are widely used in clinical practice to risk stratify and assign treatment strategies. The contribution of new biomarkers has largely been based on the area under the receiver operating characteristic curve, but this measure can be insensitive to important changes in absolute risk. Methods based on risk stratification have recently been proposed to compare predictive models. These include the reclassification calibration statistic, the net reclassification improvement (NRI), and the integrated discrimination improvement (IDI). This work demonstrates the use of reclassification measures, and illustrates their performance for well-known cardiovascular risk predictors in a cohort of women. These measures are targeted at evaluating the potential of new models and markers to change risk strata and alter treatment decisions.
To relate dietary fat types to cognitive change in healthy community-based elders.
Among 6,183 older participants in the Women’s Health Study, we related intake of major fatty acids (FAs) (saturated [SFA], mono-unsaturated [MUFA], total poly-unsaturated [PUFA], trans-unsaturated) to late-life cognitive trajectory. Serial cognitive testing, conducted over 4 years, began 5 years post-dietary assessment. Primary outcomes were global cognition (averaging tests of general cognition, verbal memory and semantic fluency) and verbal memory (averaging tests of recall). We used analyses of response profiles and logistic regression to estimate multivariable-adjusted differences in cognitive trajectory and risk of worst cognitive change (worst 10%) by fat intake.
Higher SFA intake was associated with worse global cognitive (p-linear-trend=0.008) and verbal memory (p-linear-trend=0.01) trajectories. There was a higher risk of worst cognitive change, comparing highest vs. lowest SFA quintiles: the multivariable-adjusted odds ratio (OR) (95% confidence interval, CI) was 1.64 (1.04,2.58) for global cognition and 1.65 (1.04,2.61) for verbal memory. By contrast, higher MUFA intake was related to better global cognitive (p-linear-trend<0.001) and verbal memory (p-linear-trend=0.009) trajectories, and lower OR (95% CI) of worst cognitive change in global cognition (0.52 [0.31,0.88]) and verbal memory (0.56 [0.34,0.94]). Total fat, PUFA, and trans fat intakes were not associated with cognitive trajectory.
Higher SFA intake was associated with worse global cognitive and verbal memory trajectories, while higher MUFA intake was related to better trajectories. Thus, different consumption levels of the major specific fat types, rather than total fat intake itself, appeared to influence cognitive aging.
Randomized evidence for aspirin in the primary prevention of cardiovascular disease (CVD) among women is limited and suggests at most a modest effect for total CVD. Lack of compliance, however, can null-bias estimated effects. We used marginal structural models (MSMs) to estimate the etiologic effect of continuous aspirin use on CVD events among 39,876 apparently healthy female health professionals aged 45 years and older in the Women’s Health Study, a randomized trial of 100 mg aspirin every other day versus placebo. As-treated analyses and MSMs controlled for time-varying determinants of aspirin use and CVD. Predictors of aspirin use differed by randomized group and prior use and included medical history, CVD risk factors, and intermediate CVD events. Previously reported intent-to-treat analyses found small non-significant effects of aspirin on total CVD (hazard ratio (HR) =0.91, 95% confidence interval (CI) =0.81–1.03) and CVD mortality (HR=0.95, 95% CI=0.74–1.22). As-treated analyses were similar for total CVD with a slight reduction in CVD mortality (HR=0.88, 95%CI=0.67–1.16). MSMs, which adjusted for non-compliance, were similar for total CVD (HR=0.93; 95% CI: 0.81, 1.07) but suggested lower CVD mortality with aspirin use (HR = 0.76; 95% CI: 0.54, 1.08). Adjusting for non-compliance had little impact on the estimated effect of aspirin on total CVD, but strengthened the effect on CVD mortality. These results support a limited effect of low-dose aspirin on total CVD in women, but potential benefit for CVD mortality.
Aspirin; cardiovascular disease; marginal structural model; myocardial infarction; stroke
Framingham-based and Reynolds risk scores for cardiovascular disease (CVD) prediction have not been directly compared in an independent validation cohort.
