Elderly with a high percentage
of body fat have lower levels
of Vitamin D storage
(click to enlarge)
Susan Harris, an epidemiologist at the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts University
and co-author Dr. Bess Dawson-Hughes interviewed 381 obese Caucasian men and women ages 65 and over. The subjects were asked about their sun exposure over a three-month period. Questions included how much time was spent in the sun and how much skin was exposed. They were also asked whether or not they wore sunscreen. Where the person being interviewed lived was also taken into account, because of the variables in weather conditions.
Researchers measured participants' percent of body fat using a dual-energy X-ray absorptiometry (DXA), a precise method for determining body composition. They were grouped into quartiles of percent body fat -- less than 28%, 28 to 33%, 34 to 40% and greater than 40%. Blood levels of 25-hydroxyvitamin D were measured and participants were asked to fill out a dietary questionnaire to measure the amount of vitamin D they obtained from food.
Harris and Dawson-Hughes found that when adjusted for sex, age, seasonality and dietary vitamin D intake, 25-hydroxyvitamin D significantly decreased as body fat increased, (P<0.024). When the researchers further adjusted for sunlight exposure variables, 25-hydroxyvitamin D values still significantly decreased as body fat increased. "Sunlight exposure could not account for low vitamin D stores in older people with high percent body fat," concludes Harris.
Vitamin D is called the "sunshine vitamin" because it is produced by the body when the skin is exposed to ultraviolet (UV) rays from the sun. Vitamin D can also be obtained from foods such as fish and fortified milk and from supplements. When this fat-soluble vitamin enters the body it is converted in the liver to 25-hydroxyvitamin D. This is one of several important forms of vitamin D, and is the form that researchers and clinicians use as an indicator of vitamin D status in individuals.
Vitamin D is especially important because it helps maintain bone health, which is obviously very crucial in the elderly. Harris believes that the most likely explanation seems to be that vitamin D is sequestered in fat tissue, reducing its entry into the blood.
