Physical function was highest in people with the highest blood levels of 25-hydroxyvitamin D (25(OH)D) – the storage form of the vitamin in the body – while lower levels were associated with poorer physical function, scientists from Wake Forest University told attendees at the Experimental Biology 2010 meeting in Anaheim yesterday.
The study does not prove causality, however. Indeed, since we make vitamin D on exposure to sunlight, it is possible that people with better physical function have higher levels simply because they were able to get outside more often.
If future trials support the hypothesis that higher vitamin D may increase physical function in the elderly then increases in recommended intakes may be needed, said researchers led by Dr Denise Houston.
“Current dietary recommendations are based primarily on vitamin D's effects on bone health,” she explained. “It is possible that higher amounts of vitamin D are needed for the preservation of muscle strength and physical function as well as other health conditions.
“However, clinical trials are needed to definitively determine whether increasing 25-hydroxyvitamin D concentrations through diet or supplements has an effect on these non-traditional outcomes,” added Dr Houston.
Vitamin D is well known to support muscle function, and the science supporting the link is sufficiently robust to have merited a positive opinion from the European Food Safety Authority’s (EFSA) Panel on Dietetic Products, Nutrition and Allergies (NDA).
The Panel concluded that “a cause and effect relationship has been established between the dietary intake of vitamin D and contribution to the normal function of the immune system and healthy inflammatory response, and maintenance of normal muscle function”.
Dr Houston and her co-workers analysed data from 2,788 people with an average age of 75. Blood levels of 25(OH)D were measured at the start of the study, two years later, and then again after four years. These levels were then related to the physical function of the participants, measured by a variety of tests including how quickly they could walk 6 metres, how quickly they could rise from a chair five times, and how well they maintained their balance when asked to adopt a challenging position.
Data showed that people with the highest levels of vitamin D levels had better physical function. On the other hand, of the people with the lowest physical function 90 per cent of them had insufficient or deficient levels of vitamin D, said the researchers.
In addition to the EFSA nod of approval, science continues to emerge to support the muscle-benefits of the vitamin, including a recent study from McGill University in Canada found that insufficient blood levels of vitamin D may be associated with the accumulation of fat in muscle tissue, leading to lower muscle strength.
The findings were said to be the first to show a clear link between vitamin D levels and the accumulation of fat in muscle tissue, and were published in the Journal of Clinical Endocrinology and Metabolism (doi:10.1210/jc.2009-2309).
Dr Houston presented as part of the scientific program of the American Society for Nutrition at the Experimental Biology 2010 meeting in Anaheim. NutraIngredients has not seen the full data.
The researchers were affiliated with Wake Forest University, the University of Georgia, University of Pittsburgh, University of California, San Francisco, University of Tennessee, VU University, Amsterdam, and the National Institute on Aging.