Environmental tobacco smoke and ischaemic heart disease: a case study in applying causal criteria

We use Bradford Hill criteria to synthesize the biological and epidemiologi cal literature so as to assess formally whether ischaemic heart disease (IH D) is caused by exposure to environmental tobacco smoke (ETS). For the gene ral population we find, at best, weak support for causality: of nine tests, one (biological plausibility) is supported, though not unarguably; three ( strength, consistency, specificity) fail; and five (biological gradient, ex perimental evidence, temporality, coherence, analogy) have insufficient dat a for clear evaluation. For the population with pre-existing IHD the biolog ical support is possibly stronger. We identify three areas for future resea rch: epidemiological studies of those subpopulations with pre-existing IHD; evaluation of the nature of vessel wall thickenings occurring in experimen tal studies; and long-term animal studies of initiation of IHD, including d irect assessment of effects on the accumulation of lipid in vessel walls, a t appropriate ETS levels.