Effect of β-Carotene Supplementation on the Risk of Pneumonia Is Heterogeneous in Males: Effect Modification by Cigarette Smoking.

Beta-carotene has been suggested to be a factor for improving the immune system, which implies that it might decrease the risk of infections. We therefore analyzed whether beta-carotene supplementation influenced pneumonia risk in 14,564 Finnish male smokers of the Alpha-Tocopherol Beta-Carotene (ATBC) Study. There were 231 pneumonia cases in the beta-carotene group and 217 cases in the placebo group. Thus, beta-carotene had no effect on the average incidence of pneumonia, RR=1.07 (95% CI: 0.89-1.29). However, cigarette smoking exposure significantly modified the effect. Beta-carotene increased pneumonia risk by RR=4.0 (95% CI: 1.63-10) among 990 participants who started to smoke at the age of ≥21 y and smoked ≥21 cigarettes per day at the study baseline. However, beta-carotene had no influence on pneumonia risk for the remaining participants. We also analyzed the effect of beta-carotene on participants who quit smoking during the ATBC Study. Among 4,290 participants who quit smoking, the 58 pneumonia cases were evenly distributed between the beta-carotene and placebo groups with RR=0.93 (95% CI: 0.55-1.55). Accordingly, no evidence was found that beta-carotene decreased pneumonia risk; instead, it significantly increased the incidence of pneumonia in a subgroup that covered 7% of the study population.