Coming on the heels of two studies discounting the usefulness of vitamin B, folic acid, vitamin D and calcium supplements for cancer prevention, U.S. researchers report that vitamins C and E supplements won't help prevent cancer, either.

The same team also recently reported that vitamin C and E supplements weren't helpful in protecting users against heart disease.

"At least in the context of two very common outcomes -- cardioprotection and chemoprevention -- we see no compelling evidence to take vitamin E or C supplements," said one of the study's authors, Dr. Howard Sesso, an assistant professor of medicine in the division of preventive medicine at Brigham and Women's Hospital in Boston.

Sesso is expected to present the findings Sunday at an American Academy of Cancer Research (AACR) meeting in Washington, D.C.

The study included almost 15,000 male physicians who were randomly assigned to take a 500 milligram vitamin C supplement daily and 400 international units of vitamin E every other day, or placebo pills for the 10 years of the study. All of the men were over the age of 50 at the start of the trial.

The participants experienced a total of 1,929 cases of cancer, including 1,013 prostate cancers. Overall, 490 men taking vitamin E developed prostate cancer compared to 523 in the placebo group, a difference that Sesso said was not statistically significant. Similar results were seen for vitamin C. The overall risk of cancer generally was also not statistically significant between the two groups.

"This is a very large, long-term clinical trial, and it was determined there was no effect from E or C," Sesso concluded.

Another expert wasn't surprised by the findings.

"This is preliminary data, but it is pretty consistent with what we're seeing in other research with individual nutrients. When you take the nutrient out of its natural environment, it may not be protective," said Jennifer Crum, a nutritionist at the New York University Cancer Institute, who added that in foods, vitamins and other nutrients likely work together to provide protection against cancer.

"People are starting to realize the importance of the overall picture," said Crum, who recommended that people begin by making small changes, such as exercising a little bit longer or adding another vegetable a day to your diet. "When people make small changes for their health -- exercising for 20 to 30 minutes a day, eating better -- we see lower rates of cancer recurrence," she said.

Sesso also recommended focusing on a healthy diet, rather than individual components. "There are things we know about cancer prevention," he said. Sesso advised people to "eat a well-balanced diet, maintain a healthy weight, don't smoke, and exercise regularly."

In other studies being presented at the AACR meeting, researchers looking at calcium supplementation's effect on colorectal cancer did have some good news. In people who took calcium supplements, but maintained a low calcium-to-magnesium intake ratio, the risk of colorectal cancer was reduced. The study was done by scientists at Vanderbilt University, in Nashville, Tenn., and Dartmouth Medical School in New Lebanon, N.H.

A third study found that taking aspirin could affect blood levels of prostate-specific antigen (PSA), which is used to gauge men's risk for prostate cancer. The research, also from Vanderbilt, suggests that aspirin might, therefore, decrease physicians' ability to detect prostate cancer in men.

The finding echoes another study, published recently in the journal Cancer. However, what isn't clear is if these lower levels indicate a reduced risk of prostate cancer or just a reduced ability to detect the disease based on PSA. Experts advise letting your doctor know if you've taken any pain-relieving medications such as aspirin before having a PSA test.