Intake of multivitamin supplements and incident asthma in Norwegian adults: the HUNT study.

Although intake of multivitamin supplements is becoming increasingly popular, the relationship between intake of multivitamin supplements and incident asthma remains unclear. Prospective studies in adults with long-term follow-up are especially scarce. Our objective was to investigate the association between intake of multivitamin supplements and asthma development in Norwegian adults. We followed 16 952 adult subjects from the second survey of the Nord-Trøndelag Health Study (1995-1997) up to 2006-2008, who, at baseline, were free of asthma and provided information on their intake of multivitamin supplements and cod liver oil. Regular intake of multivitamin supplements or cod liver oil was defined as daily intake for ≥3 months during the year prior to baseline. Incident asthma was defined as reported new-onset asthma after the 11-year follow-up. Intake of multivitamin supplements only was associated with an increased odds ratio for incident asthma (OR 1.55, 95% CI 1.12-2.13) after adjustment for a number of common confounding factors (model I). Similar odds ratios were found for intake of cod liver oil only and for intake of both supplements (1.59 and 1.73, respectively). Regular intake of multivitamin supplements was associated with an increased odds ratio for incident asthma in Norwegian adults.