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
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