Methods and Results
We selected a case-cohort sample of the multi-ethnic Women’s Health Initiative Observational Cohort, comprising 1722 cases of major CVD (752 MIs, 754 ischemic strokes, and 216 other CVD deaths) and a random subcohort of 1994 women without prior CVD. We estimated risk using the ATP-III score, the Reynolds risk score, and the Framingham CVD model, reweighting to reflect cohort frequencies. Predicted 10-year risk varied widely between models, with 10% or higher risk in 6%, 10%, and 41% of women using the ATP-III, Reynolds, and Framingham CVD models, respectively. Calibration was adequate for the Reynolds model, but the ATP-III and Framingham CVD models over-estimated risk for CHD and major CVD, respectively. After recalibration, the Reynolds model demonstrated improved discrimination over the ATP-III model through a higher c-statistic (0.765 vs. 0.757, p=0.03), positive net reclassification improvement (NRI) (4.9%, p=0.02) and positive integrated discrimination improvement (IDI) (4.1%, p<0.0001) overall, excluding diabetics (NRI=4.2%, p=0.01), and in white (NRI=4.3%, p=0.04) and black (NRI=11.4, p=0.13) women. The Reynolds (NRI=12.9, p<0.0001) and ATP-III (NRI=5.9%, p=0.0001) models demonstrated better discrimination than the Framingham CVD model.
The Reynolds Risk Score was better calibrated than the Framingham-based models in this large external validation cohort. The Reynolds score also showed improved discrimination overall and in black and white women. Large differences in risk estimates exist between models, with clinical implications for statin therapy.
cardiovascular disease risk factors; models; prediction; risk score; statins
Atrial fibrillation (AF) is associated with adverse outcome. Whether recently discovered genetic risk markers improve AF risk prediction is unknown.
Methods and results
We derived and validated a novel AF risk prediction model from 32 possible predictors in the Women's Health Study (WHS), a cohort of 20 822 women without cardiovascular disease (CVD) at baseline followed prospectively for incident AF (median: 14.5 years). We then created a genetic risk score (GRS) comprised of 12 risk alleles in nine loci and assessed model performance in the validation cohort with and without the GRS. The newly derived WHS AF risk algorithm included terms for age, weight, height, systolic blood pressure, alcohol use, and smoking (current and past). In the validation cohort, this model was well calibrated with good discrimination [C-index (95% CI) = 0.718 (0.684–0.753)] and improved all reclassification indices when compared with age alone. The addition of the genetic score to the WHS AF risk algorithm model improved the C-index [0.741 (0.709–0.774); P = 0.001], the category-less net reclassification [0.490 (0.301–0.670); P < 0.0001], and the integrated discrimination improvement [0.00526 (0.0033–0.0076); P < 0.0001]. However, there was no improvement in net reclassification into 10-year risk categories of <1, 1–5, and 5+% [0.041 (−0.044–0.12); P = 0.33].
Among women without CVD, a simple risk prediction model utilizing readily available risk markers identified women at higher risk for AF. The addition of genetic information resulted in modest improvements in predictive accuracy that did not translate into improved reclassification into discrete AF risk categories.
Women; Atrial fibrillation; Genetics; Risk prediction; Epidemiology
The performance of prediction models can be assessed using a variety of different methods and metrics. Traditional measures for binary and survival outcomes include the Brier score to indicate overall model performance, the concordance (or c) statistic for discriminative ability (or area under the receiver operating characteristic (ROC) curve), and goodness-of-fit statistics for calibration.
Several new measures have recently been proposed that can be seen as refinements of discrimination measures, including variants of the c statistic for survival, reclassification tables, net reclassification improvement (NRI), and integrated discrimination improvement (IDI). Moreover, decision–analytic measures have been proposed, including decision curves to plot the net benefit achieved by making decisions based on model predictions.
We aimed to define the role of these relatively novel approaches in the evaluation of the performance of prediction models. For illustration we present a case study of predicting the presence of residual tumor versus benign tissue in patients with testicular cancer (n=544 for model development, n=273 for external validation).
We suggest that reporting discrimination and calibration will always be important for a prediction model. Decision-analytic measures should be reported if the predictive model is to be used for making clinical decisions. Other measures of performance may be warranted in specific applications, such as reclassification metrics to gain insight into the value of adding a novel predictor to an established model.
