The effect of vitamin E on common cold incidence is modified by age, smoking and residential neighborhood

Background: We have previously found a 28% reduction in common cold incidence with 50 mg/day vitamin E supplementation in a subgroup of the Alpha-Tocopherol Beta-Carotene Cancer Prevention (ATBC) Study cohort: older city-dwelling men (>= 65 years) who smoked only 5-14 cigarettes/day. Objective: To carry out more detailed analyses to explore the modification of vitamin E effect by age, smoking, and residential neighborhood. Methods: We examined the effect of vitamin E on common cold risk in subjects consisting of the placebo and vitamin E arms (n = 14,573) of the ATBC Study, which recruited males aged 50-69 years who smoked >= 5 cigarettes/day at the baseline. The ATBC Study was conducted in southwestern Finland in 1985-1993; the active follow-up lasted for 4.7 years (mean). We modeled common cold risk as a function of age-at-follow-up in the vitamin E arm compared with the placebo arm using linear splines in Poisson regression. Results: In participants of 72 years or older at follow-up, the effect of vitamin E diverged. Among those smoking 5-14 cigarettes per day at baseline and living in cities, vitamin E reduced common cold risk (RR = 0.54; 95% CI 0.37-0.80), whereas among those smoking more and living away from cities, vitamin E increased common cold risk (RR = 1.58; 1.23-2.01). Conclusions: Vitamin E may cause beneficial or harmful effects on health depending on various modifying factors. Accordingly, caution should be maintained in public health recommendations on vitamin E supplementation until its effects are better understood.