Dietary antioxidants and the prevention of CHD epidemiological evidence

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A large number of epidemiological studies have evaluated potential relationships between dietary intake of antioxidants and coronary heart disease (CHD). These are summarised in Table 5.1. Among these, the Nurses' Health study,36 included over 87 000 female nurses 34 to 59 years of age, who completed dietary questionnaires that assessed their consumption of a wide range of nutrients, including vitamin E. During follow-up of up to 8 years 552 cases of major coronary disease were documented. As compared with women in the lowest fifth of the cohort with respect to vitamin E intake, those in the top fifth had a relative risk of major coronary disease of 0.66 after adjustment for age and smoking. Further adjustment for a variety of other coronary risk factors and nutrients, including other antioxidants, had little effect on the results. Similarly, the Health Professionals' Follow-up study, among almost 40 000 males of 40-75 years, followed up for four years, showed a lower risk of coronary disease among men with higher intakes of vitamin E.37

Kushi et al. studied over 34000 postmenopausal women with no cardiovascular disease who in early 1986 completed a questionnaire that assessed, among other factors, their intake of vitamins A, E and C from food sources and supplements.38 After 7 years of follow-up, results suggested that in post-menopausal women the intake of vitamin E from food was inversely associated with the risk of death from coronary heart disease. This association was particularly striking in the subgroup of 21 809 women who did not consume vitamin supplements (relative risks from lowest to highest quintile of vitamin E intake, 1.0, 0.68, 0.71, 0.42 and 0.42; P for trend = 0.008). After adjustment for possible confounding variables, this inverse association remained (relative risks from lowest to highest quintile, 1.0, 0.70, 0.76, 0.32 and 0.38; P for trend = 0.004). By contrast, the intake of vitamins A and C was not associated with lower risks of dying from coronary disease.38

On the other hand, a negative result came from the Rotterdam Study in which 4802 participants aged 55-95 years, who were free of myocardial infarction (MI) at baseline and for whom dietary data assessed by a semiquantitative food frequency questionnaire were available, were followed up for 4 years: an association between vitamin C or vitamin E and MI was not observed.39

Other studies have evaluated plasma levels of different antioxidants, such as vitamins E, C and ^-carotene in populations affected or not by CHD. The WHO/ Monica project has been one of the largest studies that have analysed the intake of these vitamins in populations with different incidence of CHD mortality.40 In populations with similar values of serum cholesterol and blood pressure, an inverse correlation between CHD mortality and vitamin E plasma levels was observed; conversely, no relation existed between CHD mortality, and other vitamins. In areas with low and medium coronary mortality, plasma levels of vitamin E were 26-28 ^M, while at sites with most frequent CHD mortality

Table 5.1 Summary of observational studies

Observational studies

Patients' characteristics

Location of study population

Year

Nurses' Health study36

Health

Professionals' Follow-up study3

Kushi et al.38

87245 female nurses 34-59 years of age, followed up for 8 years

Male, health professionals 40-75 years, followed up for 4 years

34000 postmenopausal women, followed up for 7 years

USA, multicentre

USA, multicentre

USA, multicentre

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