Back to Journals » Nutrition and Dietary Supplements » Volume 2

The effect of β-carotene on common cold incidence is modified by age and smoking: evidence against a uniform effect in a nutrient–disease relationship

Authors Hemila H

Published 12 October 2010 Volume 2010:2 Pages 117—124

DOI https://doi.org/10.2147/NDS.S13299

Review by Single-blind

Peer reviewer comments 2


Harri Hemilä
Department of Public Health, University of Helsinki, Helsinki, Finland

Background: Analyses in nutritional epidemiology usually assume that there is a uniform effect a nutrient. The purpose of this study was to test whether the effect of ß-carotene on common cold incidence is uniform over the population.
Methods: The Alpha-Tocopherol Beta-Carotene Study, which recruited male smokers aged 50–69 years, was conducted in Finland in 1985–1993. The active follow-up lasted for 4.7 years (mean). This analysis is restricted to the β-carotene and placebo arms (n = 14,569). The rate ratio (RR) of the common cold was modeled as a function of age at follow-up in the β-carotene arm compared with the placebo arm using Poisson regression.
Results: Separate regression models in four subgroups of participants were constructed on the basis of the age of smoking initiation (≤20 years versus ≥21 years) and baseline smoking level (5–14 versus ≥15 cigarettes/day). In three of the four subgroups, the effect of β-carotene was significantly modified by age. Among participants older than 70 years, the extent of smoking modified the effect so that β-carotene increased the incidence of colds in those who started smoking at an early age and smoked heavily: RR = 1.16 (95% confidence interval [CI]: 1.02–1.33), but decreased the incidence in those who started smoking at a later age and smoked less: RR = 0.76 (95% CI: 0.61–0.94).
Conclusions: The strong evidence of heterogeneity in the β-carotene effect on the incidence of colds challenges the validity of cohort studies on nutrients, because they are usually based on the assumption of a uniform effect of the nutrient over the studied population.

Keywords: antioxidants, dietary supplements, male, randomized controlled trial, respiratory infections

Creative Commons License This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution - Non Commercial (unported, v3.0) License. By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms.

Download Article [PDF]