Vitamin D and Lung Function Decline in Adults With Asthma

We investigated whether low 25-hydroxyvitamin D (25(OH)D) levels were associated with more lung function decline in adults with asthma and whether this association was modified by smoking status or inhaled corticosteroid (ICS) use. We analyzed data on 395 adults with asthma from the Nord-Trondelag Health Study (1995-2008), Norway. Plasma 25(OH)D and lung function were measured at baseline, and lung function measurements were repeated at follow-up, approximately 11 years later. Linear regression was used to estimate lung function decline. Participants with low 25(OH)D (< 50 nmol/L) had more decline in lung function measurements for forced expiratory volume in 1 second (FEV1) (388 mL), forced vital capacity (298 mL), and the FEV1/forced vital capacity ratio (3.7%) over the follow-up, compared with those with high 25(OH)D (a parts per thousand yen50 nmol/L) who declined 314 mL, 246 mL, and 3.0%, respectively (P = 0.08, 0.30, and 0.23, respectively). The associations were stronger in never smokers and non-ICS users. In never smokers, low 25(OH)D levels were associated with more decline in FEV1 (445 vs. 222 mL) (P = 0.01). In non-ICS users, low 25(OH)D levels were associated with more decline in FEV1 (467 vs. 320 mL) (P = 0.02). Low serum 25(OH)D levels were weakly associated with more lung function decline in adults with asthma, and stronger associations were observed in never smokers and non-ICS users.