High insulin levels caused by inactivity and excess weight may make cancer more likely, according to scientists with the American Institute for Cancer Research, or AICR.
AICR researchers say their new theory based on a review of scientific literature dealing with obesity and cancer risk could provide the “missing link” that explains why cancer is more common among the overweight and the obese.
AICR, the nation’s third largest cancer charity, is not suggesting high levels of insulin a hormone crucial for the metabolism of glucose and carbohydrates are responsible for all cancer.
The institute focuses exclusively on the link between diet and cancer, and the only research it funds examines how diet and nutrition affect cancer risk.
However, Helen Norman, lead author of the new AICR report that sees high levels of insulin and other hormones known as “growth factors” as culprits in the increased risk of cancer among overweight, sedentary people, says there is growing support for this thinking.
Dr. Rowan Chlebowski, chief of UCLA’s Department of Medical Oncology and Hematology, says, “Insulin levels have already been associated with diabetes, heart disease, stroke, cognitive dysfunction and overall mortality.
“It should come as no surprise that new research is now implicating this same insulin-regulatory pathway in several kinds of cancer,” he added.
Dr. Chlebowski was referring to research showing that two related conditions, known as insulin resistance and hyperinsulinemia, may be connected to malignancies such as breast and colon cancer.
Insulin resistance is marked by a growing inability to use insulin. It’s a condition that tends to follow weight gain particularly weight in the stomach area and a drop in physical activity. It is often associated with higher-than-normal cholesterol and blood-sugar levels.
“As their bodies become less sensitive to insulin’s effects, overweight and obese individuals experience greater difficulty converting glucose into energy,” AICR said in a statement.
“The body attempts to compensate for this by producing more insulin, a condition called hyperinsulinemia, which, in turn, spurs cells to divide and raises cancer risk,” the cancer research organization added.
“It’s clear that high insulin levels coincide with a host of chronic diseases, including cancer,” said Dr. Gerald Reaven, professor emeritus of medicine, endocrinology, and metabolism at Stanford University.
Dr. Reaven, best known for research showing that elevated insulin levels promote heart disease, said, “We’ve just published a paper showing that insulin resistance is a good predictor of cancer risk. But the situation is complex.”
He said it is important to recognize that “genetics [also] plays a role” in determining whether someone becomes insulin resistant.
The genetic factors, Dr. Reaven said, have “historically made the precise impact of weight and fitness harder to gauge.”
“But I hasten to add that it is now very clear that insulin resistance is more common among overweight people, and that’s important,” the veteran researcher said.
AICR says that while insulin resistance is a “potentially dangerous condition,” it is “reversible.” It can be undone, the organization says, through regular physical exercise and by losing weight and keeping it off.