Older Adults With Higher Vitamin D Levels Have Improved Mobility, Study Finds
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Reviewed By Laura J. Martin, MD
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April 26, 2010 (Anaheim, Calif.) -- Vitamin D, already considered a way to help fight colds, cancer, diabetes, heart disease, and other ills, may also keep people mobile in their golden years, according to a new study.
Older adults who had higher blood levels of vitamin D had better physical functioning, says Denise Houston, PhD, RD, assistant professor of internal medicine at Wake Forest University in Winston-Salem, N.C. She presented the findings Sunday at the Experimental Biology 2010 meeting.
"Those with better vitamin D levels started out better and ended up better on physical performance tests," she tells WebMD.
Vitamin D in Older Adults: Study Details
Results have been mixed in previous studies looking at whether vitamin D helps physical functioning in older adults, Houston says. Some studies found no effect of boosting low vitamin D levels in seniors and other studies showed an association.
Vitamin D, important for promoting calcium absorption, maintaining muscle strength, promoting bone growth and repair, and other activities, is produced when ultraviolet rays from the sun strike the skin and spark its synthesis.
It's found naturally in few foods and is added to others. Deficiency is common, especially with age, because the ability to synthesize vitamin D declines. Older adults also have difficulty converting vitamin D to its active hormone form.
In the new study, researchers wanted to see if vitamin D could delay age-related changes in physical functioning.
So Houston and her colleagues evaluated 2,641 older men and women, on average age 75.
The older adults were part of the Health, Aging, and Body Composition (Health ABC) Study that looked at the links between body composition, health conditions, and mobility with age.
For this new analysis, Houston divided the adults into three groups, depending on whether their vitamin D levels as evaluated from blood samples was low, medium, or high.
Those terms were relative, she tells WebMD, as "two-thirds had vitamin D insufficiency."
For the study, low blood levels of vitamin D were under 50 nanomoles per liter (nmol/L), high blood levels were those 75 or higher, and levels of 50-75 were intermediate.
All the adults were tested to assess physical function, including walking 400 meters (about 1/4 mile) as fast as possible, standing from a chair without using the arms, balance tasks, and other tests of their lower extremity strength and functioning.
The tests were given at the start of the study and repeated two and four years later.
Vitamin D Levels and Physical Functioning
"Over time, everybody declined in the tasks, as expected," Houston says.
However, those who started out with higher vitamin D did better on the tests than those whose vitamin D levels were lower at the start. "People who had higher levels started out with better physical functioning and because they started out better, they remained at higher physical functioning," Houston says.
"Those with adequate or optimal vitamin D status [the highest group] had approximately 5% higher physical performance scores and 5% faster walk speed on the 400-meter walk compared to those with insufficient vitamin D status at the 4-year follow up," she says.
Next, Houston wants to focus on whether vitamin D blood levels can predict disability in older adults and whether supplements can ward off disability and mobility problems.
Vitamin D Levels and Mobility: Second View
The study results aren't surprising to Erica T. Goode, MD, MPH, a physician at the California Pacific Medical Center's Health & Healing Center-Clinic in San Francisco, who was attending the meeting.
"I'm sure that this is accurate," she says of the finding that those adults with higher vitamin D levels performed better on the physical functioning tests.
Vitamin D: How Much Is Enough?
Exactly how much vitamin D is enough for older adults (and others, as well) is a matter of ongoing debate.
According to the Institute of Medicine, an adequate intake is 400 international units (IU) for adults 51 to 70 and 600 IU for people older than 70. A level of 2,000 IU is considered the "upper tolerable limit" by the IOM.
But some nutrition scientists have challenged those recommendations, contending that up to 10,000 IU a day of the vitamin is generally safe.
"By all means, try to get at least 1,000 IU," Goode says.
The IOM is reviewing the data and is expected to have an update in May 2010.
Vitamin D is found in such foods as fatty fish (salmon, 794 IU per 3 oz serving), fortified milk (115-124 IU per cup) and cod liver oil (1,360 IU per tablespoon).
SOURCES: Joseph Heitman, MD, PhD, chair, department of molecular genetics and
microbiology, Duke University Medical Center, Durham, N.C.
Byrnes, E. PLoS Pathogens, published online April 22, 2010.
Julie Harris, PhD, MPH, staff epidemiologist, CDC.
Katrina Hedberg, MD, MPH, interim state epidemiologist, Oregon Department of Health Services, Public Health Division, Portland.
Marcia Goldoft, MD, medical epidemiologist, Washington State Department of Health, Shoreline.
Nicola-Marsden-Haug, MPH, epidemiologist, Washington State Department of Health, Shoreline.
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