Vitamin D Update
Chester J. Zelasko, Ph.D. | January 8, 2008

Vitamin D has been in the news recently. While recent research seems to favor the reduction of some nutrients such as vitamin E, some experts are recommending an increase in others. Is more vitamin D necessary? This Newsletter will review the science behind the headlines to allow you to make an informed decision.

Vitamin D
Vitamin D seems to have a straightforward function in the body: to maintain serum calcium and phosphorus levels. The way that vitamin D regulates calcium and phosphorous is by controlling the ability of the small intestine to absorb these nutrients from the foods we eat (1). Vitamin-D deficiency contributes to the loss of bone mineral content. In children, this can result in rickets; in adults, a reduction in calcium content of the bones can lead to osteoporotic bones and a subsequent increase in fractures in the elderly.

The two major forms of vitamin D are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). For most of the world, the greatest source of Vitamin D is vitamin D3, which is manufactured in the body from exposure to the ultraviolet rays of the sun; conversion of D3 to the active form is highly regulated by the body to prevent excessive production. Vitamin D2 is the primary dietary source of vitamin D and is found in oily fish and fortified foods such as milk, yogurt, and cheese. Most vitamin D intake comes from dietary supplements as well as food.

The adequate daily intake established by the Institutes of Medicine in 1997 for children and adults up to 50 years is 200 IU per day, age 51-70 is 400 IU per day, and over 70 is 600 IU per day.

Recent Research
Since the Dietary Reference Intake values were set in 1997, research has established a link between vitamin D deficiency and many chronic illnesses. Until recently, vitamin D was thought to affect only the absorption of minerals. However, in a recent review paper, Dr. Michael Holick reported that recent research shows that most cells in the body have the ability to process vitamin D. This has lead to the hypothesis that lack of vitamin D has a role in common cancers, autoimmune diseases, infectious diseases, and cardiovascular disease (2).

In an article first published in 1980 and reprinted in 2006, Drs. Garland and Garland first demonstrated that the mortality rate of colon cancer was higher as the annual mean solar radiation exposure decreased (3). The amount of solar radiation associated with the increased risk runs roughly through the 42nd parallel, which in the northern hemisphere runs roughly from the southern border of Oregon, through the Pennsylvania-New York border, to the Massachusetts-Connecticut border, crossing the southern tips of Lake Michigan and Lake Erie. Above that line in the northern hemisphere and below it in the southern hemisphere, the angle of the sun is too low in winter to supply sufficient sunlight for our bodies to produce enough vitamin D.

In a separate commentary, Drs. Grant and Gorham review the relationship between sun exposure and common cancers (4). As exposure to sun decreases as we move north from the equator, the rates of cancers such as colon, prostate, and breast cancer increase. This relationship is observed with 18 different diseases including non-Hodgkins lymphoma. They go on to suggest that these observations qualify as cause and effect. When exposure to sun decreases, illness increases, taking into account other factors related to the specific cancers.

Most of the studies were either epidemiological or comparative studies examining differences between control groups and subjects with diseases such as colon cancer. Intervention studies haven’t proven quite as effective. In the Women’s Health Initiative, Dr. Holick points out a 29% decrease in hip fractures in a subset of female subjects who consistently used supplements with 1,000 mg calcium and 400 IU vitamin D. While that’s true, the difference meant that 10 out of every 10,000 women who supplemented with vitamin D fractured their hips versus 14 out of 10,000 for those who took a placebo (5)--not overwhelming results, but Dr. Holick points out that the serum levels of vitamin D did not reach 30 ng/ml, a level that is associated with no progression of chronic illness.

More research must be done before the definitive recommendation can be established by the U.S. Institutes of Medicine. The question is this: should we act today based on current available research or do we wait?

Dr. Holick provides a reasonable solution. The Upper Tolerable Limit for vitamin D is set at 2,000 IU. Therefore, there should no negative effect of raising intake to at least 800 IU per day. Drs. Grant and Gorham also suggest raising intake of vitamin D. Because Dr. Holick was on the committee that set the DRIs in 1997, the fact that he is recommending the increase is significant; he is well aware of the conservative nature of setting recommendations that apply to every person in the United States and Canada.

Bottom Line
In light of the evidence put forth by these researchers, combined with the unlikely event of negative effects, it would seem like a good idea to raise vitamin D intake to 800 IUs per day. Much of the U.S. is far enough north to have limited access to sunlight most of the year, so the increase will have to come from supplementation. In addition, vitamin D production from sunlight is affected by skin color, use of sunscreen, and whether you live in the city or the country--so for most of us a year-round increase in our vitamin D supplement is probably our best bet.

And there’s one more factor to consider: the subjects in the Women’s Health Initiative who benefitted from taking calcium and vitamin D supplements were the ones who took their supplements regularly. Remembering to take your supplements is even more critical than raising the amount you consume. If you’re going to expect positive effects, you must take the supplements every day.

  1. DRI Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Food and Nutrition Board, Institute of Medicine. Pps 250-287. National Academy Press. Washington, D.C.1997.

  2. Holick M. Vitamin D deficiency. N Engl J Med. 2007. 19;357(3):266-81.

  3. Garland CF and Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer? International Journal of Epidemiology 2006;35:217–220.

  4. Grant WB and Gorham ED. Commentary: Time for public health action on vitamin D for cancer risk reduction. International Journal of Epidemiology 2006;35:224–225.

  5. Women’s Health Initiative. Calcium plus Vitamin D Supplementation and the Risk of Fractures. N Engl J Med 2006;354:669-83.
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