Dietary intake and supplement use of vitamins C and E and upper respiratory tract infection.

OBJECTIVE: Antioxidants are regulators of immune function and may play a role in upper respiratory tract infections (URTI). We investigated the potential effects of dietary intake from food and supplement use of vitamins C and E on the risk of self-reported URTI. METHODS: We conducted a population-based cohort study of 1509 Swedish men and women ages 20 to 60 with a follow-up period of 4 months. Participants reported a total of 1181 occurrences of URTI. Poisson regression model was used to control for age, sex, and other confounding factors. RESULTS: Among women, we found that the incidence rate ratio (IRR) for high intake of vitamin C (>200 mg/d) from food was 0.69 (95% CI 0.49-0.98) compared with low intake (<100 mg/d). This association was not seen among men, for whom the IRR was 1.16 (95% CI 0.79-1.70) for high intake of vitamin C (>150 mg/d) compared with low intake (<50 mg/d). We saw no protective effect of vitamin E from food among either men or women, but a possible protective effect of vitamin C and E supplement use among men (vitamin C, 0.69 [95% CI 0.47-1.02]; vitamin E, 0.56 [95% CI 0.33-0.95]), although not among women. CONCLUSION: The present study is the first observational study to suggest that intake of vitamin C from food is sufficient to lower the risk of URTI among women. In addition, it appears that supplement use of vitamin E and vitamin C may reduce the risk of URTI among men, who overall had a lower intake of vitamin C from food than women.