Researchers at the American Institute for Cancer Research (AICR) think they may have uncovered one reason why overweight, inactive individuals have a higher risk for many cancers. They suspect that a major culprit is the increase in levels of insulin and other hormones often associated with excess weight. These higher levels—along with other conditions that collectively form what is known as “metabolic syndrome”—are also linked to cardiovascular disease and other chronic diseases.
“Research has demonstrated that insulin and other growth factors encourage cells to divide more rapidly,” says Helen Norman, PhD, lead author of a recent AICR study on cancer risk and obesity. “Under regular circumstances, release of insulin is tightly regulated and doesn’t pose much of a threat. But in many overweight, inactive people, the tissues are constantly exposed to high levels of insulin, which causes their cells to reproduce quickly and often.”
According to a November 16, 2001, AICR news release, cells that reproduce rapidly are more likely to sustain the types of mutations that can lead to cancer. Because not all overweight people have higher levels of insulin, it appears that genetics is also a factor. However, the AICR says it “just makes sense” for overweight individuals to adopt healthier lifestyle habits, since research has shown that insulin levels decline when weight decreases. In summary, the AICR researchers stress that high insulin levels are reversible and that diet, physical activity and weight management are all crucial in cancer prevention. Regular physical activity can help regulate insulin secretion, and weight loss can help restore insulin levels to normal.
In a related development, British researchers concluded that individuals who exercise regularly at moderately vigorous levels or greater had a lower overall risk of developing cancer than those who exercised less often or less intensely. The study, which appeared in the November issue of British Journal of Cancer, tracked middle-aged men over a period of almost 19 years. Those who worked out consistently and more intensely were significantly less likely to develop cancers of the stomach, esophagus or mouth. The researchers defined “moderately vigorous” exercise as activities such as swimming, jogging or running performed several times a week, according to an article that appeared in the February 2002 issue of HealthNews.