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High Insulin Levels Linked to Pancreatic Cancer

Study of male smokers saw twofold risk increase for those with highest levels

TUESDAY, Dec. 13, 2005 (HealthDay News) -- Elevated blood levels of insulin do more than increase diabetes risk, they may also increase odds for pancreatic cancer.

New research found that male smokers with the highest post-fasting blood insulin levels had double the risk of pancreatic tumors.

"We had known that there was a pretty consistent association between diabetes and glucose intolerance and pancreatic cancer, but the reason for that association has been somewhat controversial," explained study author Rachael Stolzenberg-Solomon, an investigator in the nutritional epidemiology branch at the National Cancer Institute. "Some people feel that diabetes is a risk factor for pancreatic cancer, while some clinicians think some cases of diabetes are the result of latent pancreatic cancer."

This study's findings, said Stolzenberg-Solomon, support the hypothesis that the high levels of insulin that occur during the early stages of diabetes may promote the growth of pancreatic cancer cells.

The findings appear in the Dec. 14 issue of the Journal of the American Medical Association.

More than 32,000 Americans will be diagnosed with pancreatic cancer this year and most will die because the disease is usually detected far too late, according to the American Cancer Society (ACS). Cigarette smoking is responsible for almost one in three cases of pancreatic cancer, according to the ACS.

Because many pancreatic cancers aren't found until the later stages of the disease, the prognosis for this type of cancer is grim. Five-year survival rates range between 4 percent and 15 percent, depending on how far the disease has spread at the time of diagnosis.

The current research culled data from a large Finnish study on more than 29,000 male smokers aged between 50 and 69 years at the start of the study. From the pool of 29,000, the researchers found 169 cases of pancreatic cancer that occurred after the fifth year of follow-up.

One reason the researchers only looked at cancers that occurred after five years of follow-up was to better assess if early diabetes might be contributing to the cancer. They could assess this because they had blood samples from each man to measure glucose and insulin levels.

The researchers also randomly selected 400 men from the larger sample to act as controls.

Men with the highest levels of insulin in their blood and men with clinically diagnosed diabetes had double the risk of pancreatic cancer, compared to men with low levels of insulin and no history of diabetes.

"This is the first study to show that insulin levels are increased with the risk of pancreatic cancer," said Eric Jacobs, a senior epidemiologist for the American Cancer Society.

Jacobs was quick to point out, however, that insulin injected for the treatment of diabetes is not being implicated as a risk factor for pancreatic cancer in this study.

The suspected mechanism behind the increase in risk is that "pancreatic cells are exposed to a lot of insulin because insulin is produced in the pancreas. People with diabetes inject insulin into other locations, so the pancreatic cells aren't exposed to as much insulin," Jacobs explained.

Both Stolzenberg-Solomon and Jacobs said that this study's findings likely apply to women and nonsmokers as well.

The findings suggest that increasing levels of physical activity might help prevent pancreatic cancer, along with reducing your risk of diabetes and other serious illnesses, according to Jacobs.

"Exercising more can help reduce levels of insulin," said Jacobs.

"While our study needs to be confirmed, it has potentially important implications for nutrition and pancreatic cancer prevention strategies," said Stolzenberg-Solomon.

"Lose weight, increase your physical activity and maybe make other changes to your diet, like eat less saturated fat. These changes impact other cancers and other chronic disease," she said.

More information

The National Cancer Institute has more information on pancreatic cancer.

SOURCES: Rachael Stolzenberg-Solomon, Ph.D., M.P.H., R.D., investigator, Nutritional Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Md.; Eric Jacobs, Ph.S., senior epidemiologist, American Cancer Society, Atlanta; Dec. 14, 2005, Journal of the American Medical Association
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