Half were randomly assigned to get a high-dose vitamin D supplement; the other half got a dummy pill on the same schedule.
At the end of the study, those getting 100,000 international units (IU) of vitamin D each month had improvement in respiratory muscle strength and could exercise longer and more intensely than those who were not getting vitamin D.
“I think it’s important,” says study researcher Miek Hornikx, physiotherapist and doctoral student in the department of pneumology at the Katholieke Universiteit Leuven in Leuven, Belgium. “But more studies are needed, mainly to look at the mechanisms by which vitamin D can improve muscular function."
The study was presented at the 2011 American Thoracic Society International Conference in Denver.
Studies show that people with COPD often have low levels of vitamin D, a vitamin best known for its role in keeping bones strong.
A 2010 report in the journal Thorax, for example, found that 60% of patients with severe COPD and 77% with very severe COPD had blood levels of vitamin D under 20 ng/mL, a level experts say is insufficient.
Some of the cause may be inherited. Certain gene variants have been shown to increase the risk of having low vitamin D levels.
But many experts think people with COPD may have low levels of vitamin D simply because they get less sun.
The body uses UV rays from sunlight to manufacture vitamin D.
“Getting outside is hard if you’re sick,” says Kevin K. Brown, MD, vice chairman of the department of medicine at National Jewish Health in Denver.
Vitamin D’s benefits may extend well beyond bone health. It has also been shown to play a role in muscle health. Low levels have been shown, for example, to be associated with an increased risk of falls in men and slower walking speeds and poorer balanced in women.
“Since vitamin D is often depleted in patients with COPD, we wanted to see if vitamin D supplementation would have a beneficial effect on rehabilitation among these patients, perhaps by increasing muscle strength,” Hornikx says.