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.
