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    Jennifer Nelson, M.S., R.D. and Katherine Zeratsky, R.D.

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  • Jan. 8, 2009

    Shedding light on vitamin D

    By Jennifer Nelson, M.S., R.D. and Katherine Zeratsky, R.D.

46 comments posted

It's winter in the Northern hemisphere and for many that means sunshine is in short supply. As a result, your vitamin D levels may be on the decline. Should you be worried? How much vitamin D do you really need? What's the best way to get it? Several studies published in the December 2008 issue of the American Journal of Clinical Nutrition attempt to shed light on these questions.

One of the studies found that vitamin D levels appear lower among Americans today than 15 to 20 years ago. Researchers attributed the decline to the following factors: increasing weight, declining milk consumption, and increasing use of sun protection.

On a brighter note, another study demonstrated that fortifying foods, such as milk, with vitamin D does improve vitamin D status in adults.

A third study looked at vitamin D levels in the winter months. The study showed that people who get less sun in the summer need slightly higher vitamin D supplementation in the winter to maintain recommended levels. Interestingly, the top dose in the study was 600 international units, which is higher than the 400 international units of vitamin D generally found in multivitamins.

So what does this all mean? The data we have seems to tell us that:

  • Although 10-15 minutes of daily sun in non-peak hours can provide adequate vitamin D, people who use sun protection (which should be most of us) need to look for other sources of vitamin D.
  • Fatty fish, egg yolks, and fortified foods are good dietary sources of vitamin D. And toxicity from fortified foods is rare.
  • Vitamin D supplements at currently recommended doses can increase vitamin D levels in the body.

Some questions still remain. What happens if you take more vitamin D than the current recommendation? Is there an upper limit beyond which you are harmed rather than helped?

What are your thoughts? For those of you who don't take a multivitamin or vitamin D supplement, will these studies change your mind? For those of you who take a supplement, how much are you taking? What changes have you noticed as a result?

To your health,

Katherine

46 comments posted

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References
  1. Looker AC, et al. Serum 25-hydroxyvitamin D status of the US population: 1988-1994 compared with 2000-2004. Am J Clin Nutr. 2008 Dec;88(6):1519.
  2. O'Donnell S, et al. Efficacy of food fortification on serum 25-hydroxyvitamin D concentrations: systematic review. Am J Clin Nutr. 2008 Dec;88(6):1528.
  3. Cashman KD, et al. Estimation of the dietary requirement for vitamin D in healthy adults. Am J Clin Nutr 2008 Dec;88(6):1535.

MY00493

Jan. 8, 2009

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