Researchers have found a relationship between emphysema and serum vitamin D levels, suggesting that the vitamin may play a role in modulating lung structure.
The study used data on 498 participants of the ECLIPSE (Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints) study, including 75 smoking and 75 nonsmoking controls, and 116 patients with each chronic obstructive pulmonary disease (COPD) at Global Initiative on Chronic Obstructive Lung Disease (GOLD) stage 2, 3, and 4. Each COPD group included the 58 patients with the most emphysema on computed tomography and the 58 patients with the least emphysema for each GOLD stage.
There was a high prevalence of vitamin D insufficiency and deficiency in the overall cohort, with a mean 25-hydroxyvitamin D (25[OH]D) level of 24.0 ng/mL; 69% had vitamin D insufficiency (<30 ng/mL), 39% had deficiency (<20 ng/mL), and 8.7% had severe deficiency (<10 ng/mL).
As reported by previous studies, forced expiratory volume in 1 second was significantly associated with serum 25(OH)D, but the researchers also found that emphysema negatively correlated with serum 25(OH)D. Both of these relationships were particularly marked among those with the lowest vitamin D levels. However, while they held after adjustment for confounders, they were not significant among patients with COPD.
The team also reports an association between vitamin D levels and scores on the St George’s Respiratory Questionnaire, as well as bronchodilator responsiveness, 6-minute walking distance, and the biomarkers Clara cell secretory protein 16 and surfactant protein D – something the team says should be explored in future studies.
“This study provides evidence supporting the role of vitamin D in COPD by confirming the relationship between vitamin D and airflow,” say authors Stephen Rennard (University of Nebraska Medical Center, Omaha, USA) and colleagues, writing in Respiratory Medicine.
However, they also note that the association may be due to reverse causality as both diet and decreased outdoor activity among COPD patients may alter vitamin D levels.
“COPD as a cause of reduced vitamin D levels is a plausible and untested possibility,” they comment.
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