"With a growing older population, we need to identify better ways to reduce the risk of disability," said lead author Denise Houston, from Wake Forest University. "Our study showed a significant relationship between low vitamin D levels in older adults and poorer physical performance." Calls for raising the recommended daily allowance of the vitamin have been growing after reports that higher intakes could protect against osteoporosis and certain cancers. Consumer awareness of these health links is also increasing with some outlets reporting massive boosts in sales. The new study, published in the April issue of the Journal of Gerontology: Medical Sciences, analyzed data from the InCHIANTI study, involving 976 people (average age 74.8) from two towns in the Chianti area of Italy. Participants completed a short physical performance test of their walking speed, ability to stand from a chair and ability to maintain their balance in progressively more challenging positions. Additionally, their handgrip strength was also measured.
The researchers report that low levels of vitamin D were associated with five to 10 percent lower scores of physical performance and grip strength. The researchers cautioned that the research does not show that low vitamin D levels are the cause of the poorer physical performance, but Houston added that vitamin D plays an important role in muscle function, so it is plausible that low levels of the vitamin could result in lower muscle strength and physical performance. "But it's also possible that those with poor physical performance had less exposure to sunlight resulting in low vitamin D levels," she said. Current recommendations call for people from age 50 to 69 to get 400 international units (IUs) of vitamin D per day and for those over age 70 to get 600 IUs. Many researchers, however, suggest that higher amounts may be needed.
"Higher amounts of vitamin D may be needed for the preservation of muscle strength and physical function as well as other conditions such as cancer prevention," explained Houston. "The current recommendations are based primarily on vitamin D's effects on bone health." Calls to increase vitamin D intake have been growing. Indeed, only recently fifteen experts from universities, research institutes, and university hospitals around the world called for international agencies to "reassess as a matter of high priority" dietary recommendations for vitamin D because current advice is outdated and puts the public at risk of deficiency (The American Journal of Clinical Nutrition, Vol. 85, pp. 860-868). A recent review of the science reported that the tolerable upper intake level for oral vitamin D3 should be increased five-fold, from the current tolerable upper intake level (UL) in Europe and the US of 2000 International Units (IU), equivalent to 50 micrograms per day, to 10,000 IU (250 micrograms per day). "Recent findings showing the importance of vitamin D status on multiple health outcomes underscore the need for more research on the effects of low vitamin D levels in elderly populations," she said.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive. The latter is derived from plants and only enters the body via the diet. Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body. Source: Journal of Gerontology: Medical Sciences April 2007
Authors: D. Houston, G. Schwartz, S. Kritchevsky, M. Cesari, L. Ferrucci, D. Maggio, A. Cherubini, M.A. Johnson, B. Bartali