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Women's Health Study: Long-awaited findings of low-dose aspirin and vitamin E in preventing disease
Results of largest randomized clinical trial of aspirin on cancer, and vitamin E on cardiovascular disease and cancer, show few benefits
The Women's Health Study (WHS) - the largest randomized clinical trial to investigate the impact of aspirin and vitamin E on the primary prevention of cardiovascular and cancer risk - has helped shape some of clinical medicine's basic understanding of disease prevention and women's health. Now, researchers from Brigham and Women's Hospital (BWH), where the WHS is based, are detailing new, long-awaited results that examine if low-dose aspirin (100 mg. every other day) protects healthy women against cancer, and if vitamin E (600 IU every other day) protects healthy women against cardiovascular disease and cancer.
BWH WHS researchers found in this healthy population that regular, low-dose aspirin had no overall effect in preventing cancer, including breast, colorectal, and other site-specific cancers. However, researchers did find that regular low-dose aspirin therapy could confer some protection against lung cancer but recommend further study to clarify these findings. They also could not rule out benefits of higher doses of aspirin. In addition, researchers identified that regular intake of vitamin E supplements did not help prevent overall cardiovascular disease or cancer and did not affect total mortality. However, vitamin E did reduce cardiovascular mortality and, again, researchers recommend that this finding be explored further.
These landmark results are published in the July 6 issue of the Journal of the American Medical Association.
The WHS is a large, randomized, double-blind, placebo-controlled trial funded by both the National Heart, Lung and Blood Institute and the National Cancer Institute to evaluate the benefits and risks of low-dose aspirin as well as vitamin E supplementation in the primary prevention of cardiovascular disease and cancer. The trial included 39,876 healthy female health professionals 45 years of age and older who were monitored for 10 years for occurrence of cancer and major cardiovascular events including heart attack, stroke, and death from cardiovascular causes. In March 2005, long-awaited WHS results demonstrated regular low-dose aspirin therapy reduced the risk of stroke by 17 percent, but did not decrease heart attacks or cardiovascular deaths among all women. However, in the subgroup of women 65 years and older, aspirin reduced the risks of developing overall cardiovascular disease, ischemic stroke, and heart attack.
According to BWH's Julie E. Buring, principal investigator of the WHS, Nancy R. Cook, the lead investigator of the low-dose aspirin and cancer analyses, and I-Min Lee, the lead investigator of the vitamin E and cardiovascular disease and cancer analyses, these results can help physicians better address disease prevention in women.
Low-dose aspirin and cancer
Observational and basic research has suggested a role for aspirin in the prevention of cancer. According to Cook, "There is a growing body of evidence that supports the protective effects of aspirin and NSAID’s [nonsteroidal anti-inflammatory drugs] in cancer prevention. The WHS directly tested the chemopreventive effects of low-dose aspirin in a randomized trial, finding that low-dose aspirin every other day does not confer any protection versus placebo among women, with the possible exception of a protective effect on lung cancer. We believe that the results for lung cancer need to be confirmed in other trials. However, based on the data currently available, we do not suggest that doctors recommend low-dose aspirin therapy for primary prevention of cancer."
For this component of the WHS, researchers established primary endpoints as any invasive cancer, excluding non-melanoma skin cancer, with incidence of breast, colorectal, and lung cancer as secondary endpoints. Researchers also noted this is the first clinical trial to assess the impact of low-dose aspirin therapy on breast cancer. During follow-up, a total of 2,865 cases of invasive cancer were confirmed. Of these, 1,230 were breast cancer (43 percent), 269 were colorectal cancer (nine percent), and 205 were lung cancer (seven percent), with no statistically significant difference in occurrences between the aspirin and placebo groups except for a trend toward reduction in lung cancer in the active aspirin group.
According to Buring, "It is important to note that these data do not address the possible role of higher doses of aspirin in the chemoprevention of cancer."
Vitamin E and cardiovascular disease and cancer
With regard to vitamin E, to date, very few clinical trials have evaluated its impact on lowering the risk of cardiovascular disease and serving as a cancer prevention therapy among healthy persons, despite promising data from lab and observational studies. In the WHS, BWH researchers found that vitamin E had no overall benefits on cardiovascular disease or cancer. However, it did reduce cardiovascular deaths among all women, as well as overall cardiovascular disease in the subgroup of women ages 65 years and older. These secondary findings need to be explored further.
In addition, a recent analysis of previous trials of vitamin E conducted among patients at high risk or with cardiovascular disease raised the concern that vitamin E might increase total mortality. The WHS showed that vitamin E had no effect on total mortality.
According to I-Min Lee, "Even without solid clinical evidence of benefit, many people across the U.S. routinely use vitamin E to prevent cardiovascular disease. The WHS data do not support recommending vitamin E supplementation for cardiovascular disease or cancer prevention among healthy women. At present, a healthy lifestyle and regular screening for cardiovascular health and cancer are a woman's best choices for disease prevention."
In this component of the trial, the primary endpoints of interest were major cardiovascular events (comprising nonfatal heart attack, nonfatal stroke, or cardiovascular death) and total invasive cancer (except for non-melanoma skin cancer). During follow-up, there were 482 major cardiovascular events in the vitamin E group and 517 in the placebo group, representing a non-significant seven percent reduction. For the individual cardiovascular events, vitamin E had no effect on heart attack or stroke, but decreased cardiovascular deaths by 24 percent. There was an exception among women ages 65 years and older, in which vitamin E decreased major cardiovascular events by 26 percent. Regarding cancer benefits, there were 1,437 cases of cancer for participants assigned to vitamin E versus 1,428 for those assigned to placebo, representing no difference between groups. There also was no difference between groups for the most common cancers in women: breast, lung, and colon cancers. There were 636 deaths among women in the vitamin E group, 615 in the placebo group, representing no difference between the groups.
"These findings from the WHS have provided important information directly from women on the roles of aspirin and vitamin E in preventing cardiovascular disease and cancer in women," said Buring. "The WHS will also be able to provide information on the roles of aspirin and vitamin E in the prevention of other important diseases, such as diabetes, loss of cognitive function, rheumatoid arthritis, and vision disorders such as cataract and age-related macular degeneration."