Vitamin D May Cut Cancer Risk, Study Says

Vitamin D May Cut Cancer Risk, Study Says

 From Cathy Wong,
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Boosting your vitamin D intake with supplements may reduce your risk of breast and other cancers, a new study has found.

The four-year study, published in the American Journal of Clinical Nutrition by Joan Lappe, Ph.D., and colleagues from Creighton University, followed 1,179 women from rural eastern Nebraska with an average age of 67.

The women were divided into three groups: 446 took 1,400 to 1,500 milligrams (mg) of supplementary calcium per day plus 1,100 international units (IU) of vitamin D per day, a similar number took the same amount of supplementary calcium alone, and 288 took placebo pills everyday.

After four years, the cancer risk decreased by 60 percent in those taking both calcium and vitamin D, and by 47 percent in those taking calcium alone.

 

When the researchers excluded cancers that occurred in the first year of the study (assuming that those cancers likely already existed at the start of the study), those taking calcium and vitamin D had an even greater reduction in cancer risk –- 77 percent compared to the placebo (fake) group.

People taking calcium only had essentially an unchanged reduction of risk, which suggests that calcium alone did little for cancer risk.

This is considered one of the most rigorous studies yet on vitamin D and cancer prevention because researchers increased blood levels of vitamin D in some of the study participants, followed them from start to finish, and then compared them to an identical group who received a dummy pill instead of vitamin D.

Research into the link between vitamin D and cancer prevention dates back decades to observations that cancer rates were lower among people living in southern latitudes compared to similar groups in northern latitudes.

The study had a few drawbacks. It was originally designed to monitor the effect of calcium and vitamin D supplements on bone health, and the number of people with cancer in the study was only 50. Also, the study participants were all women, so we don’t know whether the same effect would occur in men.

How might it work? Vitamin D appears to interfere with the action of a hormone called insulin-like growth factor (IGF). IGF has been found to stimulate cancer cell growth by causing them to divide.

Vitamin D is found naturally in oily fish, such as salmon and sardines, and in fortified foods such as milk and some cereals. Sunshine is another source.

Although the American Cancer Society has not made a recommendation to boost vitamin D intake based on the study, the Canadian Cancer Society released new recommendations that, in consultation with a health-care provider, adults in Canada take 1,000 IU of vitamin D supplements a day in the fall and winter. They recommend that those with a higher risk of vitamin D deficiency take 1,000 IU of vitamin D supplements year-round. They made no recommendations for children.

People who spend little time outdoors, wear clothing that covers most of their skin, live in northern latitudes, and those with darker skin are among those at greater risk of vitamin D deficiency.

There are no recommended daily allowances (RDAs) for vitamin D because there is not enough evidence. The United States Institute of Medicine, however, considers 200 IU of vitamin D adequate for children and adults up to 50, 400 IU adequate for adults 51 to 70, and 600 IU adequate for people 71 and over.

Discuss vitamin D intake with your health-care provider. Some other tips:

  • The Institute of Medicine considers 2,000 IU of vitamin D “upper tolerable” limit for adults. For babies up to one year, the upper tolerable limit is 1,000 IU. More than that is potentially dangerous and can affect liver function.
  • Although most multivitamins contain a form of vitamin D called D2 or ergocalciferol, the form used in this study, D3 or cholecalciferol is considered more active.

Sources:

Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP. Vitamin D and Calcium Supplementation Reduces Cancer Risk: Results of a Randomized Trial. American Journal of Clinical Nutrition. (2007) 85.6 1586-1591.

National Institute of Health Office of Dietary Supplements: "Dietary Supplement Fact Sheet: Vitamin D." 2004 National Institute of Health Office of Dietary Supplements June 11, 2007 <http://dietary-supplements.info.nih.gov/factsheets/vitamind.asp>.

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