Nearly 10 years of testing on thousands of doctors show two hugely popular vitamins don't prevent cancer. In the latest antioxidant letdown, researchers who followed nearly 15,000 male physicians found no evidence vitamin E or vitamin C supplements protect against cancer.
"We're kind of rocking the foundation of what we were always brought to believe," Ottawa Hospital urologist John Mahoney said after learning the results.We all think that we should be taking vitamins because it makes us more healthy, and yet we can't prove that."
The new research involves preliminary findings from the U.S. Physicians' Health Study II. Researchers tracked 14,641 doctors, aged 50 and older. Each was given either 400 IU (international units) of vitamin E every other day, 500 milligrams of vitamin C daily, or placebos.
After an average eight years of treatment and followup, about 2,000 men had been diagnosed with cancer, including about half with prostate cancer.Neither vitamin E nor vitamin C supplements reduced the risk of prostate cancer, "total cancer" or other cancers such as colorectal or lung.
There were 490 cases of prostate cancer in men who took vitamin E, versus 523 in the placebo group. For total cancer, there were 978 cases in men randomized to vitamin E, compared to 951 who got placebo. It was a similar story for vitamin C: 964 cancers in the vitamin C group, versus 965 in placebo.
Millions of Canadians an estimated 10 to 15 per cent of adults -- take the supplements, even though evidence of any clear benefit for cancer prevention has been "shaky at best," says Howard Sesso, an assistant professor of medicine at Brigham and Women's Hospital in Boston.
"Until you do these much larger-scale, randomized clinical trials, you don't really know what the actual answer is."Based on their trial, as well as others, "we feel that there are no compelling reasons for people to take either vitamin E or C for the prevention of cancer at this time," Sesso says.
The findings will be presented Monday at a meeting of the American Association for Cancer Research in Washington, D.C. Sesso says the results held after they took age, smoking status, personal history of cancer and other factors into account.
Last week, the same team found vitamin E and C supplements had no effect on the risk of heart attacks, stroke, cardiovascular death, congestive heart failure, angina or heart bypass surgery in the same group of middle-aged and older doctors.
They did find an increase in hemorrhagic stroke with vitamin E use. Last month, 35,000 men from the U.S., Puerto Rico and Canada enrolled in a study testing whether 400 IU daily of vitamin E daily, or 200 micrograms of selenium, can prevent prostate cancer.
They were told to stop taking their supplements after a data and safety committee found vitamin E may slightly increase the chance of getting prostate cancer, and that selenium may increase the chance of getting diabetes. The findings aren't proven.
The doctor's study involved men exclusively, but researchers believe the results could be extrapolated to women as well. A study published three years ago involving nearly 40,000 mostly middle-aged women found those who swallowed 600 IU of vitamin E every other day were no less likely to develop breast, lung, colon or other cancers than women taking a placebo.