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To investigate whether a high consumption of red or processed meat is associated with increased risk of coronary heart disease.
The subjects were 517 men and 635 women who were members of the Medical Research Council National Survey of Health and Development, 1946 birth cohort. Assessment of diet was carried out at two time-points 1989 and 1999 with outcome measures collected in 1999. Food intake data were recorded in 5 -day diaries. Meat consumption was estimated by adding individual meat portions to the meat fractions of composite dishes.
There was no significant association between red or processed meat consumption in 1989 and 1999 and serum cholesterol concentrations and blood pressure measured in 1999. The combined intake of red and processed meat in 1999 had a significant positive association with blood pressure in men only. Red and processed meat intakes in 1989 separately and combined had a significant positive association with waist circumference in 1999: a 10g increase in red meat consumption accounted for a 0.3cm increase in waist circumference; p=0.04 (men), 0.05 (women).
Consumption of red or processed meat assessed separately was not related to the major risk factors for CHD but did contribute to increased waist circumference that has also been identified as a risk factor.
While there has been a steady decline since 1980, death rates from coronary heart disease (CHD) in the United Kingdom (UK) are still among the highest in Western Europe. The latest data available for the UK reported 105,842 deaths, men and women combined, in 2004 (British Heart Foundation 2007). At least 75% of new cases of CHD can be explained by inappropriate diet, low level of physical activity and smoking, as primarily expressed through unfavorable serum lipid concentrations, high body mass index (BMI) and raised blood pressure (Beaglehole and Magnus 2002). Numerous studies have demonstrated that an increase in saturated fat intake is associated with elevated blood total cholesterol levels (Clarke et al. 1997; Tang et al. 1998; Safeer and Ugalat 2002; German and Dillard 2004; Li et al. 2005), while a high intake of sodium is associated with hypertension (Law et al. 1991; Appel et al. 1997; Krauss et al. 2000).
Meat and meat products are important sources of saturated fat and sodium in the UK contributing 23% and 26% to the mean intake overall respectively (Henderson et al. 2003). Red meat consumption is a characteristic of the typical northern European diet, which also contains large quantities of dairy products, highly refined carbohydrates, hydrogenated fats, and small quantities of vegetables and fruit (Kushi et al. 1995). This dietary pattern has been shown to be related to an increased risk of CHD (Kushi et al. 1995; Appel et al. 1997; Hu et al. 1999; Hu et al. 2000; Miura et al. 2004;). However, meat is an important source of high quality protein and micronutrients: B-vitamins, zinc, haem-iron and vitamins A and D (Linseisen et al. 2002; Cosgrove et al. 2005).
Meat is a diverse food group and the quantity of macro- and micronutrients varies for different types of meat. For example, fat content can range between 4% (lean poultry) and 40% (fatty red meat) (Linseisen et al. 2002). Furthermore, meat is often a part of mixed dishes containing vegetables and/or cereals so it is important to disaggregate meat from composite foods to prevent incorrect estimates of meat consumption (Cosgrove et al. 2005).
It has been reported that the consumption of both red and processed meat are associated with risk factors for CHD; in particular, raised total cholesterol and low- density-lipoprotein (LDL) cholesterol concentrations, greater body mass index (BMI) and raised blood pressure (Slattery et al. 1991; Miura et al. 2004; Steffen et al. 2005). The aim of this study is to examine the relationship between consumption of red and processed meat, after disaggregation of composite dishes, with risk factors for CHD using the data from the UK Medical Research Council (MRC) National Survey of Health and Development (NSHD) 1946 Birth Cohort. This is a longitudinal survey, in which dietary and health data have been collected at several time points during adult life. Meat consumption was assessed in 1989 and 1999 and related to risk factors assessed in 1999. Thus it was possible to investigate whether meat consumption could predict CHD risk ten years later.
The study population comprised 1152 men and women who were members of the MRC National Survey of Health and Development (NSHD). This cohort is a social-class-stratified random sample of 5362 singleton legitimate births in England, Scotland and Wales during the first week of March 1946. When survey members were aged 43 and 53, in 1989 and 1999 respectively, a research nurse visited and interviewed them in their own homes. Subjects were asked to record their diet in 5-day diaries. Blood pressure and anthropometric data were measured and, in 1999 only, non-fasting venous blood samples were drawn. The present analyses were of data collected from subjects who completed at least three days of the food diary in 1989 and 1999 and for whom serum cholesterol levels, blood pressure, BMI, and waist circumference were measured in 1999. Members of the cohort who were visited in 1989 and 1999 were representative of the native born population of a similar age (Wadsworth et al. 1992; Wadsworth et al. 2003). However, due to the selection requirements for this study, the number of subjects was less than all those contacted in 1999 and there was a bias towards non-manual socio-economic classes.
