How much vitamin D do you need?
Medical experts still doing research to find the answer
(HealthDay News) Vitamin D, an essential building block for strong bones, is garnering a reputation for its wide-raging health benefits in youth and adulthood.
In addition to preventing rickets in children and bone softening in adults, studies show that it protects against numerous ailments, from diabetes and depression to heart disease and cancer.
"It's like I've said so many times, the colloquial term is a 'no-brainer,' because there are so many potential benefits and the risks are very, very, very, very small," said Joan M. Lappe, professor of nursing and medicine at Creighton University in Omaha, Neb.
The primary way people get vitamin D is by being exposed to the sun, because the body makes this nutrient when the skin is exposed to sunlight. It's also found in certain foods, like egg yolks, saltwater fish, liver and fortified milk, and it's available in supplement form.
Interest in vitamin D has spiked in the wake of a slew of studies underscoring its many benefits.
In 2007, Lappe and colleagues reported in the American Journal of Clinical Nutrition that postmenopausal women who boosted their vitamin D intake dramatically reduced their risk of cancer.
About the same time, the Canadian Cancer Society recommended that adults living in that country consider taking supplements in the fall and winter. Adults at higher risk of insufficient vitamin D levels should taking vitamin D supplements all year round, it said.
While the American Cancer Society acknowledges a growing body of evidence that vitamin D "may have helpful effects on some types of cancer, including cancers of the colon, prostate, and breast," it maintains that more research is needed to determine the appropriate intake and blood levels for reducing cancer risk.
Indeed, most of the evidence to date on vitamin D's benefits has come from observational studies, in which the investigator observes the outcomes of a population but has no control over whether or not patients receive a particular treatment. Randomized controlled trials, in which patients are randomly assigned to receive a treatment or a "control intervention," are still needed, scientists agree.
In 2008, researchers Wake Forest University presented research at the annual meetings of the American Geriatrics Society and Gerontological Society of America demonstrating an association between lower levels of vitamin D and worse performance on a battery of short physical performance tests and slower walk speeds.
Those who started out with a deficiency and later became vitamin D sufficient "had significant and clinically relevant improvements in the short physical performance battery," said Denise K. Houston, an instructor in internal medicine-gerontology at Wake Forest University Baptist School of Medicine.
More recently, a review in the Journal of the American College of Cardiology linked vitamin D deficiency with increased risk for heart attack and stroke.
Another study found an association between vitamin D insufficiency and greater body mass and shorter stature during puberty.
The Institute of Medicine (IOM) says people need 200 to 600 international units (IU) of vitamin D daily. However, the American Academy of Pediatrics recommends 400 IUs daily for children and teens -- double what IOM suggests for that age group. And many clinicians believe the recommended levels for adults are far too low.
A study using federal data found that 41 percent of men and 53 percent of women in the U.S. have lower-than-recommended blood levels of vitamin D.
According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, just 15 minutes in the sun a few times a week without sunscreen is enough for most to make and store a sufficient amount of vitamin D.
But those who live in northern latitudes may not get adequate sunlight exposure to meet their daily requirement, Lappe noted.
People who are older, homebound, have dark skin or have limited sun exposure also are at higher risk of vitamin D deficiency, according to the Office of Dietary Supplements.
So how much D do adults really need? Some experts recommend roughly 1,000 IUs a day. Lappe takes 2,000 IUs and is thinking about boosting her intake now that winter is here. Studies suggest vitamin D may ward off bacterial and viral infections, she noted, and "that's worth taking a pill every day."
On the Web
For the facts on vitamin D, visit the U.S. government's Office of Dietary Supplements.
Joan Lappe, Ph.D., R.N., professor of medicine and nursing, Criss/Beirne Endowed Chair, School of Nursing, Creighton University, Omaha, Neb.; Denise K. Houston, PhD, RD, instructor, Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, Winston-Salem, N.C.; June 2007, American Journal of Clinical Nutrition ; Dec. 9, 2008, Journal of the American College of Cardiology; July 19, 2007, New England Journal of Medicine ; Canadian Cancer Society, June 8, 2007, news release; Nov. 2008, Pediatrics ; Albert Einstein College of Medicine, Aug. 18, 2008, news release; McGill University, Dec. 10, 2008, news release; American Cancer Society, Atlanta; Office of Dietary Supplements, National Institutes of Health; Bethesda, Md.
Publication date: March 2009
Karen Pallarito H ealthDay Reporter
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