Fruits and Vegetables Have Only Weak Effect in Cancer Prevention

Zosia Chustecka

April 08, 2010

April 8, 2010 — Eating more fruits and vegetables has only a modest effect on reducing the risk of developing any cancer, a new study reports. But the public health message to eat more fruits and vegetables still holds, because of benefits to cardiovascular health, say experts.

The finding was reported online April 6 in the Journal of the National Cancer Institute, and comes from the massive European Prospective Investigation Into Cancer and Nutrition (EPIC) study, which involved 478,478 people followed for a median of 8.7 years.

People who ate an extra 200 g of fruits and vegetables — equivalent to about 1.5 or 2 extra servings — showed a small but statistically significant 4% reduction in the risk of developing any cancer.

"We found a linear relationship, so no matter where you were in your fruit and vegetable intake, if you increase it by 200 g, then you would have this 4% reduction," lead author Paulo Boffetta, MD, from the Mount Sinai School of Medicine in New York City, explained in an interview. Only about 20% of the study participants ate the recommended 5 portions of fruits and vegetables each day, he noted.

"We found some effect, but a weak one; this is not surprising overall," he said.

Dr. Boffetta explained that there was a prevalent view up until about 10 to 15 years ago that fruits and vegetables were protective against cancer, but then came studies — mainly from the United States — which showed no effect at all, so opinion has swung back and forth. "Our finding probably falls in the middle ground," he added.

When asked if he thought that the reduction seen in this study was a true effect, Dr. Boffetta said the only way to be certain is to conduct a randomized trial, and the current study is observational. But he added that the fact that the finding was statistically significant suggests that it is not likely to be due to chance.

No Need to Change Public Health Message

There are no results yet from the EPIC study on cardiovascular health, but other studies have shown the benefit of eating fruits and vegetables on cardiovascular health, and this benefit seems to be "bigger and more consistent " than any effect on cancer prevention, Dr. Boffetta pointed out. "So the message about eating fruits and vegetables still holds," he said.

"There is no need to modify the message, because the overall effect is beneficial," he continued. "The message to the public should be to eat as many fruits and vegetables as possible."

Walter Willet, MD, PhD, a leading expert on diet and cancer from the Harvard School of Public Health in Boston, Massachusetts, agrees.

"Recommendations and actions to increase intake of fruits and vegetables have a sound basis," he writes in an accompanying editorial. Even as the evidence of a benefit against cancer has been waning, the data supporting a cardiovascular benefit have been accumulating, he notes.

The EPIC trial "strongly confirms the findings from other prospective studies . . .  that any association of intake of fruits and vegetables with risk of cancer is weak at best," Dr. Willet writes.

"A broad effort to increase consumption of fruits and vegetables will not have a major effect on cancer incidence," he continues. However, "such efforts are still worthwhile because they will reduce the risk of cardiovascular disease, and a small benefit for cancer remains possible."

But for the prevention of cancer, the primary focus should be heightened efforts to reduce smoking and obesity, Dr. Willet concludes.

Specific Foods, Specific Times

The wide scope of the question addressed in many studies in this field — i.e., the effect of eating fruits and vegetables on the risk of developing any cancer — might dilute benefits from specific foods, Dr. Willet suggests in his editorial. Dr. Boffetta told Medscape Oncology that he wholeheartedly agrees with this.

It might be that a small group of fruits and vegetables, or some specific substance in some of these foods, has a protective effect, Dr. Willet writes. As an example, he cites the "considerable evidence" suggesting that lycopene and tomato products reduce the risk for prostate cancer.

In addition, there might be an element of timing that has been missed. Multiple lines of evidence indicate that ionizing radiation and some other risk factors for cancer operate primarily in childhood and early adulthood, Dr. Willet points out. Thus, antioxidants and other protective constituents of fruits and vegetables might need to be present at that time to be effective.

Unfortunately, EPIC and almost all studies of diet and cancer would have missed such effects because they start decades later in life, he points out.

The researchers have disclosed no relevant financial relationships.

J Natl Cancer Inst. Published online April 6, 2010. Abstract


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