Vitamin D and cancer – a lot of hyperbole – but caution is needed
(July 2007)

An article in the American Journal of Clinical Nutrition in June 2007 received a huge amount of publicity trumpeting vitamin D and calcium supplements as cancer preventives. The study, conducted in Nebraska, enrolled 1,179 community-dwelling women over age 55. They were divided into three groups: one received 1,100 International Units of vitamin D daily (higher than the standard supplement dose) and 1,500 milligrams of calcium; a second was given calcium alone; and the third was given an inactive placebo and served as the controls. At baseline, average blood vitamin D levels were in the normal range. The vitamin D-calcium group had a 77 percent reduced risk of cancer over a four-year period. Calcium alone did not show a statistically significant reduction in cancer occurrence.

This study sounds impressive and will encourage women (and men, too) to take potentially toxic amounts of vitamin D supplements. But, in actuality, this study should not prompt anyone to take large amounts of vitamin D supplements.

There are two reasons for our caution.

First, the total number of cancers found in years two to four of the study in all three groups combined was 37. That is too small a number to draw any firm conclusions. In the placebo group, which had the most cancers (18), the numbers of each specific type of cancer were less than five, except for breast cancer (seven cases). You just cannot make any clear judgement with such small numbers.

Second, the only potentially confounding variables taken into account were age and weight (body mass index). There was no attempt to adjust for physical activity, diet, frequency of screening for bowel and breast cancers, or smoking. If the groups differed in regard to any of those variables, such differences could account for the results rather than the vitamin D-calcium supplements.

Thus, this is an interesting, but inconclusive study. More and much larger studies are needed that explore the effects of different doses of vitamin D, the effects on occurrence of various specific types of cancer and allow a determination about whether any benefit found is primarily for those with low vitamin D blood levels. At present, the evidence suggests (not yet adequately proved) that a good vitamin D intake (600 to 1,000 International Units from diet or diet plus supplement or diet plus modest sun exposure) plus a good calcium intake (1,500 milligrams a day from diet or diet plus supplements) will reduce somewhat the risk of bowel cancer. The evidence in other cancers is not adequate.

Every adult should get adequate vitamin D and calcium intake to develop and maintain strong bones. There may be an added benefit in preventing certain cancers (vitamin D 600 to 1,000 International Units for those over 50 years of age; calcium 1,200 milligrams daily for men, 1,500 milligrams a day for women. Remember 20 minutes of sun exposure to uncovered arms three times a week will result in production of substantial amounts of vitamin D. CLICK HERE for (1) tables of foods and beverages with good amounts of vitamin D, (2) high calcium foods and beverages, and (3) high calcium-low fat foods and beverages.

In sum, it is a good idea to get adequate amounts of calcium and vitamin D in your diet; despite the hype no conclusions can be drawn about vitamin D or calcium in cancer prevention from this article.