November 19, 2001
New Theory May Provide Missing Link Between Overweight,
High Insulin Levels Caused by Inactivity, Excess Weight Make Cancer More
Likely, Scientists Say
- A specific condition that occurs in the bodies of many inactive,
overweight individuals may actually encourage the cancer process, according
to researchers at the American Institute for Cancer Research (AICR).
Past studies have shown that overweight, inactive individuals have higher
risk for many cancers, but a clear biological explanation for exactly why
this is so has been more elusive.
Now, research is showing that being overweight and inactive can cause the
body to release high levels of insulin and other hormones known as "growth
factors." High insulin levels -- along with several other conditions
collectively known as "metabolic syndrome" or "syndrome X" -- have already
been linked to cardiovascular disease and other chronic diseases.
Many cancer scientists now believe this same state of affairs is one reason
cancer is more common among the overweight and obese.
"Insulin and other growth factors encourage cells to divide more rapidly,"
said Helen Norman, Ph.D., lead author of a new AICR review of the scientific
literature on obesity and cancer risk.
"Under normal circumstances, release of insulin is tightly regulated and
doesn't pose much of a risk. But in many overweight, inactive people, the
tissues are constantly exposed to high levels of insulin, which causes cells
to reproduce quickly."
Whenever cells reproduce rapidly, Dr. Norman said, the chances increase that
something could go wrong in the process, such as the kind of random mutation
that can lead to cancer.
But AICR researchers stress that this potentially dangerous condition is
* Regular physical activity can help reset the body's hormonal systems and
regulate the secretion of insulin and other growth factors.
* Losing weight and keeping it off also helps restore insulin levels to