All food and drink consumed was recorded using household measures with portion sizes estimated according to detailed guidance notes and photographs provided in the diary. The diaries were coded using the in-house program DIDO (Diet In Data Out). Weights of meat, meat dishes, and meat products were calculated from the coded food diary using the in-house suite of programs based on McCance and Widdowson’s The Composition of Foods, fourth and sixth edition (Paul A.A. 1978; Food Standards Agency 2002). In total, 140 food codes that contained meat were recorded in 1989 and 210 in 1999. Of these, 44% in 1989 and 56% in 1999 were composite dishes containing a variable percentage of meat. The meat content of each of these mixed dishes was calculated and added to individual meat portions to arrive at a more precise measure of total meat intake (Prynne et al. 2007).
The analyses were based on the consumption of the two meat categories:
Since the intake of offal and game was very low, they were omitted from all the analysis.
Information about lifestyle, demographic factors and socio-economic status was collected at home visits by research nurses trained by study staff in 1989 and 1999.
Socio-economic status and region were defined at age 43. Socio-economic status was based on occupation and categorized into non-manual (managerial, professional, skilled professional ancillaries and service providers) and manual (skilled, non-skilled and agricultural workers). Three regions of residence were defined: 1) Scotland, North, North West and Yorkshire 2) Midlands, North Midlands, Eastern and Wales 3) South West, Southern, London and South East. Alcohol consumption was calculated from the dietary records in grams/day and converted into units: 1 unit = 8 grams. Alcohol consumption was then categorized in 1999 as none, 1-2 units/ day, and >2 units/ day. Smoking status was assessed in 1999 by asking whether the subjects smoked currently, in the past or never.
The research nurses, who followed standardized procedures, measured anthropometric data in the form of weight, height and waist circumference in 1989 and 1999. BMI (kg/m2) was calculated from these measurements as body weight divided by the square of standing height. Systolic and diastolic blood pressures were measured twice and means of duplicate measurements were used in all analyses. In 1999 only, non-fasting venous blood samples were analysed for total serum cholesterol concentration and HDL cholesterol with a Bayer DAX-72 analyser. Total cholesterol concentration was determined by enzymatic CHOD-PAP. Phosphotungstic Mg2+ was used to establish HDL cholesterol. LDL cholesterol was calculated by Friedewald formula: LDL-C = Total cholesterol − HDL cholesterol − LDL cholesterol − (triglyceriden/2.2) (in mg/dl)(Gazi et al. 2006).
Descriptive data were presented as means and standard deviation (SD) or median and interquartile range (IQR) for continuous variables and as percentages for categorical variables for men and women separately. Variations in meat consumption between men and women, between years, between regions and occupational social classes were compared using one-way analysis of variance (ANOVA).
Processed meat and red meat were divided into thirds, based on the mean intake per day in 1989 and 1999 of these meat categories. Differences in health outcomes were compared for the different subgroups (low, middle, high consumption) within the meat categories by using one-way analysis of variance (ANOVA) with post hoc Bonferroni tests.
Multiple linear regression analysis was carried out to investigate associations between meat consumption in 1989 and 1999, as a continuous variable, and health outcomes in 1999. Regression analysis was carried out to determine associations with serum cholesterol, blood pressure, BMI and waist circumference after adjustment for potential confounders; total energy intake, alcohol consumption, smoking, region and socio-economic status.
Statistical analyses were carried out by using the statistical software program SPSS version 10.1 for Windows.
Demographic and physical characteristics are shown separately for men and women in table 1. 51.5% of the subjects who had been assessed in 1989 provided blood samples in 1999 and were included in this analysis. Body weight increased in the subjects in this study by more than 5 kg for both men and women between 1989 and 1999. Over 80% of the study population did not smoke in 1999 although 53% of the men and 36% of the women had smoked in the past. Less than a quarter of the sample consumed no alcohol in the assessment period in 1999 but 42% of the men and 15% of the women exceeded the recommendation of the British Heart Foundation, as they drank more than 2 units per day.
