The Harvard study, published in the Journal of the National Cancer Institute (Vol. 96, No. 21:1577-1584), followed more than 100,000 participants for more than 10 years, periodically asking them what they ate and whether they had developed cancer, or had a stroke or heart attack.
Its findings support the 5-a-day recommendation, said senior author Walter Willett, MD.
"Our study means that everyone should still try to eat 5 or more servings of fruit and vegetables per day, but that the benefit will be mainly for cardiovascular disease," he said.
It's possible that fruits and vegetables do protect against cancer, he said, but the benefit is not as great as the public may believe. "Not smoking, avoiding [becoming] overweight, and staying physically active will be more effective in preventing cancer."