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Vitamin D level linked to better physical function in seniors

Posted May 03 2010 12:00am

One area of particular interest in anti-aging research is the role that diet plays in keeping bones and muscles strong from infancy to old age. For instance, a limited number of studies point to the possibility that optimal intake of vitamin D (the “sunshine” vitamin) might help keep our muscles strong and preserve physical function. Although there are only few longitudinal studies investigating this relationship, their findings have been mixed. To help understand this diet-health association, Dr. Denise Houston from the Sticht Center on Aging at Wake Forest University and her collaborators studied the relationship between vitamin D level and physical function in a group of relatively healthy seniors living in Memphis, TN and Pittsburgh, PA.

This study was part of the Health, Aging, and Body Composition (Health ABC) study initially designed to assess the associations among body composition, long-term health conditions, and mobility in older adults. For Houston’s segment of the investigation, she studied 2788 seniors (mean age:  about 75 years old) for 4 years. At the beginning of the study, they assessed vitamin D status by analyzing each person’s blood for the level of 25-hydroxyvitamin D, a precursor for activated vitamin D. At baseline and then 2 and 4 years later, the research team then determined whether circulating 25-hydroxyvitamin D was related to the participants’ physical function. Specifically, they looked at how quickly each participant could walk a short distance (6 meters) and rise from a chair five times as well as maintain his or her balance in progressively more challenging positions. Each participant was also put through a battery of tests assessing endurance and strength.

When the results were tabulated, seniors with the highest levels of 25-hydroxyvitamin D had better physical function. And, although physical function declined over the course of the study, it remained significantly higher among those with the highest vitamin D levels at the beginning of the study compared to those with the lowest vitamin D levels. The scientists were not surprised to learn that, in general, vitamin D consumption was very low in this group of otherwise healthy seniors. In fact, more than 90 percent of them consumed less vitamin D than currently recommended, and many were relying on dietary supplements.

The good news: a higher circulating 25-hydroxyvitamin D level is related to better physical function in seniors. But it’s impossible to tell from this type of research whether increasing vitamin D intake will actually lead to stronger muscles and preserve physical function. This is partly due to the fact that our bodies can make vitamin D if they get enough sunlight. So, it is possible that the participants with better physical function had higher vitamin D status simply because they were able to go outside more often. Indeed, the ominous “chicken-or-the-egg” question can only be answered by carefully controlled clinical intervention trials. Nonetheless, it is possible that getting more vitamin D from foods (like fortified milk and oily fish) or supplements will help maintain youth and vitality as we enjoy longer lifespans. As Houston points out: “Current dietary recommendations are based primarily on vitamin D’s effects on bone health. 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.”

Paying attention to how much vitamin D we get is likely important at every age and will help enhance the “quality” component of life as we enter our senior years (Adapted from Eurekalert).

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