Are geographical differences in cardiovascular mortality due to morbidity differences or to methodological differences? The project "myocardial infarction in Mid-Sweden"

The diet-heart disease hypothesis: a response to Atrens

In a recent examination of the main tenets of the widely accepted diet-heart disease hypothesis, Atrens concluded that the evidence to date is not sufficient to support the hypothesis. Reviewing Atrens' critique highlights both strengths and limitations in his case against the role of dietary lipids and cholesterol in coronary heart disease mortality. Research on the following hypothesized relationships is discussed in light of the objections raised by Atrens: the relationships between fat intake and heart disease mortality; dietary fat and serum cholesterol; serum cholesterol and atherosclerosis; atherosclerosis and heart disease death; and serum cholesterol and heart disease death. The inconsistency of the findings suggests that definitive answers regarding the diet-heart disease hypothesis are premature and that the polarized positions of acceptance vs rejection of the hypothesis fail to account for the full range of results.

The questionable wisdom of a low-fat diet and cholesterol reduction

The prevalent wisdom that a low-fat diet and cholesterol reduction are essential to good cardiovascular health is coming under increased scrutiny. An examination of the foundations of this view suggests that in many respects it was ill-conceived from the outset and, with the accumulation of new evidence, it is becoming progressively less tenable. Cross-sectional, longitudinal and cross-cultural investigations have variously suggested that the relationship between dietary fat intake and death from heart disease is positive, negative and random. These data are incompatible with the view that dietary fat intake has any causal role in cardiovascular health. Although hypercholesterolemia is associated with increased liability to death from heart disease, it is as frequently associated with increased overall life expectancy as with decreased life expectancy. These findings are incompatible with labelling hypercholesterolemia an overall health hazard. Moreover, it is questionable if the cardiovascular liability associated with hypercholesterolemia is either causal or reversible. The complex relationships between diet, serum cholesterol, atherosclerosis and mortality and their interactions with genetic and environmental factors suggest that the effects of simple dietary prescriptions are unlikely to be predictable, let alone beneficial. These cautions are borne out by numerous studies which have shown that multifactorial primary intervention to lower cholesterol levels is as likely to increase death from cardiovascular causes as to decrease it. Importantly, the only significant overall effect of cholesterol-lowering intervention that has ever been shown is increased mortality. The stress and helplessness associated with misapprehensions as to the dangers of dietary fat and the asceticism inherent in the war on cholesterol have considerable implications for health practices. Recent research in behavioral immunology suggests that stress and helplessness are likely to compromise immunity and promote ill-health.

Genetic susceptibility to death from coronary heart disease in a study of twins

BACKGROUND

A family history of premature coronary heart disease has long been thought to be a risk factor for coronary heart disease. Using data from 26 years of follow-up of 21,004 Swedish twins born between 1886 and 1925, we investigated this issue further by assessing the risk of death from coronary heart disease in pairs of monozygotic and dizygotic twins.

METHODS

The study population consisted of 3298 monozygotic and 5964 dizygotic male twins and 4012 monozygotic and 7730 dizygotic female twins. The age at which one twin died of coronary heart disease was used as the primary independent variable to predict the risk of death from coronary heart disease in the other twin. Information about other risk factors was obtained from questionnaires administered in 1961 and 1963. Actuarial life-table analysis was used to estimate the cumulative probability of death from coronary heart disease. Relative-hazard estimates were obtained from a multivariate survival analysis.

RESULTS

Among the men, the relative hazard of death from coronary heart disease when one's twin died of coronary heart disease before the age of 55 years, as compared with the hazard when one's twin did not die before 55, was 8.1 (95 percent confidence interval, 2.7 to 24.5) for monozygotic twins and 3.8 (1.4 to 10.5) for dizygotic twins. Among the women, when one's twin died of coronary heart disease before the age of 65 years, the relative hazard was 15.0 (95 percent confidence interval, 7.1 to 31.9) for monozygotic twins and 2.6 (1.0 to 7.1) for dizygotic twins. Among both the men and the women, whether monozygotic or dizygotic twins, the magnitude of the relative hazard decreased as the age at which one's twin died of coronary heart disease increased. The ratio of the relative-hazard estimate for the monozygotic twins to the estimate for the dizygotic twins approached 1 with increasing age. These relative hazards were little influenced by other risk factors for coronary heart disease.

CONCLUSIONS

Our findings suggest that at younger ages, death from coronary heart disease is influenced by genetic factors in both women and men. The results also imply that the genetic effect decreases at older ages.

Traditional risk-factor profile fails to explain striking geographical differences in IHD mortality among middle-aged men. The project "myocardial infarction in mid-Sweden"

An east-west gradient in cardiovascular mortality has been reported from the region of mid-Sweden. Postal questionnaire studies found that the risk factor distributions among middle-aged men were similar in areas with striking differences in cardiovascular mortality. In this study, 120 randomly selected 50-year-old men in two high mortality communities in the west and 120 men from two low mortality communities in the east were invited to a health survey in which serum lipids and other risk factors were analysed. Total serum cholesterol, LDL-cholesterol, HDL-cholesterol, and triglyceride levels were similar. Among fatty acids, stearic acid was high and arachidonic acid was low in the high mortality area. The levels of other traditional risk factors were the same. After taking these differences into account, the mortality differences remain large.