Vitamin D in pulmonary disease.

There is growing interest in the role of vitamin D in respiratory disorders. Its action as the main regulator of calcium and bone metabolism is well established, but vitamin D is also thought to influence inflammation, immunity and host defence. Accumulating evidence associates vitamin D insufficiency with poorer respiratory outcomes. This narrative review summarises the current literature on the role of vitamin D in inflammatory mechanisms associated with asthma, COPD, interstitial lung disease, lung cancer, tuberculosis and acute respiratory tract infections. It outlines the existing evidence supporting the immunomodulatory and anti-inflammatory effects of vitamin D in respiratory disease. Results from the current literature are mixed, with clinical trial data not always aligning with a plausible mechanistic rationale or data from observational studies. Future large randomised controlled trials, targeting vitamin D deficient cohorts and assessing outcomes over longer durations are needed to provide clarity on the clinical utility of vitamin D supplementation in respiratory disease.