Few prospective studies have explored the association between renal function and risk of incident atrial fibrillation (AF) in apparently healthy populations. A total of 24,746 women participating in the Women’s Health Study who were free of cardiovascular disease (CVD), AF and provided a blood sample at baseline were prospectively followed for incident AF from 1993 to 2010. AF events were confirmed by medical chart review. Estimated glomerular filtration rate (eGFR) was calculated from baseline creatinine using the Chronic Kidney Disease – Epidemiology equation. Cox models were used to estimate hazard ratios (HR) and 95% CI for incident AF across eGFR categories controlling for AF risk factors. During 15.4 years (median) of follow-up, 786 incident AF events occurred. The multivariable-adjusted HR for incident AF across eGFR categories (<60, 60–74.9, 75–89, and ≥ 90 ml/min/1.73 m2) were:1.36 (1.00–1.84), 0.90 (0.71–1.14), 0.99 (0.84–1.18) and 1.00, respectively, without evidence of a linear association (P for trend, 0.48). Similarly, there was no significant curvilinear association (P quadratic, 0.10) in multivariable analysis across categories. As compared to women with an eGFR ≥ 60 ml/min/1.73 m2, the 1008 women with an eGFR < 60 ml/min/1.73 m2 had a multivariable adjusted HR for AF of 1.39 (1.04–1.86, p value 0.03). In conclusion, no significant linear or curvilinear relationship was observed between incident AF and less severe impairment of renal function in this large prospective cohort of women. However, a significant elevation in AF risk was observed at a threshold eGFR of < 60 ml/min/1.73 m2.
atrial fibrillation; renal function
Data from laboratory studies, observational research, and/or secondary prevention trials suggest that vitamin D and marine omega-3 fatty acids may reduce risk for cancer or cardiovascular disease (CVD), but primary prevention trials with adequate dosing in general populations (i.e., unselected for disease risk) are lacking. The ongoing VITamin D and OmegA-3 TriaL (VITAL) is a large randomized, double-blind, placebo-controlled, 2×2 factorial trial of vitamin D (in the form of vitamin D3 [cholecalciferol], 2000 IU/day) and marine omega-3 fatty acid (Omacor® fish oil, eicosapentaenoic acid [EPA] + docosahexaenoic acid [DHA], 1 g/day) supplements in the primary prevention of cancer and CVD among a multi-ethnic population of 20,000 U.S. men aged ≥50 and women aged ≥55. The mean treatment period will be 5 years. Baseline blood samples will be collected in at least 16,000 participants, with follow-up blood collection in about 6000 participants. Yearly follow-up questionnaires will assess treatment compliance (plasma biomarker measures will also assess compliance in a random sample of participants), use of non-study drugs or supplements, occurence of endpoints, and cancer and vascular risk factors. Self-reported endpoints will be confirmed by medical record review by physicians blinded to treatment assignment, and deaths will be ascertained through national registries and other sources. Ancillary studies will investigate whether these agents affect risk for diabetes and glucose intolerance; hypertension; cognitive decline; depression; osteoporosis and fracture; physical disability and falls; asthma and other respiratory diseases; infections; rheumatoid arthritis, systemic lupus erythematosus, thyroid diseases, and other autoimmune disorders.
Cancer; cardiovascular disease; cholecalciferol; primary prevention; omega-3 fatty acids; vitamin D; randomized controlled trial
To identify women who benefit from aspirin 100 mg on alternate days for primary prevention of vascular events by using treatment effect prediction based on individual patient characteristics.
Methods and results
Randomized controlled trial data from the Women's Health Study were used to predict treatment effects for individual women in terms of absolute risk reduction for major cardiovascular events (i.e. myocardial infarction, stroke, or cardiovascular death). Predictions were based on existing risk scores, i.e. Framingham (FRS), and Reynolds (RRS), and on a newly developed prediction model. The net benefit of different aspirin treatment-strategies was compared: (i) treat no one, (ii) treat everyone, (iii) treatment according to the current guidelines (i.e. selective treatment of women >65 years of age or having >10% FRS), and (iv) prediction-based treatment (i.e. selective treatment of patients whose predicted treatment effect exceeds a given decision threshold). The predicted reduction in 10-year absolute risk for major cardiovascular events was <1% in 97.8% of 27 939 study subjects when based on the refitted FRS, in 97.0% when based on the refitted RRS, and in 90.0% when based on the newly developed model. Of the treatment strategies considered, only prediction-based treatment using the newly developed model and selective treatment of women >65 years of age yielded more net benefit than treating no one, provided that the 10-year number-willing-to-treat (NWT) to prevent one cardiovascular event was above 50.
Aspirin was ineffective or even harmful in the majority of patients. Age was positively related to treatment effect, whereas current smoking and baseline risk for cardiovascular events were not. When the NWT is 50 or lower, the aspirin treatment strategy that is associated with optimal net benefit in primary prevention of vascular events in women is to treat none.
Trial registration information: Clinicaltrials.gov identifier number: NCT00000479.
Aspirin; Primary prevention; Treatment effect prediction; Net benefit