TUESDAY, Jan. 17 (HealthDay News) -- Vitamin D supplements don't seem to help most patients suffering from chronic obstructive pulmonary disease (COPD), according to a new study by Belgian investigators.

Emphysema and chronic bronchitis are the two main forms of COPD, and many sufferers have both. The condition makes it hard for people to breathe.

Since most COPD patients are vitamin D deficient and vitamin D helps fight inflammation, the hope was that high doses of the sunshine vitamin would reduce the number of severe flare-ups ("exacerbations") that can land patients in the hospital, researchers said.

"There are studies showing that patients with vitamin D deficiency are more susceptible to different inflammatory, infectious and autoimmune diseases, and most likely COPD," said lead investigator Dr. Wim Janssens, from the respiratory division at University Hospital Gasthuisberg in Leuven.

However, this study found only a limited benefit from vitamin D supplementation, he said.

"Vitamin D restoration to normal levels in COPD patients does not reduce the number of exacerbations, does not reduce the infections and inflammation," Janssens said.

However, it had an effect on patients with the lowest vitamin D levels, he said. "These patients had benefit from supplementation in terms of exacerbations," he said.

"But this does not allow us to conclude that we need to give all COPD patients these high doses of vitamin D; it just strengthens us in the idea that severe deficiency many enhance inflammation in COPD," Janssens said.

"New studies are needed to confirm what we found," he added.

The report was published in the Jan. 17 issue of the Annals of Internal Medicine.

For the study, Janssens' team randomly assigned 182 patients with moderate to very severe COPD to 100,000 IU (international units) of vitamin D supplements or placebos every month for one year.

Over that time, researchers looked for the rate of flare-ups and hospitalizations as well as quality of life and deaths.

Although blood levels of vitamin D rose significantly in those taking the supplement, there was no significant difference in the time to a first exacerbation or the number of flare-ups between these patients and those receiving placebos, the researchers found.

There also was no significant difference between the groups in hospitalizations, quality of life and deaths, the authors added.

However, 30 patients with severe vitamin D deficiencies who were taking the supplement did have a significant reduction in exacerbations, the researchers found.

Dr. Diane Gold, a professor of medicine at Harvard Medical School and a professor of environmental health at the Harvard School of Public Health, is the co-author of an accompanying journal editorial. She said that "COPD ranks in the top 10 causes of morbidity and mortality in the United States."

Unfortunately, COPD therapies other than stopping smoking have limited effect in reducing COPD-associated deaths, she said.

This study "does not definitively refute the benefit of vitamin D supplements for reducing COPD exacerbations," Gold said.

"Variability in the underlying disease and genetics are likely to modify the respiratory responses to vitamin D supplementation in people with COPD," she added.

Larger trials with longer follow-up and daily vitamin D dosing are needed to understand the variability in respiratory responses to vitamin D supplementation, Gold said. "And also to assess rarer COPD outcomes such as hospitalization or deaths, or outcomes with longer latency such as changes in lung function, fractures, cardiac outcomes or lung cancer."

Another expert, Dr. Michael Holick, a professor of medicine, physiology and biophysics at Boston University School of Medicine, said he is not surprised some patients benefited from vitamin D.

"There is evidence that vitamin D deficiency exacerbates asthma and lung function," he said.

"We know vitamin D has an impact on reducing inflammatory activity and fighting infections, all of which are chronic problems in patients with COPD," Holick said.

More information

For more information on COPD, visit the U.S. National Library of Medicine.