Saturday, March 5, 2011

Getting more bang from your vitamin D buck

Vitamin D has emerged in recent years as a “star” nutrient” based on numerous scientific discoveries about its role in human health. For years, vitamin D was most closely associated with calcium metabolism, since the activated form of vitamin D is required to promote calcium uptake into the body. But a few years ago, studies found that vitamin D was far more than just  a fat-soluble vitamin involved in calcium metabolism. It turns out that vitamin D is converted in the body into a hormone, and that the body contains hundreds of cellular receptors for the active or hormonal form of D. As such, hormonal D is involved in hundreds of vital body functions, ranging from effects in the brain to prevention of cancer, diabetes, and cardiovascular disease. Based on these findings, the research on D has exploded. Among the more interesting findings in this regard was a study that found that D is required to activate immune cells known as T-cells. Without D, these important cells simply won’t work. When that happens, you increase the risk of acquiring everything from cancer to upper respiratory infections, such as colds and flu. In fact, several studies have found that those who have optimal intakes of D are far less prone to infection from the influenza virus.

One unique aspect of vitamin D that many people know about is that your body can synthesize vitamin D in the skin after exposure to ultraviolet light. This is a complex reaction involving converting cholesterol compounds in the skin into vitamin D. You need to expose most of your skin surface to the sun for at least 20 minutes, and the sun ultraviolet rays have to be at a certain range in intensity to promote the reaction. In practical terms, this means that standing in the sun while in the nude for three hours during the winter in Boston will give you a frightful case of frostbite, but no vitamin D. The other option is to obtain D from food sources, but such sources are scarce. This is particularly true since it’s now known that you need far more D than was previously believed for optimal health and preventive effects. Exposing yourself to sunlight for 20 minutes will produce about 10,000 units of D in your body. This contrasts with the usual old recommendation to ingest about 800 units of D daily. The truth is that the optimal oral dose of D ranges from 2,000 to 5,000 units a day. How much you need depends on various factors, including age( older people need more),amount of sun exposure, and body fat level. In those with higher body fat levels, D is sequestered in fat tissues, and is less available, thus increasing the requirement for those with excess body fat levels.

An important, but often overlooked aspect, of vitamin d supplementation is that it’s a fat-soluble nutrient. This means that for optimal absorption, you need to ingest it with a meal containing fat. Taking  a D pill with a glass of water doesn’t cut it in this regard. The importance of timing of D intake was illustrated in a new study. The new study involved 13 women and 4 men, who were provided with doses of D ranging from 1,000 to 50,000 units daily. These subjects were told to ingest their D with the largest meal of the day, ostensibly because this meal would likely contain the highest fat content. D levels  were then monitored for 2 to 3 months. Ingesting the D with the largest meal led to a 56.7% increase in the level of active D in the blood, which would have significant health benefits. As such, when you take your D supplement, make sure you ingest it with a meal that contains the highest fat level of the day to promote optimal D uptake in the body.

Mulligan, G, et al. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D.J Bone Min Res 2010;25:928-30.

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