To the Editor: Dr Bjelakovic and colleagues1 showed that there is no evidence from randomized trials that antioxidant supplements reduce mortality. However, the authors did not consider that the effects might vary among different population subgroups so that an average for a large group of people could be misleading.
Analyses of the large-scale Alpha-Tocopherol Beta-Carotene (ATBC) Cancer Prevention Study found substantial divergence in the effect of 50 mg/d of vitamin E on common cold incidence in elderly men. Among participants 72 years or older, who smoked heavily, and lived outside cities, use of vitamin E increased common cold incidence by 58% (95% confidence interval [CI], 23%-101%; 0.83 vs 0.53 colds per year), whereas in less-smoking city-dwellers it reduced common cold incidence by 46% (95% CI, –20% to –63%; 0.47 vs 0.86 colds per year).2 The effect of vitamin E on the incidence of pneumonia also diverged so that the risk increased or decreased depending on the age of smoking initiation.3 Furthermore, among participants who exercised during leisure, vitamin E reduced the incidence of pneumonia by 50% (95% CI, –16% to –70%; 1.5 vs 3.0 cases of pneumonia per 1000 person-years); however, the number needed to treat was high, so that 667 people would need to take vitamin E for one year to prevent one episode of pneumonia.4 Although the practical significance of these findings is uncertain, they indicate that subgroups of people may benefit, or may be harmed from vitamin E supplementation even though the average effect in the population is nil.
Hemilä H. Antioxidant Supplements and Mortality. JAMA. 2007;298(4):400-403. doi:10.1001/jama.298.4.401-a