Study: Vitamins may not protect against cancer
Reported November 11, 2008
Yet another study shows that vitamin supplements may not offer protection from cancer.
Taking calcium and vitamin D didn’t reduce the risk of breast cancer, according to a study of more than 2,000 postmenopausal women published in today’s Journal of the National Cancer Institute.
Doctors performed the study because researchers had observed lower breast cancer rates in women who consumed more calcium and vitamin D, although no one had tested that relationship scientifically. The study was a smaller part of the Women’s Health Initiative the 36,000-patient study that found hormone therapy raises the risk of breast cancer and heart disease.
Researchers randomly assigned women to take either placebos or 1,000 milligrams of calcium and 400 international units of vitamin D daily. Women and their doctors didn’t know which pills they were assigned. After seven years, the rate of invasive breast cancer in the two groups was the same.
In their paper, authors say it’s possible that the women didn’t take the supplements long enough, given that cancer can take decades to develop. Authors note that they also don’t know the effect of taking either calcium or vitamin D alone, because women in the study took them together.
And in an accompanying editorial, researchers Corey Speers and Powel Brown from Baylor College of Medicine in Houston say the supplements may still have some benefit.
They note that 15% 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 say it’s also possible that taking hormone therapy, which increases breast cancer risk, could have reduced the benefit from vitamin D and calcium. In the future, they write, 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.
This study is the latest to question the usefulness of specific supplements:
Vitamins C and E. A study presented Sunday in New Orleans at a meeting of the American Heart Association found they didn’t prevent heart disease in men, and that vitamin E supplements appeared to raise the risk of bleeding strokes.
CARDIAC CARE: Vitamin E doesn’t prevent heart ‘events’
B vitamins. A second study presented during the meeting found that supplements of vitamins B-12 and folic acid also failed to prevent heart disease. Another study published last week in The Journal of the American Medical Association (JAMA) found that folic acid and other B vitamins didn’t prevent breast cancer or cancer in general.
STUDY: Folic acid, B vitamins offer no cancer protection
Vitamin E and selenium. Last month, the National Cancer Institute stopped a trial of 35,000 men after finding that the antioxidants vitamin E and selenium didn’t prevent prostate cancer. But men who took vitamin E alone had a slightly higher cancer risk, while those taking selenium alone had a higher rate of diabetes.
Beta-carotene, vitamins A and E. And last year, a large analysis in JAMA found that the risk of premature death increased 7% for people who take beta-carotene, 16% for those who take vitamin A and 4% for vitamin E.
In an article earlier this month in the Journal of Clinical Oncology, researchers acknowledged that they have been surprised by some of these negative results. But the authors, who include Gary Goodman of Seattle’s Fred Hutchinson Cancer Research Center, note that humans evolved on a diet with a relatively narrow range of vitamins. It may have been “naive,” they write, to assume that boosting those levels with supplements would prevent disease without causing new problems.
The recent series of negative results, they say, is the result of scientists carefully testing these assumptions.
