Vitamin D May Improve Lung Function

NEW YORK (Reuters Health) - People with higher vitamin D levels in their blood may breathe a bit easier than others, a study published Monday suggests.

Using data from a U.S. government health survey, researchers in New Zealand found that adults with the highest vitamin D levels generally showed better lung function than those with the lowest blood levels of the vitamin.

This difference in lung capacity, according to the study authors, was even greater to the difference seen between former smokers and nonsmokers.

That may not be significant for healthy people, but it could be for people with serious respiratory conditions, such as chronic obstructive pulmonary disease (COPD), lead study author Dr. Peter N. Black told Reuters Health.

Black and Dr. Robert Scragg from the University of Auckland report the findings in the December issue of the medical journal Chest.

Vitamin D is known to work in concert with calcium and other nutrients to maintain strong bones, and it's also believed to support a healthy immune system and promote normal cell growth and maturation throughout the body.

Low vitamin D concentrations in the blood have been linked to an elevated risk of diseases, such as high blood pressure, heart disease and certain cancers, although it's not clear that vitamin D levels are a direct contributor to these disorders.

Similarly, the current study cannot establish low vitamin D stores as a cause of poor lung function, according to Black. So it's premature to recommend the vitamin as a way to improve respiratory health, he said.

Still, because the study accounted for other factors in lung function -- including study participants' age, exercise habits and blood levels of certain other nutrients -- it seems likely that vitamin D has some direct benefit, Black noted.

The only way to know for sure, he said, is to conduct a clinical trial in which people are randomly assigned to take either vitamin D or a placebo, and then have their lung function followed over time.

The researchers based their findings on data from a national study of 14,091 Americans age 20 or older. Participants were interviewed about diet and lifestyle habits, underwent lung function tests and had their blood levels of vitamin D and other nutrients measured.

After dividing the men and women into five groups based on their vitamin D levels, the researchers found that those with the highest levels scored significantly better on lung function tests than those with the lowest concentrations of the vitamin.

Black said he could only speculate on why vitamin D levels might affect lung function. Like all body tissue, he explained, lung tissue undergoes repair and "remodeling" throughout life. Since vitamin D influences the growth of a variety of cell types, it may play a role in this lung repair process.

Vitamin D levels in the blood depend partially on sun exposure, since sunlight triggers the synthesis of the vitamin in the skin. It can also be consumed through multivitamins or foods such as fortified milk and cereals, and certain fish, like salmon, tuna and sardines.

SOURCE: Chest, December 2005.