Vitamin D status and longitudinal lung function decline in the Lung Health Study.

Area of Science:

• Pulmonary Medicine
• Nutritional Science
• Epidemiology

Background:

• Low blood vitamin D levels are suspected to increase the risk of poor lung function, primarily based on cross-sectional studies.
• Vitamin D deficiency and insufficiency are prevalent, particularly in winter, affecting a significant portion of the population.

Purpose of the Study:

• To investigate the longitudinal relationship between baseline plasma 25-hydroxyvitamin D (25(OH)D) and the rate of lung function decline in smokers.
• To test the hypothesis that lower baseline 25(OH)D levels are associated with more rapid lung function decline.

Main Methods:

• A nested, matched case-control study was conducted within the Lung Health Study 3 cohort.
• Cases (rapid lung function decline) and controls (slow lung function decline) were continuous smokers, matched for phlebotomy date and clinical center.
• Baseline plasma 25(OH)D levels were compared between cases and controls over approximately 6 years of follow-up.

Main Results:

• Despite significant differences in the rate of forced expiratory volume in 1 second (FEV1) decline between rapid and slow decliners (-152 vs. -0.3 mL·yr⁻¹), there was no significant difference in baseline 25(OH)D levels (25.0 vs. 25.9 ng·mL⁻¹).
• A high prevalence of vitamin D insufficiency (35%) and deficiency (31%) was observed, with only 4% having normal levels in winter.
• Baseline 25(OH)D levels were not found to be predictive of subsequent lung function decline.

Conclusions:

• Vitamin D insufficiency and deficiency are common among continuous smokers with established mild-to-moderate chronic obstructive pulmonary disease (COPD).
• Baseline plasma 25(OH)D levels do not predict the rate of lung function decline in this population.
• The findings challenge the postulated link between low vitamin D and accelerated lung function decline in smokers with COPD.