Beta-Carotene Can Cut Risk of Prostate Cancer
Nov. 22, 1999 (New York) -- Men with low levels of beta-carotene in their
blood can reduce their risk of prostate cancer by as much as 32% by taking
beta-carotene supplements every other day, report Boston researchers in the
Nov. 1 issue of the journal Cancer. Men with the lowest blood levels of
beta-carotene at the start of the study had the greatest reduction in risk.
Beta-carotene is converted into vitamin A by the body. In addition to its
supplement form, beta-carotene can also be found in many fruits and vegetables
such as carrots, squash, yams, peaches, apricots, spinach, collard or mustard
greens, and broccoli.
Support for beta-carotene as an anticancer agent has been uneven, with at
least two large studies showing an increase in lung cancer in people that
received beta-carotene supplements. However, another study from the Boston
researchers reporting the new data found no harm, but no significant benefit
either. Other studies, notably the Chinese Cancer Prevention Trial, found a
reduced incidence of stomach cancer and mortality in a poorly nourished
population given a combination of beta-carotene, vitamin E, and selenium.
The latest data from the Physicians' Health Study, reported by Nancy R.
Cook, ScD of Brigham and Women's Hospital and Harvard Medical School, support
the hypothesis that beta-carotene may protect against prostate cancer
occurrence in some men. In the study, almost 15,000 male physicians
participated in the study, which was a large study of male physicians that
began in 1982. The men received either beta-carotene or a placebo.
Over the 12 years of study, close to 1,500 men were diagnosed with cancer,
including 631 with prostate cancer. Blood samples from these men were compared
with those of over 2,000 men who did not take beta-carotene supplements. Men
with the lowest blood levels of beta-carotene at the start of the study who
took supplements had a 32% reduction in risk of prostate cancer. Beta-carotene
supplements did not affect the risk of prostate cancer in men who had higher
blood levels of beta-carotene at the beginning of the study.
Like other antioxidants, beta-carotene may prevent cancer-causing substances
from damaging genetic material in cells. While this may be one explanation for
its beneficial effect, Cook and colleagues write, the differing results of the
various studies point to a need for more research with longer follow-up of
patients receiving beta-carotene supplementation.
In an accompanying editorial, an Ohio researcher says the new study provides
a foundation for further research into the role of various factors, including
dietary antioxidants and family history, that converge to increase an
individual's risk of cancer.
"What is clear is that no single study population or approach is
adequate to provide a complete picture of the complex interactions between
dietary antioxidants in foods," writes Steven K. Clinton, MD, PhD, of The
Ohio State University in Columbus.
Clinton says physicians should exercise caution when advising patients about
beta-carotene supplementation for cancer prevention, making certain to
emphasize the importance of healthy dietary and lifestyle patterns coupled with
effective detection. Tests used to detect prostate cancer include the rectal
exam and the prostate-specific antigen (PSA) blood test. The American Cancer
Society estimates that in 1999, nearly 180,000 men will be diagnosed with
prostate cancer, and 37,000 will die.