Maintain vitamin D: maintain independence

Friday, June 1, 2012. In an article published online on May 9, 2012 in the Journal of Gerontology: Medical Sciences, researchers at Wake Forest School of Medicine report an association between reduced levels of vitamin D and a greater risk of disability or loss of mobility in older men and women.

For the current investigation, nutrition epidemiologist Denise K. Houston, PhD, RD, of Wake Forest Baptist Medical Center's Department of Geriatrics and Gerontology and her associates utilized data from 2,099 African-American and Caucasian participants enrolled in the National Institute on Aging's Health, Aging, and Body Composition (Health ABC) study. Mobility, as assessed by the ability to walk a specified distance and climb stairs, was evaluated every six months over six years of follow-up. Blood samples obtained at the one year follow-up visit were analyzed for serum 25-hydroxyvitamin D and parathyroid hormone levels.

Levels of serum vitamin D of less than 50 nanomoles per liter (nmol/L) were found in 28.9 percent of the subjects, and levels of 50 to less than 75 nmol/L were measured in 36.1 percent. Those whose levels were between 50 and 75 nmol/L had a 27 percent greater risk of developing a mobility limitation and a 30 percent greater risk of mobility disability than those whose levels were at least 75 nmol/L. Among those whose serum vitamin D levels were lower than 50 nmol/L, the risks were 29 percent and 93 percent greater.

"This is one of the first studies to look at the association of vitamin D and the onset of new mobility limitations or disability in older adults," announced Dr Houston. "We observed about a 30 percent increased risk of mobility limitations for those older adults who had low levels of vitamin D, and almost a two-fold higher risk of mobility disability."

Because vitamin D plays a role in muscle function, Dr Houston suggested that reduced levels could decrease physical strength and performance. Deficient levels of the vitamin, which have been implicated in the development of cardiovascular disease and other conditions, can also indirectly impact physical function. "About one-third of older adults have low vitamin D levels," Dr Houston noted. "It's difficult to get enough vitamin D through diet alone and older adults, who may not spend much time outdoors, may need to take a vitamin D supplement."

While the current dietary recommendation for older individuals is just 800 international units per day, Dr Houston remarked that "Higher amounts of vitamin D may be needed for the preservation of muscle strength and physical function as well as other health conditions. However, clinical trials are needed to determine whether increasing vitamin D levels through diet or supplements has an effect on physical function."

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