Are these cross-cultural associations causal?
Ecological or cross-cultural associations are frequently viewed as the lowest level of evidence about causality. However, to demean ecological associations is to fail to recognize the powerful indication they provide about the population burden of disease – and thus the potential for prevention – when correlations among populations are congruent with sound clinical evidence, with significant correlations at the level of individuals within populations, and with known mechanisms.
In the SCS, the average population intake of saturated fat was based on chemical analysis of duplicate portions of foods consumed as collected from sampled families, while serum cholesterol data were collected at baseline and CHD incidence verified prospectively. The differences in average serum cholesterol level among the seven countries cohorts could in large part be ascribed to differences in average saturated fat intake and were in accord with results of controlled dietary experiments.
The average population serum cholesterol levels at baseline were strongly related to 5- and 10-year CHD incidence rates and were in good accord with results of randomized trials in which the effect of replacement of saturated by polyunsaturated fat on CHD incidence was investigated as well as with those of trials on the serum cholesterol-lowering effect of statins. Based on the congruence and totality of evidence from prospective observational studies and cholesterol-lowering trials, we conclude that the associations found among saturated fat intake, serum cholesterol level and CHD incidence are causal.