Table 2 shows the arithmetic mean, median and interquartile range of intakes of red meat and processed meat. Men consumed significantly more red meat and processed meat than women at both ages 43 and 53 years. The intake of red and processed meat was significantly lower in 1999 compared to 1989 in both men and women. There were no significant differences in meat consumption between regions for men or women in 1989 and 1999. Red meat consumption did not differ between social classes in either year but consumption of processed meat was significantly higher in the manual social class in both men (35g/day, manual; 28g/day, non manual; p=0.003) and women (23g/day, manual; 19g/day, non manual; p=0.02) in 1999 only.
Table 3 shows the total, LDL and HDL cholesterol concentrations and blood pressures of the 1152 subjects in 1999. Women had significantly higher mean HDL cholesterol concentration (p=0.002) and lower mean diastolic blood pressure (p<0.005).
Tables Tables44 and and55 show the means of cardiovascular risk factors measured in 1999 across thirds of red meat and processed meat consumed in 1989. There were no significant differences between thirds of meat consumption by men or women. Tables Tables66 and and77 show the means of cardiovascular risk factors measured in 1999 across thirds of red meat and processed meat consumed in 1999. Waist circumference of men was significantly greater in the highest third of red meat consumption. In women, LDL cholesterol, BMI and waist circumference were increased in the high consumers but not significantly. The highest consumers of processed meat, both men and women, had significantly increased waist circumference and BMI, the latter borderline in the men.
Table 8 shows the means of blood pressure, waist circumference and BMI across thirds of combined red and processed meat intake. The highest male consumers of these meats in both 1989 and 1999 had significantly greater BMI and waist circumference. In men only, blood pressure was also significantly higher in those with the greatest consumption of red and processed meats in 1999. Total, LDL and HDL cholesterol concentrations did not differ significantly between thirds of intakes of combined red and processed meat in 1989 and 1999 (results not show).
Regression analyses confirmed that there were no significant associations between weights of red or processed meat consumed in 1989 or 1999 and serum cholesterol concentration and blood pressure measured in 1999. Table 9 shows the significant positive associations that were found between red and processed meat consumption and combined in 1989 and 1999 and BMI and waist circumference in 1999 in both men and women. Results indicated that a 10 gram increase in red meat consumption in 1989 was associated with a 0.3 cm increase in waist circumference of men (p=0.035) and women (p=0.048) in 1999. A similar association was found for consumption of processed meat. Red and processed meat consumed in 1999 was significantly associated with increased BMI in women only. Table 10 shows the associations between combined red and processed meat consumption in 1989 and 1999 and blood pressure in 1999. A significant positive association was found for 1999 meat intake in men only.
This paper examined consumption of red meat and processed meat in 1989 and 1999 in a British birth cohort in relation to CHD risk factors in 1999. We have previously reported that high consumers of processed meat had an unhealthier diet with regard to the key nutrients (Prynne et al. 2007). The results of this study suggest that red or processed meat consumption measured 10 years earlier or synchronously do not predict an increased risk of CVD as indicated by cholesterol concentration or blood pressure. However there were significant positive associations between meat consumption and BMI and waist circumference.
This study used a more accurate estimate of total meat consumption by adding only the meat fraction of mixed or composite dishes to individual meat portions (Prynne et al. 2007). Other strengths of our study were the large sample size, the availability of data across all regions in the UK and the longitudinal study design, which gave us the possibility to predict health in the future based on dietary intakes in the past.
Our study had some limitations. Consumption of meat was self-reported; thus reporting bias might have affected our estimates of the effect. Furthermore, of the subjects from whom we had dietary data in 1989 not all provided physiological data in 1999 and were therefore not included in the study. Of those that were included there were a majority who belonged to non-manual socio-economic classes who may have been more health-aware. Furthermore, when risk factors were measured in 1999 the subjects were 10 years older than when the dietary data were collected in 1989. Changes in cholesterol levels, blood pressure and weight could be due to the ageing population per se or there may have been other dietary factors that changed with age.
