Vitamin D may decrease risk of breast cancer

A serum 25 hydroxyvitamin D level of 30 ng/mL or higher was associated with at least a 50% lower risk of breast cancer, according to the findings of a meta-analysis of three observational studies.

Together, the findings lend support for annually measuring serum vitamin D levels to better identify women at risk for breast cancer, according to the study’s lead author, professor of family and preventive medicine at the University of California, San Diego.

Yet experts disagree on whether there is enough evidence to recommend any intervention that would inevitably result when a patient is found to have low levels of serum 25 hydroxyvitamin D (25[OH]JD).

The departments of cancer biology and public health sciences at Wake Forest University, Winston-Salem, N.C. said that they don’t care how many observational studies there are. There are a lot of good reasons to be concerned about Vitamin D. Low levels of the vitamin probably are related to a number of outcomes that they care about.

The meta-analysis of data from 2,274 women with breast cancer and 2,268 controls without breast cancer indicated a linear dose-response gradient between serum 25(OH)D levels and the risk of breast cancer.

The higher the level of vitamin D metabolites in the serum, the lower the incidence rate of breast cancer, reported during the annual meeting of the American Association for Cancer Research.

The doctor explained that four recent observational studies showed an inverse association between serum 5 (OH)D and risk of breast cancer, but did not specify the 25(OH)D serum levels of reduction in breast cancer incidence. The studies for his meta-analysis were chosen because they provided data on risk of breast cancer according to quintile of serum 25(OH)D.

In the first study included in the analysis, researchers recruited 179 breast cancer patients and 179 controls and found that women with low levels of serum 25(OH)D and a polymorphism in the vitamin D receptor gene were 6.25 times more likely to have breast cancer, compared with women who had higher levels and no genetic polymorphism.

In the second study, blood samples were taken from 701 cases and 724 controls, women in the highest quintile of 25(OH)D had a relative risk of 0.73 for having breast cancer, compared with those in the lowest quintile.

In the third study, serum 25(OH)D levels were compared between 1,394 cases and 1,365 controls. Again, the researchers found that the serum 25(OH)D concentrations were significantly inversely associated with post-menopausal breast cancer risk. The strongest inverse association was seen in women with levels below 50 nmol/L (20 mg/mL).

When the data were combined, a sigmoid dose-response gradient was observed between serum 25(OH)D and risk of breast cancer and was consistent across all studies, colleagues concluded that more cohort studies would be worthwhile but, in the meantime, public health action to raise serum 25(OH)D to 30 ng/mL or more should be started.

He commented that the pooled data from these trials add to the evidence for a link between low serum vitamin D and breast cancer, a link that he and his colleague, also of California, San Diego, have long proposed.

They are confident that they can prevent half the breast cancer in women in the United States, if they could raise serum vitamin D levels to 32 ng/mL.

They are trying to get doctors, public health officials, and the women themselves involved, and they urge women to get their vitamin D tested. It’s as important, he would say even more important than mammography.

Women whose serum 25(OH)D levels fall below 32 ng/mL should take supplements until they reach that level. This would be the best thing they could do for the prevention of breast cancer.

How much vitamin D women should take depends on where they live and their routine sun exposure. If they live in New York, they need a minimum of 2,000 IU/day. If they’re in San Diego, they could get away with 1,000. Women in intermediate latitudes could take intermediate amounts.

The doctor cited what he called a “landmark” study that supports his assertion that vitamin D reduces breast cancer risk. That study, funded by the National Institutes of Health, showed that women who took 1.100 IU/day of vitamin D3 for 4 years three times more than is currently recommended by the US Recommended Daily Amount (RDA) lowered their risk of cancer by more than 60% compared with women who took placebo.

Professor of medicine at the University of Califor nia, Los Angeles, countered, however, that it is too soon to claim that upping the intake of vitamin D can ward off breast cancer.

In 2006, it was reported that a Women’s Health Initiative trial found no reduced breast cancer risk in 18,000 women randomized to 1,000 mg of calcium carbonate and 400 IU/day of vitamin D when compared with 18,000 women given a matching placebo.

The results from a doctor’s meta-analysis “require a much more cautious interpretation.”

This is a selective meta-analysis. It’s not comprehensive, and there are negative studies that were not included. At best, review shows an association, but it does not establish casualty. Before public health policies are changed, the lessons of combined hormone therapy and purported heart disease benefit should be remembered.