TUESDAY, Nov. 2, 2004 (HealthDayNews) -- Eating plenty of fruits and vegetables may be good for your heart health, but a new study finds it won't lower your overall risk of developing cancer.
The study belies longstanding recommendations that people increase their consumption of fruits and vegetables to ward off cancer. Experts were quick to point out, however, that the latest research applies to any cancer, adding that such a diet could still prevent specific malignancies, such as tumors of the colon or bladder.
Harvard doctors found a 28 percent reduction in cardiovascular risk among nearly 110,000 health professionals surveyed for lifestyle patterns and medical history who include at least five servings of fruits and vegetables in their daily diets.
However, they found no reduction in cancer rates among those who ate five or more servings of fruits and vegetables.
The results "support the recommendation of consuming five or more servings of fruits and vegetables daily. However, the benefit of increasing intake of fruits and vegetables appear to be due primarily to a lower risk of cardiovascular disease, not cancer," the authors concluded. In cancer prevention, "the protective effect of fruit and vegetable intake may have been overstated."
The results appear in the Nov. 3 issue of the Journal of the National Cancer Institute.
For the study, Dr. Walter C. Willett, of the nutrition department of the Boston Harvard School of Public Health, analyzed data from participants in two large ongoing studies that assess how lifestyles influence health. These are the Nurses' Health Study, started in 1976, and the Health Professionals' Follow-up Study, begun in 1986.
Analyzing the results of regular questionnaires filled out by the participants regarding their eating habits and overall health, Willett and his colleagues found those who ate at least five servings a day of fruit and vegetables had a slightly lower risk for chronic diseases such as hypertension and diabetes, and a significantly lower risk for cardiovascular disease.
The authors suggest that this could be due to increased intake of the multiple nutrients that are found in fruits and vegetables, such as folic acid and potassium. Eating green leafy vegetables was particularly associated with a reduction in cardiovascular risk (11 percent).
However, the authors concluded that despite recommendations from health professionals that five or more servings of fruits and vegetables are helpful for cancer prevention, their study found no reduction in risk for cancer among the study participants with a high intake of fruits and vegetables compared to those who had only one serving of these food groups daily.
The median intake of fruits and vegetables for the study participants was five servings a day, comparing favorably to the average intake in the U.S. population of one serving of fruits and vegetables per day. The authors suggest the higher intake of fruits and vegetables among the study participants reflected the fact that they are health professionals and also are in higher socioeconomic level than the average American.
"These results are not entirely surprising," said Marji McCullough, a nutritional epidemiologist at the American Cancer Society, because the study surveyed the effects of fruit and vegetable consumption on all kinds of cancer, rather than just the ones that have shown some risk reduction from dietary habits.
"I still think there are reasons to believe that fruits and vegetables might impact specific cancers, like colorectal and bladder cancers," she said. "Just because the association wasn't strong for cancer doesn't rule out a role for fruits and vegetables in cancer. Eating a healthy diet, for instance, may help prevent weight gain that we know is associated with cancer."
Maintaining a healthy weight, being physically active and not smoking are three very important lifestyle components that can reduce cancer risk, McCullough added.
The authors suggest the difference between their findings and previous work seeking associations between cancer and diet may be that many of the previous studies have been case-controlled, which means that participants reported their dietary intake after they were diagnosed with disease. This can lead to bias in recall and reporting. In this study, eating questionnaires were filled out by healthy participants before any illness was apparent.
Also a possibility, the authors add, is that cancer can take much longer to develop in the body compared to cardiovascular disease, and this study did not address eating habits before adulthood.
More information
The American Cancer Society offers information diet and cancer.
