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In the overall analysis, vitamin E use did not affect the odds of tuberculosis in smokers. In people who smoked at least 20 cigarettes per day and consumed diets high in vitamin C, however, vitamin E supplements more than doubled the risk.
Vitamin E is a widely used dietary supplement believed to enhance immune function, note authors Dr Harri Hemila and Dr Jaakko Kaprio. However, trials in human subjects have shown unpredictable effects of vitamin E on various infectious diseases.
How the study was conducted
To examine the impact of vitamin E use on the risk of tuberculosis, the two researchers from the University of Helsinki in Finland analysed data from the ATBC (Alpha-Tocopherol, Beta-Carotene Cancer Prevention) Study.
The study participants were 29 023 male smokers, ages 50 to 69 years, who were randomly assigned to take daily supplements containing vitamin E, beta-carotene, vitamin E plus beta-carotene, or inactive placebo.
During a follow-up period of around 6 years, 174 cases of tuberculosis were diagnosed. Overall, neither vitamin E nor beta-carotene supplements affected the risk of tuberculosis.
Risk more than doubled
However, as noted, the combination of smoking 20 or more cigarettes per day and consuming a diet rich in vitamin C and vitamin E supplements more than doubled the risk of tuberculosis. Further analysis showed that the increased risk was restricted to the first year after vitamin E supplementation began.
"Although vitamin E may be beneficial in restricted population groups, those groups are poorly defined so far," Hemila and Kaprio point out.
"The consumption of vitamin E supplements by the general population should be discouraged because there is evidence of harm for some people," they conclude.
SOURCE: British Journal of Nutrition, online February 18, 2008. – (Reuters Health)
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