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One of the largest and most thorough studies to date finds that regular use of low-dose aspirin and vitamin E won't help prevent cancer -- at least not in women. Results from the Women's Health Study, published in two papers in this week's Journal of the American Medical Association, provide some of the strongest evidence yet in the ongoing debate about the role of these compounds in cancer prevention.

The study, run by doctors at Harvard Medical School and Brigham and Women's Hospital in Boston, involved nearly 40,000 healthy women 45 and older. Half of them were randomly assigned to take a low dose of aspirin (100 mg) every other day while the rest were given a placebo, or dummy pill. Likewise, half of them were randomly assigned to take 600 IU (international units) of vitamin E every other day, while the rest received a placebo.

Researchers tracked the women for an average of 10 years to determine whether either compound had an effect on cancer (the vitamin E portion also looked at its effect on heart disease).

They found no differences in overall cancer rates or cancer deaths between women who did or did not take aspirin or between women who did or did not take vitamin E.

The researchers also looked at rates of specific types of cancer, including breast, colon, and lung. Taking vitamin E did not have any effect on any type of cancer. Taking aspirin also did not have any effect on breast or colon cancer. Results for lung cancer were less clear; aspirin seemed to give women some protection from getting lung cancer, but the finding wasn't statistically significant. Aspirin also seemed to protect women from dying from lung cancer, but the researchers said this finding might be due to chance.

American Cancer Society experts Eric Jacobs, PhD, and Michael Thun, MD, say the findings are important because the Women's Health Study (WHS) was large, long-term, and carefully designed. They wrote an editorial that was published along with the study.

Many previous studies on aspirin and vitamin E have involved fewer people, and many of them only followed participants for a few years -- perhaps not long enough to be able to find any effect from either compound. Furthermore, randomized controlled trials like the WHS are considered the gold standard in medical research and provide the most reliable results. That's because they directly compare treatments and outcomes and can better account for other factors that may influence a person's cancer risk than other types of studies. When it comes to vitamin E, these strengths add weight to the results of several previous studies that also showed no cancer benefit.

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"Although ongoing randomized trials will eventually provide further information, the promise of [vitamin E] as a cancer prevention agent appears to be dimming," they wrote.

But the same isn't necessarily true for aspirin. Even though the WHS design was strong, Jacobs and Thun say it's too early to close the book on aspirin as a potential cancer-fighter.

"We should not be discouraged by these [negative] results," Thun said.

It may be that people need to take aspirin every day -- not just every other day -- in order to see some sort of cancer prevention, he and Jacobs note. Or perhaps higher doses are required. Aspirin may also have an effect on specific cancers that weren't seen in the Women's Health Study.

Indeed, in a separate study published in the Journal of the National Cancer Institute, Thun, Jacobs, and other ACS colleagues report that aspirin may protect men from prostate cancer.

They looked at more than 70,000 men who were taking part in an ACS study about lifestyle and disease. The men reported how often they took aspirin or similar painkillers (known as NSAIDs, or nonsteriodal anti-inflammatory drugs) over the course of about 7 years.

Men who took aspirin or another NSAID regularly (about 30 pills per month) for 5 years or more had an 18% lower risk of developing prostate cancer than men who did not use these drugs.

The study supports the findings of previous research that also suggested aspirin and similar drugs might help protect against prostate cancer, said lead author Jacobs. But the new findings aren't conclusive.

The study couldn't completely control for other factors that may have influenced a man's prostate cancer risk. And because the study relied on men's memory of their aspirin use, it's possible that some participants misreported how often they took aspirin.

Jacobs and Thun say more research is needed to really understand whether aspirin has a role in preventing cancer. Until that question is answered, though, people should not take aspirin in the hopes it will keep them from getting the disease.

"The American Cancer Society does not currently recommend using aspirin or other NSAIDs to prevent cancer," Jacobs said, "because NSAIDs can cause side effects, including serious gastrointestinal bleeding."

But there are steps people can take to lower their risk of cancer, the two researchers point out.

"For example," said Thun, "the American Cancer Society recommends all Americans 50 and older receive a screening test for colorectal cancer, but many Americans do not receive these potentially lifesaving tests."

Another important step: quitting smoking. Cigarette smoking accounts for about 30% of all cancer deaths, and about 87% of deaths from lung cancer, the leading cancer killer in the US.

"Reducing tobacco use is essential for cancer prevention," said Thun.

Citations:
"Low-Dose Aspirin in the Primary Prevention of Cancer: The Women's Health Study: A Randomized Controlled Trial." Published in the Journal of the American Medical Association (Vol. 294, No. 1: 47-55). First author: Nancy R. Cook, ScD, of Brigham and Women's Hospital and Harvard Medical School.

"Vitamin E in the Primary Prevention of Cardiovascular Disease and Cancer: The Women's Health Study: A Randomized Controlled Trial." Published in the Journal of the American Medical Association (Vol. 294, No. 1: 56-65). First author: I-Min Lee, ScD, of Brigham and Women's Hospital.

"Low-Dose Aspirin and Vitamin E: Challenges and Opportunities in Cancer Prevention." Published in the Journal of the American Medical Association (Vol. 294, No. 1: 105-106). First author: Eric J. Jacobs, PhD, of the American Cancer Society.

"A Large Cohort Study of Aspirin and Other Nonsteroidal Anti-inflammatory Drugs and Prostate Cancer Incidence." Published in the Journal of the National Cancer Institute (Vol. 97, No. 13: 975-980). First author: Eric J. Jacobs, PhD, of the American Cancer Society.