Nutritional Factors and Coronary Heart Disease
Alberto Ascherio, MD, Dr.PH.
Associate Professor of Nutrition and Epidemiology, Harvard School of Public Health, Boston, MA, USA.
Once dominated by the classic diet-heart hypothesis, the debate on diet and coronary disease has recently expanded to include several new hypotheses. Pivotal to this change have been the results of ongoing large prospective epidemiological investigations and the interaction of epidemiologists with laboratory scientists. Epidemiological investigations with repeated and validated dietary measurements are now about to reach their maturity. The Nurses Health Study -- an investigation of female nurses in the United States -- is approximating 20 years of follow-up since the first dietary assessment; dietary information has been update every four years so that it is now possible to conduct dynamic analysis that take into account changes in diet over time. A similar cohort of men is only six years behind. The availability of blood samples in both cohorts will also allow a better understanding of the role of several biomarkers, and the investigation of genes and gene-environment interactions. The results of these investigations have provided strong and direct evidence that high intakes of vitamin E, fiber, and folic acid reduce the risk of coronary disease. Other hypotheses, however, such as the widely accepted idea that high total fat intake increases the risk of coronary disease, have not been corroborated. Rather, individual fatty acids seem to have different associations with risk of CHD, that are only in part explained by their known metabolic effects. For example, there is growing evidence that intake of trans-unsaturated fatty acids increase the risk of coronary disease more strongly than predicted by its adverse on the ratio of LDL cholesterol to HDL cholesterol. On the other hand, the results of most epidemiological investigations are consistent with beneficial effects of small amounts of alpha-linolenic acid, although the mechanisms of this potential effect remain unknown. In the future, an interaction between epidemiological and laboratory research will be increasingly important. Since long term randomized trials in humans are often unfeasible, sound conclusions on the health effects of  nutritional factors will have to rest on strong epidemiological evidence and a coherent body of laboratory results.