Low vitamin D levels do not increase the risk of chronic obstructive pulmonary disease
Vitamin D levels are not related to acute exacerbations of chronic obstructive pulmonary disease (AECOPD) in patients with severe COPD, according to a large prospective cohort study involving 973 North American patients. The findings were published online ahead of the print edition of the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.
In the study, a secondary analysis of data from a randomized, controlled trial of the effects of azithromycin on the frequency of AECOPD, no relationship was found between baseline Vitamin D levels and time to first AECOPD or between vitamin D levels and AECOPD exacerbation rates.
"Vitamin D insufficiency and deficiency are common in patients with COPD, and patients with severe COPD are at the highest risk for exacerbations, so we hypothesized that low vitamin D levels might increase the risk of AECOPDs," said Ken M. Kunisaki, M.D., of the Minneapolis Veterans Affairs Medical Center. "Our negative results are in contrast with earlier studies in which lower vitamin D levels were associated withhigher rates of respiratory infections in adults and more frequent asthma exacerbations in children."
In the current study, mean forced expiratory volume in one second (FEV1) was 1.12L, 40% of predicted. Mean vitamin D level at baseline was 25.7 ± 12.8 ng/mL, with 33.1% of subjects categorized as vitamin D insufficient (≥20 ng/mLbut <30 ng/mL), 32.0% as vitamin D deficient (<20 ng/mL) and 8.4% as having severe vitamin D deficiency (<10 ng/mL).AECOPDs were defined as a complex of respiratory symptoms (increased or new-onset) of at least 1 of thefollowing: cough, sputum, wheezing, dyspnea, or chest tightness with a durationof at least 3 days and requiring treatment with an antibiotic or systemiccorticosteroid.
During 1 year of follow-up, study subjects experienced a total of 1415 AECOPDs. Of 973 patients,360 (37%)remained AECOPD-free, 278 (29%) had 1 AECOPD, 133 (14%)had 2 AECOPDs, and 202 (21%) had 3 or moreAECOPDs.
In the primary analysis, vitamin D levels had no relationship to time to first AECOPD; for a 10 ng/mL increment in vitamin D level, the estimated hazard ratio was 1.04 (95% confidence interval: 0.97-1.12). In secondary analyses, vitamin D levels were not related to annualized rates of AECOPDs in either Poisson (p=0.82)or negative binomial analyses (p=0.87).
Patients with severe vitamin D deficiency had a higher mean rateof AECOPDs, but this difference was not statistically significant. Patients with severe vitamin D deficiency did not exhibit faster time to first AECOPD than other patients.
The study had some limitations. Vitamin D levels were only assessed at baseline, and so may have changed during the study period. Seasonal changes in vitamin D levels may also have occurred.
"Contrary to what we expected, baseline vitamin D levelswere not related to the risk of subsequent AECOPDs in this large group of COPD patients at high risk of AECOPD," Dr. Kunisaki said. "Vitamin D supplementation is unlikely to have an effect on AECOPD risk in these patients."