Too Little Vitamin D May Affect Asthma Symptoms
Many experts suggest supplementing amounts from sunshine and food
(HealthDay News) -- Vitamin D may harbor a "double whammy" for asthma sufferers.
Low levels of the vitamin have been linked to worsening asthma symptoms, and too little vitamin D also has been shown to make a common asthma treatment less effective.
One research study found that when vitamin D levels in people with asthma dipped below 30 nanograms per milliliter (ng/mL), the hyper-responsiveness of their airways nearly doubled and levels of inflammatory substances in their blood increased.
That finding suggests that low vitamin D levels are associated with more inflammation, and that increasing vitamin D levels might help treat asthma in those who don't have enough of the so-called "sunshine vitamin."
"There is a potential that restoring normal vitamin D levels in people with asthma may help improve their asthma," the study's lead author, Dr. E. Rand Sutherland, chief of pulmonary and critical care medicine at National Jewish Health in Denver, told HealthDay.
The study, which was published online in the American Journal of Respiratory and Critical Care Medicine, also found that people with low levels of vitamin D were more likely to have a poor response to oral steroid therapy, a common treatment for more severe asthma.
"It may be that vitamin D is acting as a modifier of the immune system or a modifier of steroid response in ways that are relevant to people with asthma," Sutherland said.
Just over 50 people with asthma participated in the study, which involved measuring their lung function, airway responsiveness and response to steroid treatment. Participants also had blood tests to measure their vitamin D levels, as well as markers of inflammation, such as TNF-alpha.
Vitamin D primarily comes from sun exposure, but it's also found in fatty fish and dairy products. The current recommendation for daily intake of vitamin D is between 400 international units (IU) and 600 IU, depending on a person's age.
However, recent research has suggested that low levels of vitamin D may be associated with certain cancers, diabetes and heart disease, among other conditions. Because of this, some experts have suggested that recommended levels of vitamin D should be increased.
A report from the Institute of Medicine, though, says that most Americans are getting sufficient quantities of vitamin D and could actually end up getting too much if they take large vitamin D supplements, along with sun exposure and increasing dietary exposure from vitamin-D fortified foods.
Too much vitamin D, it seems, can also be bad. Excess vitamin D can cause kidney and tissue damage, according to the institute.
Supplements of 400 to 600 international units (IU) are probably safe, Sutherland noted, adding that "there is likely little harm in adhering to those guidelines."
Some experts, however, encourage higher intake. Dr. Michael F. Holick, director of the Vitamin D, Skin and Bone Research Laboratory at Boston University School of Medicine, told HealthDay, "It's pretty clear that you need a minimum of 1,400 and up to 2,000 IU a day, and if you are obese, you probably need at least one and a half to two times as much because the fat sequesters the vitamin D."
On the Web
To learn more about asthma, visit the U.S. Centers for Disease Control and Prevention.
SOURCES: HealthDay News; E. Rand Sutherland, M.D., M.P.H., chief, division of pulmonary and critical care medicine, National Jewish Health, Denver; Michael F. Holick, Ph.D., M.D., professor, medicine, physiology and biophysics, and director, Vitamin D, Skin and Bone Research Laboratory, Boston University School of Medicine, Boston; Jan. 28, 2010, American Journal of Respiratory and Critical Care Medicine, online; Institute of Medicine (www.iom.edu)
Author: Serena Gordon
Publication Date: Jan. 31, 2011
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