Low Vitamin D Associated with Worse Asthma

Low levels of vitamin D in asthma patients are associated with reduced lung function and less response to steroid medications, according to researchers at National Jewish Health.

"Our findings suggest that vitamin D plays a significant role in asthma severity and response to treatment," said Rand Sutherland, MD, MPH, Chief of the Pulmonary Division at National Jewish Health. "This raises the possibility that vitamin D supplementation in asthma patients with low levels of vitamin D may improve their asthma."

The researchers published their findings online today in the American Journal of Respiratory and Critical Care Medicine.

Vitamin D has long been recognized as essential for bone health. Recently, it has been associated with a variety of benefits ranging from fighting colds to cancer. However, several reports have indicated that people are actually getting less vitamin D than they used to, often resulting in lower blood levels than the 30 nanograms per milliliter (ng/mL) generally considered healthy.

Inhaled steroids are the most effective controller medication for asthma, helping the majority of patients control their disease. However, individual patients respond differently to the medications, and a substantial number do not achieve optimal control despite high doses of inhaled steroids. Some evidence has suggested that vitamin D might play a role in response to steroids.

The researchers evaluated 54 adults with persistent asthma. They found that higher levels of vitamin D were associated with better lung function; patients could exhale 21 more milliliters of air in one second for each ng/mL increase in vitamin D levels. Patients with vitamin D levels below 30 ng/mL had airways that were almost twice as sensitive to the airway irritant methacholine, commonly used to evaluate the likelihood of airway constriction, as patients with vitamin D levels above 30 ng/mL. In cells taken from the patients, higher levels of vitamin D were associated with increased responsiveness to the steroid dexamethasone.

The researchers also found that higher body mass was associated with lower vitamin D levels, suggesting that overweight and obese asthmatics may be likely to experience the consequences of low vitamin D.

"Our findings suggest that vitamin D levels influence a number of important features of asthma, including lung function, bronchospasm and therapeutic response to steroids," said Dr. Sutherland. "The next question to answer is whether giving supplemental vitamin D will lead to clinical improvements in patients with asthma. We are developing prospective studies to answer that."