Abstract
Background: The impact of low vitamin D status on the development of asthma is not clear. We conducted a nested case-control study to investigate the relation of baseline serum 25-hydroxyvitamin D [25(OH)D] levels and adult-onset asthma.
Methods: A total of 25,616 adults aged 19-55 years who participated in the second Norwegian Nord-Trøndelag Health Study (HUNT), were followed-up for 11 years. A nested case-control study consisted of all the new onset asthma cases during the follow-up (n=600) and a random sample of non-asthma controls (n=2013). Baseline blood samples were available in 584 asthma cases and 1958 non-asthma controls. Baseline serum 25(OH)D levels were measured by automated antibody-based chemiluminescence assay.
Results: The mean level of baseline serum 25(OH)D was slightly lower in asthma cases compared with controls in both men (geometric mean: 51 vs. 54 nmol/L, p=0.04) and women (geometric mean: 52 vs. 55 nmol/L, p=0.02). Men with a serum 25(OH)D levels <50 nmol/l at baseline had a significantly higher risk of asthma (crude OR 1.75, 95%CI 1.14-2.68) compared with those with a serum 25(OH)D level of 75 nmol/l or higher. After adjustment for age, smoking, family history of asthma, education, physical activity, social benefit, and economic difficulties, the OR was 1.60 (95% CI 1.02-2.50). Further adjustment for body mass index (BMI) yielded an OR of 1.47 (95%CI 0.93-2.32). In women, baseline serum 25(OH)D level was not associated with the risk of asthma in either unadjusted or adjusted models.
Conclusions: After adjustment for BMI and other covariates, baseline levels of serum 25(OH)D were not independently associated with adult-onset asthma.
- © 2011 ERS
