The Insulin Connection
One hormone may cause cancer, heart attacks, and many more ills.
Fortunately, doctors are starting to devise new ways to treat insulin resistance--which is sometimes called "metabolic syndrome" --with drugs and lifestyle changes. They are still working out all the connections, but already they have a list of some of the leading insulin-related illnesses:
Cancer
Insulin stimulates cell growth, and unfortunately cancer cells have six to 10 times the number of insulin receptors--molecules that grab on to the hormone--as do normal cells. So if extra hormone hits a pre-existing cancer cell, it makes a bad thing much, much worse. "For cancer, insulin is like pouring gasoline on a fire," says Edward Giovannucci, who studies the epidemiology of colon cancer at the Harvard School of Public Health.
Colon, breast, endometrial, pancreatic, and prostate cancers seem especially responsive. "We think breast cancer cells may have very special kinds of receptors, fetal insulin receptors, that are ultrasensitive to insulin," says Pamela Goodwin, director of the Marvelle Koffler Breast Center at Mount Sinai Hospital in Toronto. Insulin may also influence estrogen, another hormone that can trigger tumor growth. "So if you turn on one hormone, you turn on the other," Goodwin says. She is currently testing Glucophage to see if it can lower insulin levels in breast cancer survivors and plans to see if this affects cancer recurrence.
Cardiovascular Disease
High levels of insulin in the blood damage the lining of arteries, increase bad blood fats such as triglycerides and LDL cholesterol, and clump blood cells together so they are more likely to block up vessels. These observations prompted Gerald Reaven, the Stanford endocrinologist who first described insulin resistance in the 1980s, to finger the condition for heart attacks, strokes, and cases of high blood pressure.
Other research has come to back him up. A major study by Finnish researchers in the journal Circulation followed almost 1,000 men for 22 years and found insulin levels alone were the most powerful predictors of heart attack risk, especially in younger men. They were more powerful than obesity levels and physical inactivity, for example. Men with the highest insulin levels had more than three times the heart attack risk of those with the lowest.
The concept does have its critics. Last week in the journal Diabetes Care , Richard Kahn, chief scientific and medical officer for the American Diabetes Association, wrote an article questioning whether the idea of insulin resistance is truly useful, particularly when it comes to diagnosing and helping heart patients. Just calling something by a new name, he argues, doesn't change the recommended therapies. "I don't see the value . . . especially when the treatments are the same," says Kahn. He points out that if patients have high cholesterol, they're going to get cholesterol-lowering drugs and advice on diet and exercise, whether or not insulin resistance is the root cause.
But other experts see value in understanding insulin's role in the clustering of cardiovascular risk factors, particularly if it points the way toward new treatments. It's already doing that for stroke, for it's here that one new treatment is being tested. This spring the National Institutes of Health began a study at more than 60 research sites to see if the drug Actos, an insulin sensitizer, can reduce stroke recurrence in certain patients.
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