Exercise, weight control, adequate sleep found to reduce cancer risk

Washington -- "Keep moving to help ward off cancer" is a message that seems to be picking up momentum.

Evidence has built in recent years that risk for breast cancer, in particular, increases with a sedentary lifestyle, said several researchers at the American Assn. for Cancer Research's International Conference on Frontiers in Cancer Prevention Research. The meeting was held Nov. 16-19 in Oxon Hill, Md., outside Washington, D.C.

Numerous studies have shown that "fitness" and "fatness" both are important cancer risk factors, said Anne McTiernan, MD, PhD, director of the Fred Hutchinson Cancer Research Center's Prevention Center in Seattle.

With national obesity rates continuing to rise, Dr. McTiernan warned that breast cancer incidence could increase and that the prognosis for diagnosed cases could worsen. Several supporting studies, including findings from the World Health Organization's International Agency for Research on Cancer, conclude that excess weight and lack of physical activity account for one-quarter to one-third of breast cancer cases.

Dr. McTiernan cited research findings that breast cancer patients who are overweight and obese have poorer survival rates and increased chances of cancer recurrence compared with patients who weigh less.

Except for non-melanoma skin cancer, breast cancer is the most common form of cancer in U.S. women, according to the Centers for Disease Control and Prevention. The National Cancer Institute estimates that 182,460 women will be diagnosed with breast cancer this year, and 40,480 will die of it.

Several researchers explored ways to reduce those numbers. Findings from one study showed that regular physical activity can lower a woman's overall risk of cancer, but only if she also gets a good night's sleep.

James McClain, PhD, a cancer prevention fellow at the National Cancer Institute, found that although increased physical activity is associated with reduced cancer risk, including that of breast and colon cancers, additional research has shown that reduced sleep -- fewer than seven hours -- increases the risk of breast cancer.

McClain and colleagues followed nearly 6,000 women who enrolled in a 1998 study in Washington County, Md. All were cancer-free at the study's start. During the next 10 years, 604 cases of cancer were diagnosed, including 186 breast cancer cases.

The role of sleep

The researchers found that women who exercised the most had a greater reduction in cancer risk than did those who reported low exercise levels. While they also found that sleep was not independently associated with cancer risk, it does play a surprisingly large role. In fact, women who were the most active and were younger than 65 but reported sleeping less than seven hours a night had an increased risk of all types of cancer.

"These findings highlight the importance of being physically active with respect to reducing cancer risk and suggest that sleep, specifically duration, is also important. ... This interesting finding needs to be confirmed in subsequent studies," McClain said.

A study from Duke University's Center for Population Health and Aging in North Carolina also examined lifestyle factors and cancer risk, but focused on those older than 65. Among its conclusions: "Moderate physical activities are capable of decreasing cancer risk," said lead researcher Igor Akushevich, PhD, senior research scientist at the center.

The Duke researchers used data from the National Long Term Care Survey; Medicare; and the Surveillance, Epidemiology and End Results Program.