MONDAY, Dec. 12, 2005 (HealthDay News) -- The more vitamin D you have in your bloodstream, the healthier your lungs may be, a new study suggests.
Low vitamin D levels have already been linked to an increased risk of osteoporosis, high blood pressure, diabetes and cancer. Now, researchers from New Zealand, using data from the United States, have found an association between vitamin D levels and how well the lungs work.
"As far as we are aware, this is the first time that anyone has identified this association between lung function and vitamin D," said Peter Black, lead author of the study, which appears in the December issue of Chest. He is a researcher at the University of Auckland in New Zealand.
Black used data from the U.S. Third National Health and Nutrition Examination Survey (NHANES III), carried out from 1988 to 1994. In the study, he looked at more than 14,000 persons, all aged 20 and above, who were interviewed at mobile exam centers. They had lung function tests performed and had their blood levels of vitamin D measured.
Then Black's team divided the vitamin D results into five groups, or quintiles. The higher the vitamin D levels, the better the results on the two lung function tests, they found. The two tests were the FEV1 (forced expiratory volume; the amount of air blown out in the first second during a maximum exhalation) and FVC (forced vital capacity; the total amount of air blown out during a maximum exhalation).
"The difference between the lowest and highest quintile of vitamin D levels [on the lung function tests] was 4 percent for both FEV1 and for FVC," Black said. "This sounds small, but the changes seen in this study are large compared with most environmental factors that affect lung function."
The association between vitamin D levels and FEV1 test results was greater for those over age 60 and for current or former smokers.
"We don't know what the mechanism is," Black said. "The effect of vitamin D on bones is well recognized, but vitamin D can also influence the growth of other types of cells in the body and the formation of connective tissue by other types of cells in the body. The tissues in the lung undergo a process of renewal and remodeling throughout life, and it is conceivable that vitamin D may influence this, but further work is necessary to find out if this is the case."
Vitamin D is found in foods such as fortified milk, salmon, mackerel, tuna and sardines. There is no recommended dietary allowance (RDA) of vitamin D, although an adequate intake for healthy people is 200 international units (IUs) for adults aged 50 and under, 400 IUs for those aged 51 to 70, and 600 IUs for those aged 71 and older. The body also makes vitamin D after exposure to ultraviolet rays from the sun.
Dr. Norman Edelman, chief medical officer for the American Lung Association, called the new research an interesting observation. "I am surprised about the magnitude of the effect [of vitamin D], which is relatively large," he said.
However, he added a caveat: "You can't really infer a causal relationship. It's an association. It's still not accepted as clinical fact."
Edelman continued, "The other thing I really worry about is people will read these things, and will find what they want to in it." For instance, a smoker may think he just has to take extra vitamin D to undo the damaged caused by cigarettes.
The study doesn't warrant a suggestion to take extra vitamin D, he cautioned.
Black agreed. "I don't think we have enough information based on this study alone to justify that sort of recommendation," he said. "I think the take-away message is that low vitamin D levels are not desirable. This doesn't just relate to lung function. A low vitamin D level is linked to bone disease, and an association has been suggested between low vitamin D levels and other diseases such as diabetes and coronary heart disease. The commonest reason for having a low vitamin D level is avoidance of sun exposure. While excessive sun exposure can cause damage to the skin, it is not desirable to completely avoid sun exposure if one is to maintain normal vitamin D levels."
The study will hopefully trigger other research, Black said. "Lung function declines with age. It would be of interest to see if long-term supplementation with vitamin D modifies this decline in lung function."
More information
To learn more about vitamin D, see U.S. National Institutes of Health Office of Dietary Supplements.
