Pregnancy raises risk of Type II diabetes

Science News, Nov 4, 1989 by K.A. Fackelmann

Pregnancy raises risk of Type II diabetes

Each successive pregnancy may slightly elevate a woman's risk of developing Type II diabetes later in life, according to a new epidemiologic study. If confirmed, the findings may eventually help unravel the mechanism underlying the development of Type II, or non-insulindependent, diabetes -- a condition less severe than insulin-dependent diabetes, usually affecting people after age 40.

Scientists know that obesity and a family history of diabetes increase a person's risk of getting Type II diabetes. Age also boosts the risk, because the pancreatic beta cells that produce insulin -- the hormone that helps the body use sugar -- work less efficiently as people get older. Past studies have hinted that pregnancy increases a woman's chance of later developing non-insulin-dependent diabetes, but many scientists pointed to weight gain during pregnancy to explain that association. Now, a report in the Nov. 2 NEW ENGLAND JOURNAL OF MEDICINE identifies pregnancy as an independent risk factor for Type II diabetes -- a risk not explained by obesity.

Donna Kritz-Silverstein, Elizabeth Barrett-Connor and Deborah L. Wingard of the University of California, San Diego, studied 1, 186 white, upper-middle-class women age 41 to 92. The scientists took reproductive and medical histories and calculated each volunteer's body mass index, a measure of obesity. When they gave subjects the glucose tolerance test, a standard measure of how well the body processes sugar, they found 326 women had impaired glucose tolerance -- flawed glucose metabolism that leads to Type II diabetes in some cases. And 146 other women had type II diabetes.

After controlling for age, obesity and family history of diabetes, the researchers found each pregnancy boosted a woman's risk of developing Type II diabetes after age 40 by 16 percent. Each pregnancy increased a woman's chance of develping impaired glucose tolerance by 10 percent, they found.

That risk may be important for women with multiple risk factors, comments Maureen I. Harris, an epidemiologist at the National Insitute of Diabetes and Digestive and Kidney Diseases in Bethesda, Md. A family history of diabetes remains the most important risk factor, she says. In the California Study, women with a family history of diabetes ran twice the risk of getting Type II diabetes compared with women who had no such history, Kritz-Silverstein says.

While women can't do anything about their inherited suceptibility to Type II diabetes, they can lower their risk by losing weight if they are obese, Harris says. And if further research confirms the link between pregnancy and diabetes, some women might consider keeping their pregnancy rate low. The number of children people have is a personal decision," Harris says. "But it seems to me it's important to know whether pregancny does lead to an increased risk for diabetes."

Although some women develop a temporary, mild form of diabetes during pregnancy, the California scientists did not determine the incidence of such "gestational diabetes" among women in the study. Many of the women bore their children before doctors began screening for gestational diabetes, Barrett-Connor says. Scientists know that women who get gestational diabetes run an increased risk of Type II diabetes as they age, she adds.

Barrett-connor and her colleagues speculate that pregnancy puts a strian on the mother's beta cells, a strain that can lead to Type II diabetes much later, especially if the woman is overweight or has inherited poorly functioning beta cells. During pregnancy, the researchers suggest, pancreatic beta cells must produce more insulin to keep the developing fetus nourished with a constant supply of glucose. At the same time, the mother's body tissue must become resistant to insuling to ensure that the extra glucose load goes to the fetus. Scientists know that Type II diabetcis have chronically high blood insulin levels and are insulin resistant, the California researchers note.