Controlling Diabetes May Reduce Cancer Risk and Death

There are myriad benefits from avoiding diabetes through exercise, diet and maintaining a healthy body weight. A new NIH-AARP Diet and Health Study has confirmed additional benefits in the form of reduced morbidity and mortality from certain cancers.

Diabetes is associated with lower risk of prostate cancer in men but with higher risk of other cancers in both men and women, and the results provide further evidence that abnormal insulin and glucose signaling may contribute to cancer initiation and development. Previous epidemiologic studies have also shown an association between diabetes and an increased risk for cancers including colorectal, liver and pancreas.

Diabetes Associated With Increased Cancer Risk

The 11-year prospective study followed more than 500,000 patients ‒ predominantly white, non-Hispanic men and women aged 50 to 71 years ‒ from 1995 to 1996. The results showed that diabetes was associated with an 8 percent increased risk for cancer among women and a 4 percent decreased risk for men.

In previous research, a decreased risk for prostate cancer was associated with diabetes, which researchers believe might be due to the lower testosterone levels associated with diabetes. After excluding prostate cancer from their evaluation, the researchers found that diabetes was associated with a 9 percent increased risk for cancer in men.

As for mortality, diabetes was associated with an 11 percent increased risk in women and a 17 percent increased risk in men. These risks appeared independent from other cancer risk factors, such as obesity and cigarette smoking.

After evaluating by cancer site, the researchers found diabetes was associated with a significant increase in risk for colon, rectal and liver cancers among men and women. In men, diabetes was associated with an increased risk for pancreatic and bladder cancers. In women, it was associated with an increased risk for stomach, anal and endometrial cancers. No association was found between diabetes and lung, skin or other cancers.

Earlier research has also linked obesity, diabetes and metabolism to cancer risk with the findings linking weight gain and diabetes to a variety of cancers affecting both men and women, including breast, prostate and colorectal cancer.

Colorectal Cancer & Type 2 Diabetes Share Common Factors

Women with diabetes are 1.5 times more likely to develop colorectal cancer than those who do not have the metabolic disorder. The findings add to the complex body of evidence linking diet and colorectal cancer and also provide new evidence that furthers our understanding of the role of insulin in cancer promotion.

It has been determined that colorectal cancer and type 2 diabetes share a number of common factors, including obesity, so it is interesting to see the direct line between these two conditions. In general, the idea is that if elevated insulin levels create a biochemical environment conducive to cancer growth, it provides one mechanism by which diet and lifestyle can really influence cancer risk.

Data from a massive screening study called the Breast Cancer Detection Demonstration Project, initiated at 29 centers throughout the United States in the 1970s involving more than 45,000 study participants with no history of colorectal cancer or self-reported diabetes for eight years (from 1987-1989 and from 1995-1998), was used to identify which of them subsequently developed colorectal cancer.

According to the findings, women with diabetes had a greatly increased risk of developing colorectal cancer. These results remained statistically significant even after controlling for all known and suspected confounding variables.

However, it is not exactly clear what aspect of diabetes is the underlying cause for this increased risk but one hypothesis centers on the elevated concentration of insulin typically seen in people with type 2 diabetes. In the early stages of the disease process, people become insulin resistant, meaning they must produce more and more insulin to regulate their blood sugar.

Pre-Diabetics Also at Increased Risk

Even after frank diabetes begins, insulin levels remain chronically elevated for extended periods before the pancreas can no longer supply the level of insulin the body demands. So, if the elevated insulin is the problem, then pre-diabetics, who are also hyper-insulinemic, should also be at increased risk for developing colorectal cancer.

To test that idea, the researchers re-analyzed the data, this time including women who were likely pre-diabetic at the beginning of the follow-up period. The idea was that these women were likely hyper-insulinemic at that stage. Surprisingly, the elevated risk, while still significant, had dropped slightly in comparison with that of known diabetics.

This suggests that either the pre-diabetic women had not had elevated insulin long enough or intensely enough to increase risk as they observed in the diabetic women, or alternatively, something other than or in addition to hyper-insulinemia could explain the significant, increased risk for colorectal cancer observed in people with diabetes.

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