A new study in the online edition of the Journal of the National Cancer Institute adds to the amount of evidence showing that vitamins do not prevent cancer of any kind. Just last week, researchers at the Brigham and Women’s Hospital of Harvard Medical School concluded that taking folic acid and other B vitamins on regular basis doesn’t prevent breast cancer or cancer in general.

In October, the National Cancer Institute halted a trial involving about 35,000 men after finding that vitamin E and selenium didn’t prevent prostate cancer. On contrary, researchers found a higher risk for aggressive prostate cancer in participants taking only vitamin E and a small risk of developing diabetes in subjects taking only selenium.

An earlier study (of a much smaller group) conducted on the effect of selenium supplementation on the recurrence of skin cancers did not demonstrate a reduced rate of recurrence of skin cancers, but did show a reduced occurrence of total cancers.

The new study makes no exception and says that vitamin D supplements, taken at a dose of 400 international units per day, may not help prevent breast cancer in women after menopause.

“The message is that there’s benefit from calcium and vitamin D for fracture risk, but taking those supplements won’t be doing much for breast cancer risk. You wouldn’t expect that you’re doing it to improve breast cancer outcome,” said study author Dr. Rowan T. Chlebowsky, a medical oncologist at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Los Angeles.

The study included 36,282 postmenopausal women involved in the Women’s Health Initiative trial. All were between 50 and 79 years old, with no history of breast cancer. The women were randomly assigned to receive either 1,000 milligrams of calcium plus 400 international units daily of vitamin D, or a placebo for an average of seven years.

At the end of the follow-up period, there were 528 cases of breast cancer in the group taking calcium and vitamin D compared with 546 cases in the placebo group – a difference not considered statistically significant.

“The main findings do not support a causal relationship between calcium and vitamin D supplement use and reduced breast cancer incidence, despite the association observed in some epidemiological studies. Current evidence does not support their use in any dose to reduce breast cancer risk,” Dr. Chlebowsky said.

However, the link between vitamin D and calcium and breast cancer prevention should be studied more as the supplements may still have some benefit, according to researchers Corey Speers and Powel Brown from Baylor College of Medicine in Houston who wrote an accompanying editorial to the study. They note that 15 percent of the women assigned to take placebos actually took calcium and vitamin D pills on their own – a fact that may make it harder to spot any differences between the two groups. They further suggested that researchers may want to test higher doses of supplements or design trials with younger women in the hope of stopping breast cancer in its earliest stages.