Vitamin D For Dummies
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In our increasingly overweight society, weight management has become an important concern. Substantial information suggests that vitamin D plays a role in fat cell biology and that this may relate to weight loss and weight management.

Fat ties up vitamin D. If an overweight person and a normal-weight person take the same amount of vitamin D, the blood level of vitamin D in the normal-weight person goes higher than in the overweight person. The only way an overweight person can get that vitamin D back is by losing weight.

Several observations are consistent with the idea that vitamin D, as well as calcium, may be important in weight loss or weight maintenance. Unfortunately there are inconsistencies between the studies, and often vitamin D and calcium are given together, which makes it impossible to separate their effects on fat. Among them are the following:

  • Higher calcium intake is associated with lower body weight in people and animals. This lowers the serum level of active vitamin D (calcitriol), which suggests that calcitriol normally promotes fat gain.

  • Fat cells have the enzyme that allows them to make calcitriol from 25-hydroxyvitamin D. This suggests fat cells may be influenced by calcitriol even when the serum level of calcitriol doesn’t change.

  • Blood levels of parathyroid hormone, which rise when vitamin D status falls, are associated with more obesity; however, when this happens, serum calcium can also fall.

  • Contrary to the idea that high calcium suppresses obesity by reducing calcitriol levels, calcitriol suppresses the formation of mature fat cells in cell culture experiments.

  • Confounding the picture somewhat, the vitamin D receptor independently promotes the formation of fat cells. This is why mice lacking the vitamin D receptor have less body fat than normal mice.

  • Increasing vitamin D status from serum 25-hydroxyvitamin D levels of 15 to 30 ng/ml (37.5 to 75 nmol/L) was associated with more effective weight loss in a controlled two-year program.

All of this is very interesting and shows that calcitriol plays a role in how a fat cell works. It still isn't known, however, if there is a reliable benefit to either maintaining weight or losing weight that comes from taking more vitamin D. More research is needed to get that answer.

If you’re planning weight-loss surgery (bariatric surgery), one of the complications is poor absorption of vitamin D and other fat-soluble vitamins. Post-surgical patients must take vitamin supplements to maintain target levels of vitamin D and other nutrients. You want to be sure that your vitamin D blood level is normal so that if the association showing that high vitamin D status helps with weight loss turns out to be true, your weight loss proceeds at a satisfactory rate.

About This Article

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About the book author:

Alan L. Rubin, MD has been a physician in private practice for more than 30 years. He is the author of several bestselling health titles, including Diabetes For Dummies, High Blood Pressure For Dummies, and Thyroid For Dummies.

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