Low levels of vitamin D make asthma worse

Asthmatics with low levels of vitamin D may suffer more severely from the disease than patients with sufficient levels of the vitamin, according to a study conducted by researchers from National Jewish Health in Denver and published in the American Journal of Respiratory and Critical Care Medicine.

"Our findings suggest that low vitamin D levels are associated with worse asthma," lead researcher E. Rand Sutherland said.

The researchers measured the vitamin D blood levels of 54 asthma patients, along with their lung function, airway hyper-responsiveness and response to steroid drug treatment.

Airway hyper-responsiveness measures the air passages' tendency to constrict, leading to breathing difficulty.

The researchers found that hyper-responsiveness was twice as high in patients with vitamin D levels below 30 nanograms per milliliter, lung function was worse, and the body responded more poorly to steroid therapy.

In addition, the bodies of people with low vitamin D levels produced more or the immune system signaling chemical TNF-alpha, which increases inflammation.

"It may be that vitamin D is acting as a modifier of the immune system or a modifier of steroid response in ways that are relevant to people with asthma," Sutherland said.

"There is a potential that restoring normal vitamin D levels in people with asthma may help improve their asthma."

The study also showed, consistent with prior studies, that overweight or obese participants were significantly more likely to suffer from vitamin D deficiency. Scientists believe that because fat sequesters vitamin D in the body, people with more body fat need higher levels of the vitamin.

Previous studies have shown that being overweight increases the risk of asthma. The new study suggests that vitamin D might at least in part explain that connection.

Asthma treatment also, in turn, increases the risk of vitamin D deficiency.

"It is ... known that glucocorticoids [steroids used in asthma treatment] increase the destruction of vitamin D, thus making patients with asthma at higher risk for vitamin D deficiency, which in turn decreases lung function and makes their disease worse," said Michael F. Holick, of Boston University.