Vitamin D link to lung function in smokers

Vitamin D levels seem to determine the rate of lung function decline among smokers, the results of an American study show.

Researchers found that the effect of smoking on lung function decline was greater in vitamin D-deficient participants than in those whose vitamin D level reached the recommended levels.

"Our results suggest that vitamin D might modify the damaging effects of smoking on lung function. These effects might be due to vitamin D's anti-inflammatory and anti-oxidant properties," said lead author, Nancy Lange (Harvard Medical School, Boston, Massachusetts, USA).

The study included 626 White, male participants enrolled in the Normative Aging Study between 1984 and 2003, with an average age of 73 years. A quarter had vitamin D deficiency (VDD; 25-hydroxyvitamin D, ≤ 20 ng/ml) and the average number of cigarette pack-years per person was 20.3. Participants had their vitamin D levels and lung function measured at three time points during the 20-year period.

At the final time point, vitamin D levels were not associated with lung function in the overall population. However, cross-sectional analysis showed vitamin D deficiency exacerbated the impact of smoking on spirometry measurements.

The authors found that for each additional pack-year, mean forced expiratory volume in 1 second (FEV₁) was reduced by 12 ml in those with VDD compared with 6.5 ml in vitamin D-sufficient participants.

Furthermore, having the same number of pack-years smoking history led to a significantly faster yearly decline in FEV₁ in vitamin D-deficient than in vitamin-D sufficient participants.

The results support those of previous epidemiologic studies showing a link between lung function and vitamin D levels. Several reasons for a potential interaction between vitamin D and lung function have been suggested, including effects on viral-induced inflammation, rates of respiratory infections, and an anti-oxidant effect.

The authors say that their results will need to be verified in more diverse study populations but, if confirmed, could have major public health implications, and vitamin D supplementation could be recommended for smokers. However, the American Thoracic Society's Tobacco Action Committee pointed out that quitting smoking is likely to be far more beneficial to health.

Chair, Alexander White, said: "First and foremost, patients who smoke should be fully informed about the health consequences of smoking and in addition be given all possible assistance to help them quit smoking."

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