In a new study of people with moderate or severe lung disease, taking large amounts of vitamin D was not linked to any symptom relief, researchers from Belgium report.
Prior research suggested that up to three quarters of people with severe chronic obstructive pulmonary disease, or COPD, are deficient in the vitamin. So it was thought that giving them extra vitamin D might help prevent exacerbations in symptoms or trips to the hospital because of shortness of breath or mucus in the airways -- but that turned out not to be the case.
"Supplementation with vitamin D is not going to cure their disease," said Dr. Wim Janssens, one of the study's authors from University Hospitals Leuven.
"It is again clear for COPD patients that these exacerbations are really hard to treat" and prevent, Janssens told Reuters Health.
"There are a lot of relapses. We're basically failing in treating these."
Though vitamin D is most often associated with bone health and osteoporosis, Janssens said the theory has been that the vitamin may help reduce inflammation, including inflammation in the airways that worsens COPD symptoms, such as coughing and trouble breathing.
COPD is irreversible impairment of lung function, including emphysema and chronic bronchitis, often caused by smoking. One large national health survey suggests some 24 million Americans have the condition, according to the Centers for Disease Control and Prevention.
Janssens and his colleagues randomly assigned 182 people at their hospital with moderate to severe forms of the disease to take high-dose vitamin D pills, or a vitamin-free placebo pill, every four weeks for a year. One hundred and fifty of them finished the study.
Over that year, patients on vitamin D reported a total of 229 exacerbations in symptoms, for an average of 2.8 exacerbations in each patient. That was not statistically different from the 239 exacerbations, or 2.9 per patient, among those taking the placebo.
Symptoms were severe enough to send patients taking vitamin D to the hospital 79 times during the study, and people in the placebo group 73 times.
There was also no difference between the two groups in the amount of time until patients had their first exacerbation, or in measures of lung functioning, fatigue or the risk of death.
The researchers did find that among 30 people who had a very severe vitamin D deficiency at the start of the study, those taking the supplements had fewer problems with symptoms.
But because they didn't plan to explore that question from the beginning, and only found it on a second look at the data, it's hard to tell what the finding means.
"That would indicate that if there's any effect, there might be something in patients with really low levels. That's not the majority of patients with COPD," said Dr. Ken Kunisaki, from the Minneapolis VA Healthcare System.
More research would be needed to confirm if the vitamin is of any benefit even in those very deficient patients, added Kunisaki, who has also studied vitamin D in COPD but wasn't involved in the new research.
He said the current findings are in line with other research suggesting that although vitamin D deficiency might be more common in people with COPD, higher levels don't necessarily seem to equate with fewer symptoms.
"Unfortunately the results have been somewhat disappointing," Kunisaki said. "Right now there's no evidence that patients with COPD are going to benefit from additional vitamin D."
Researchers have also proposed that vitamin D may be helpful in patients with multiple sclerosis or tuberculosis, among other diseases, but studies generally haven't panned out, Janssens and his colleagues wrote in their report, published Monday in the Annals of Internal Medicine.
He said that in spite of his team's lack of positive findings, people with or without COPD shouldn't ignore very low vitamin D levels.
"If you're deficient, you need supplementation to normal levels just to treat your bone, to protect from osteoporosis and fractures," he said. "If you (have) severe deficiency, supplementation might also be effective for inflammation" associated with COPD.
Kunisaki cautioned that researchers still don't know whether there are long-term risks associated with taking high doses of vitamin D or other vitamins.