Vitamin D

Vitamin D

Vitamin D has long been recognized as necessary for efficient absorption of dietary calcium and has been shown to reduce the risk of bone fractures in the elderly. Recent research is finding other important functions of vitamin D including increased muscle strength, gum health and anti-inflammatory properties.1

Until recently, ways of assessing vitamin D adequacy have been severely limited making it difficult to determine the far-reaching effects of Vitamin D. The latest research has found that the optimum indicator for vitamin D status is serum 25-hydroxy-vitamin D (25OHD) or vitamin D3. Vitamin D 2 once thought to be equipotent to vitamin D3 exhibits substantially lower effective potency.2

Researchers are now asking if the RDA of 400-600 IU per day, set in 1997, is enough? The answer is probably no. Published data indicates that higher daily doses of Vitamin D, in the range of 700 to 800 IU per day, may be more effective in preventing fractures and falls in the elderly.3,4 It is thought that vitamin D may improve muscle strength, thereby reducing fracture risk through fall prevention.

There is very little vitamin D found naturally in food, some are saying that supplementation or aggressive food fortification are necessary. Normally most of our daily vitamin D need is met by vitamin D synthesized in the skin due to sun exposure. However there are limiting factors: age, living at higher latitudes, working indoors, use of sunscreens, skin pigmentation and cultural practices that preclude exposing skin when outdoors.

What should the health care professional do with this recent information?

  • Recommend a daily multivitamin containing 400 IU vitamin D plus an inexpensive vitamin D supplement containing 400 IU vitamin D as a preventive measure.1 (The Tolerable Upper Intake Level, “upper limit,” for vitamin D has been set by the IOM at 2000 IU/day. Taking two multivitamin tablets could give too much of some vitamins.)
  • Assess at-risk patients by evaluating their vitamin D status using serum 25-OHD. Look for values of ~ 80 nmol/L (> 32 ng/mL) which appear, at present, to be adequate.2

References

  1. News bites. Tufts University Health and Nutrition Letter. December 2005;23(10).
  2. Haney RP. Beyond calcium: isoflavones, vitamin D and omega-PUFA hold keys to bone health. Presented at: American Dietetic Association Food and Nutrition Conference and Expo. October 23, 2005;St. Louis, Missouri.
  3. Bischoff-Ferrari HA, Dietrich T, Orav EJ, Dawson-Hughes B. Positive association between 25-hydroxy vitamin D levels and bone mineral density: a population-based study of older and younger adults. American Journal of Medicine. May 1, 2004:116:634-9.
  4. Bischoff-Ferrari HA, Dietrich T, Orav EJ, Hu FB, Zhang Y, Karlson EW, Dawson-Hughes B. Higher 25-hydroxy vitamin D concentrations associated with better lower-extremity function in both active and inactive persons aged >60 y. American Journal of Clinical Nutrition. September 2004;80(3):752-8.