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Mechanisms and Biomarkers (WG 4) page 6
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outcomes. Problems have also arisen in the parallel and often independent development of
free radical and epidemiology research. Large scale intervention trials initiated in the late
1980’s to evaluate ß-carotene, vitamin E and retinol were seriously compromised when it was
found that excessive ß-carotene consumed by high risk groups (male Finnish smokers ATBC
study) resulted in an 18% increase in cancer incidence compared to placebo group. The effect
of supplemental synthetic β-carotene was even more pronounced in the aborted U.S. CARET
study where smokers receiving β-carotene and retinol had a 28% increase in the incidence of
lung cancer compared to the control group. These were classic mistakes of misinterpreting
association for causation and have been the major confounding influences in this field of
research. Intervention trials can also miss important factors, if for example supplementation is
in a well-nourished rather than a poorly nourished group (Esterbauer et al., 1997). Protective
properties might also be missed if the supplementation dose is too small or too large. In light
of previous experience future intervention trials should be designed to take account of the
behaviour of test compounds in relevant in vivo models.