Why heart disease mortality is low in France: the time lag explanation.

In France mortality from ischaemic heart disease is about a quarter of that in Britain. The major risk factors are no more favourable in France, and this so called “French paradox” has not been satisfactorily explained. Table 1 shows the difference in mortality from heart disease between the countries, and table 2 shows the similar levels of animal fat consumption, serum total cholesterol and high density lipoprotein cholesterol concentrations, blood pressure, and (in men) smoking. The French paradox is usually attributed to the higher consumption of alcohol in France, notably of wine, and some have suggested a specific effect of red wine. In this article we assess quantitatively the extent to which this and other possible explanations can account for the low rate of heart disease in France. We then consider a novel “time lag” hypothesis, which, we believe, is the main explanation for the paradox. This hypothesis arises from the observation that animal fat consumption and serum cholesterol concentration have been similar in France and Britain for a relatively short time—about 15 years. For decades up to 1970, France had lower animal fat consumption (about 21% of total energy consumption v 31% in Britain) and serum cholesterol (5.7 v 6.3 mmol/l), and only between 1970 and 1980 did French values increase to those in Britain. 12–25 There must be a time lag between the increase in serum cholesterol concentration and the full effect of the resulting increase in coronary artery atheroma and risk of death from ischaemic heart disease. The observations that Western populations are exposed to high levels of dietary saturated fat and serum cholesterol from childhood, that atheroma progresses slowly throughout life, and that only about 1% of men die from ischaemic heart disease before the age of 50 suggest that decades of exposure must elapse. We propose that this is the main explanation for the low mortality from ischaemic heart disease in France. A similar time lag is recognised with smoking and lung cancer, in which it is the smoking habit of 30-40 years ago that is important in determining current risk, and a long incubation period for heart disease has been previously proposed.