BMJ 1996;312:1479-1480 (8 June)

Letters

Objective data trials are needed

EDITOR,--Paul Knekt and colleagues' study showing an apparent protective effect of consumption of flavonoids on the risk of coronary death illustrates the pitfalls of such investigations.1 Intake of flavonoids shows the same association with both non-coronary and coronary mortality. It either reduces biological susceptibility to many diseases or it serves as a marker for a complex of sociobehavioural factors associated with the risk of death.

Observational studies of diet and health have two main problems. Firstly, dietary intakes are socially and culturally determined and are confounded with other exposures influencing risk of death. In a recent study showing an apparent protective effect of dietary fibre against coronary disease there was a greater than fivefold difference in smoking across quintiles of fibre intake.2 With strongly correlated exposures, each measured with some error, it is difficult to separate confounded from real associations reliably. Secondly, characteristics of the participants are associated with biased . . . [Full text of this article]


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Relevant Article

Flavonoid intake and coronary mortality in Finland: a cohort study
Paul Knekt, Ritva Jarvinen, Antti Reunanen, and Jouni Maatela
BMJ 1996 312: 478-481. [Abstract] [Full Text]

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