A 12-year of study involving nearly 40,000 U.S. women has found that regular, low doses of aspirin do not generally prevent cancer, and vitamin E is ineffective in warding off heart disease and cancer.

The report did find aspirin might have a protective effect against lung cancer, but the authors said that needs to be confirmed with more research, and they pointed out that there is no way of knowing whether higher doses of aspirin might have yielded different results.

"However, based on the data currently available, we do not suggest that doctors recommend low-dose aspirin therapy for primary prevention of cancer," said Nancy Cook of Brigham and Women's Hospital in Boston, chief author of the aspirin study.

While aspirin may not work for cancer, a number of earlier studies have found it does appear to help prevent heart disease, a bigger killer of women than cancer.

Tuesday's findings on aspirin and vitamin E were published in two reports in this week's Journal of the American Medical Association. Both were based on data from the Women's Health Study, described as the largest undertaking of its kind involving the two substances.

There were 39,876 healthy women in the study who were at least 45 years of age when it began 1992. They were followed until 2004.

They were divided into four groups. Some got aspirin and an inert vitamin E placebo; others an aspirin placebo and real vitamin E; others both both aspirin and vitamin E and the last group got only placebos for both substances. The dose levels were 100 milligrams of aspirin and 600 international units of vitamin E, every other day.

While the aspirin-cancer findings were negative, earlier data from the same study group released in March found that the aspirin therapy reduced the risk of stroke by 17 percent, and in women 65 and older it did reduce the risk of heart disease, heart attack and stroke.

Eric Jacobs and Michael Thun of the American Cancer Society, commenting on the aspirin-cancer results in an editorial in the same journal, said finding a drug to prevent cancer is inherently difficult.

"It is unrealistic to expect the discovery of an agent that will produce substantial reductions in overall cancer rates in the immediate future," they added.

I-Min Lee, also of Brigham and Women's Hospital and chief author of the vitamin E report, said its findings "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."

The vitamin E study did find a significant reduction in cardiovascular deaths among all the women taking the vitamin, and that women 65 and older taking vitamin E had a lower risk of heart attack, though not stroke.

"These intriguing findings deserve further study," Lee said. "But they were not part of the primary aim of the study ... additionally, previous studies of vitamin E in patients with heart disease have not shown any benefit for cardiovascular deaths. At present, we cannot recommend vitamin E for prevention against cardiovascular disease or cancer,"

Elizabeth Nabel, director of the National Heart, Lung and Blood Institute, which helped fund the study, said "We can now say that despite their initial promise, vitamin E supplements do not prevent heart attack and stroke. Instead, women should focus on well proven means of heart disease prevention."