This study did not find any significant difference in total, HDL or LDL cholesterol across the categories of red meat and processed meat consumed 10 years earlier or synchronously with the cholesterol measurements. This is in line with several dietary interventions and cross-sectional studies in which no rise in blood cholesterol and LDL cholesterol was found after consumption of red meat (Li et al. 2005). Nicklas et al. also found no differences in total, LDL and HDL cholesterol across quartiles of meat consumption by a group of 504 young adults aged 19-28 years (Nicklas et al. 1995). In an intervention study involving 38 hypercholesterolaemic men consumption of chicken or beef caused a decrease in LDL and total cholesterol and an increase in HDL cholesterol when saturated fat intake was maintained at the same level (Scott et al. 1994) and hypercholesterolaemic men fed a lipid lowering diet had reduced plasma total and LDL cholesterol regardless of whether they ate chicken or beef (Beauchesne-Rondeau et al. 2003). However, in a cross sectional study of young adults Slattery et al. found lower total and LDL cholesterol concentrations in those who ate red meat and poultry less than once a week compared with young adults who consumed meat more frequently (Slattery et al. 1991). These results would seem to imply that meat per se does not have an effect on plasma cholesterol concentrations but it is the dietary pattern associated with the consumption of particular types of meat. The diet associated with the consumption of processed meat in the NSHD had a higher fat content but the fat was not necessarily meat fat (Prynne et al. 2007). Not all saturated fatty acids are equally hypercholesterolaemic; beef fat contains relatively more stearic acid compared to milk fat that contains more myristic and palmitic fatty acids; the latter having greater cholesterol–raising potential (Ulbricht and Southgate 1991).
Previous observational studies reported that dietary patterns characterized by a high intake of red and processed meat were positively associated with systolic and diastolic blood pressure (Ascherio et al. 1996; Miura et al. 2004; Steffen et al. 2005), and vegetarians were reported to have lower blood pressure than the general population (Sacks and Kass 1988). Longitudinal data from the DASH study suggest that a diet low in red meat results in significantly reduced systolic and diastolic blood pressure (Appel et al. 1997). In the NSHD, meat consumption did not predict elevated blood pressure 10 years later but there was a significant rise in systolic and diastolic blood pressure in 1999 associated with a higher intake of red and processed meat combined in men but not women at the same time point. We have previously reported that high consumers of processed meat in the NSHD cohort had significantly higher sodium intakes (Prynne et al. 2007). It is well established that salt intake is associated with increased blood pressure (Law et al. 1991; Khaw et al. 2004) so a relationship between processed meat and blood pressure, if detected, could probably be due to the salt that is added during processing rather than the meat.
Many cross-sectional studies have investigated the relationship between diet patterns and BMI or waist circumference (Togo et al. 2001; Newby et al. 2003; Rosell et al. 2006). There was limited evidence suggesting that a diet low in meat was associated with a lower BMI (Togo et al. 2001). Furthermore, healthy elderly of the US Framingham Heart Study and the European SENECA study who were in the meat and fat cluster tended to have highest waist circumference and BMI. (Haveman-Nies et al. 2001). Our results showed a positive association between intake of red or processed meat and waist circumference measured 10 years later and if red and processed meats were combined there was also a positive association with BMI. Both men and women in the NSHD had reduced total red and processed meat consumption by 1999 compared to 1989 but this was still associated with increased waist circumference and, in women, BMI also.
In conclusion, the results presented did not show that consumption of red or processed meat by the NSHD subjects related to traditional risk factors for CHD. Any relationship between meat consumption and to CHD risk reported from other studies might be from the type of diet of which these foods form a part; i.e. a diet containing high levels of saturated fat and sodium and, possibly, a low intake of fruit and vegetables. This is recognised in the COMA report which recommended that the intake of red meat should not be reduced but eaten trimmed of fat (Department of Health 1994). It did recommend that the intake of meat products be halved in order to reduce fat and sodium intakes and that vegetable and fruit consumption be increased. The members of the 1946 birth cohort in 1999 would appear to have heeded that advice as their total fat intake was reduced and they consumed less processed meat but increased fruit and vegetables compared to 1989 (Prynne et al. 2005; Prynne et al. 2007). These subjects were 53 years of age in 1999, an age when health and mortality becomes more immediately pertinent, so our findings may not be able to be extrapolated to the general population of the UK. More prospective studies of wider population groups are needed with careful and accurate estimations of meat consumption to answer these questions conclusively.
Sponsorship: This work was supported by the UK Medical Research Council.
JW acknowledges the support she received from the Netherlands Heart Foundation for her internship in Cambridge.