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Diabetes Tied to Colon Cancer in Men, Not Women

Posted Nov 02 2010 12:20pm

Tuesday, November 2, 2010
  Reuters Health Information Logo

By Amy Norton

NEW YORK (Reuters Health) - A new study confirms there is a link between type 2 diabetes and an increased risk of colon cancer -- but the added threat may be less than previous research has suggested, and seems to be fading among women.

A number of studies over the years have found that people with type 2 diabetes have a higher risk of developing colon cancer than those without diabetes. A 2005 "meta-analysis" combining the results of 15 previous studies found that men and women with diabetes were about one-third more likely to develop colon cancer than their diabetes-free counterparts.

However, a few studies since then have found a connection between diabetes and colon cancer among men, but not women.

The latest study, of more than 184,000 older U.S. adults followed for up to 15 years, has again found that men with type 2 diabetes, but not women, had higher odds of developing colon cancer.

Overall, researchers found, men with diabetes were 24 percent more likely to develop the cancer than those without diabetes. Meanwhile, men who used insulin -- a synthetic form of the hormone that regulates blood sugar -- showed a somewhat higher risk; they were 36 percent more likely to develop colon cancer than diabetes-free men were.

That excess risk linked to insulin use was quite small, though, and much less significant than some earlier studies have suggested, the researchers say.

"I think this is actually good news," lead author Peter T. Campbell said of the overall findings, which appear in the current issue of the journal Gastroenterology.

"The association with insulin use was modest," said Campbell, an epidemiologist with the American Cancer Society in Atlanta. Together with the findings from other studies in the past few years, he told Reuters Health, "This suggests that the association between diabetes and colon cancer among women is starting to disappear."

However, it is not yet clear why that is, according to Campbell.

One possibility is that women with diabetes are gaining better control of their blood sugar, he noted. An ongoing U.S. government study known as the National Health and Nutrition Examination Survey, for instance, found that between 1999 and 2004, women with diabetes showed an improvement in their hemoglobin A1C levels -- a marker of long-term blood-sugar control - whereas men did not.

Campbell speculated that women's gains in blood-sugar control might explain the fading link between diabetes and colon cancer.

It is not proven that diabetes or insulin use directly contribute to colon cancer in some people; studies such as the current one can only show an association between diabetes and the cancer; they cannot prove cause-and-effect.

But researchers suspect that diabetes might foster the cancer by chronically elevating blood levels of insulin and related hormones known as insulin-like growth factors; these hormones cause cells to grow and spread, and that may include cancer cells.

So it's possible, according to Campbell and his colleagues, that better blood-sugar control, which would mean lower insulin levels, could help lower any excess colon cancer risk.

Campbell noted that since the late 1990s, U.S. women's use of metformin -- an oral diabetes drug that helps lower blood sugar -- has been higher than that of men. It's plausible, he said, that this could be a factor in women's improved blood-sugar control.

A separate study announced this week at a meeting of the American College of Chest Physicians seems to support the theory. Cleveland Clinic researchers found that metformin users were less likely to develop lung cancer and, if they did, less likely to have advanced tumors that spread to other parts of the body. (See, "Diabetes drugs may help control lung cancer: study" at http://link.reuters.com/guh53q. (Story posted November 2, 2010 as 20101102elin009.)

The current colon cancer findings are based on a sample of 184,194 U.S. adults who were between the ages of 50 and 74 when they were recruited into the study in 1992-93. At the outset and periodically thereafter, the participants completed questionnaires on their medical histories, lifestyle habits and other health-related factors.

By 2007, 1,567 of the men were diagnosed with colon cancer. Of these, 227 cases were among the 6,529 men with type 2 diabetes (representing 3.5 percent of the diabetic men in the study population), and 1,340 cases were among the nearly 67,000 diabetes-free men (representing 2 percent).

When Campbell's team accounted for a number of other factors -- like the men's age, weight, education, family history of colon cancer and self-reported exercise habits -- men with diabetes were 24 percent more likely to develop colon cancer than their diabetes-free counterparts.

Women had lower rates of the cancer in general. There were 108 cases of colon cancer among the 4,800 women with diabetes (just over 2 percent), and 1,134 cases among the nearly 77,000 women without diabetes (1.5 percent). Once the researchers weighed other factors, there was no association between diabetes itself and women's colon cancer risk.

Campbell said that more research is needed to understand the reasons for the different findings in women and men. If better blood-sugar control is involved in the fading diabetes-colon cancer link among women, then that would have important implications for preventing cases of the cancer.

For now, Campbell advised people with diabetes to stick with their doctors' instructions on managing the disease -- which typically would include following a healthy diet, getting regular exercise, trying to shed excess pounds, and, often, using medication to keep blood-sugar levels in check.

SOURCE: http://link.reuters.com/kyh53q Gastroenterology, October 2010.

Reuters Health


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