The familiar "eat right and exercise" message is particularly important for overweight elderly survivors of breast, prostate, and colorectal cancers, because lifestyle factors can significantly affect their quality of life, new research shows.

With more than half the 11 million cancer survivors in the U.S. older than age 65, Dr. Catherine E. Mosher, from New York's Memorial Sloan-Kettering Cancer Center, and her colleagues wanted to know whether overweight elderly cancer patients' quality of life — long after their original diagnosis and treatment — is affected by their health habits.

To study this question, they interviewed 753 men and women, all at least 65 years old, who had survived 5 or more years after a breast, prostate, or colorectal cancer diagnosis. All were overweight to some degree, but none was morbidly obese.

When the interviewers asked about exercise, diet, weight status, and quality of life, they found that half the group got no more than 10 minutes of moderate-to-vigorous exercise per week, and only 7% had healthful eating habits.

Overall, the researchers report in the journal Cancer, the survivors rated their mental and physical quality of life higher than average, compared to responses from age-matched normal populations.

However, those who exercised more and had better diet quality also had better physical quality of life outcomes (e.g., better vitality and physical functioning) than those who exercised less and ate poorly. Also, the greater the body weight, the poorer the physical quality of life.

In general, conclude Mosher and colleagues, the results point to "the potential negative impact of obesity and the positive impact of physical activity and a healthy diet on physical quality of life in cancer survivors.

It's already known that "physical activity is associated with a decreased risk of cancer recurrence and improved survival in both breast and colorectal cancer," Mosher told Reuters Health.

Another reason to exercise is that "Older cancer survivors are at higher risk for functional decline" - that is, the loss of their ability to perform their usual activities - compared to people of the same age who never had cancer, Mosher added.

Also, she said, "there's some evidence that physical activity may help prevent sarcopenic obesity," a form of obesity associated with chemotherapy and hormonal therapy.

"In terms of diet," she added, "it remains unclear whether following specific dietary guidelines improves outcomes in quality of life for specific cancers."

Even so, Mosher said, being overweight will worsen a variety of other medical conditions a cancer survivor might have.