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What Can WHI Tell Us About Diabetes in Postmenopausal Women?

Diabetes was not a focus of the Women’s Health Initiative, but the massive amounts of data collected on 161,000 postmenopausal participants will probably be answering questions about women’s health for years to come.

WHI consisted of randomized trials to test the effects of hormone therapy, low-fat diet and calcium + vitamin D on heart disease, cancer and fractures, as well as an observational study examining the relationship between lifestyle, health and risk factors and specific disease outcomes. Participants ranged in age from 50 to 79 years.

This being the largest, most comprehensive examination of women’s health ever in the United States, researchers did gather information on diabetes diagnoses in the participants, providing data that could be examined in later analyses.

Among the diabetes-related findings:

Looking at diabetes prevalence and incidence by ethnicity, WHI measures were similar to those seen in the broader adult population – lowest in whites and a tad higher in Asians, even higher in Hispanics and most prevalent among African Americans.

Researchers found a somewhat lower rate of diabetes among women who took estrogen plus progestin hormone therapy compared to placebo. In the estrogen-alone trial, there was also a decrease in diabetes, but it was not statistically significant.

“No one would tell you to take hormones or prescribe them to prevent diabetes because this minimal effect is far overshadowed by adverse effects,” said Barbara Howard, senior scientist at the MedStar Health Research Institute and professor of medicine at Georgetown University School of Medicine. “But this gives us clues … and could lead to research on viable approaches to preventing diabetes.”

About those adverse effects: The WHI was famous for its findings that combination hormone therapy was associated with increased risk of heart attack, stroke, blood clots and breast cancer as well as reduced risk of colorectal cancer and fewer fractures compared to placebo. Estrogen-only therapy, meanwhile, was associated with increased risk of stroke and blood clots, uncertain effects on breast cancer and no effect on colorectal cancer risk, and reduced risk of fracture.

Among the 49,000 women randomized to a low-fat diet or comparison group and followed for about eight years, there was no impact found on the diabetes rate. At the time of the study design, the aim was to reduce all kinds of fat to 20 percent of the diet to test effects of this diet on cancer prevention. The intervention led to more weight loss than did the control condition. “Our conclusion was that low-fat dietary patterns can be a useful approach for weight loss in lifestyle programs designed to prevent diabetes,” Howard said.

The calcium and vitamin D trial provided no hints that vitamin D, even measured in blood samples, had any effect on the incidence of diabetes.

In looking at relationships between diabetes risk and physical activity and body mass index, researchers found that in all women, no matter their race, higher BMI and lower physical activity were strong predictors of risk for diabetes, and the combination was an especially strong predictor. And the evidence suggested that in this area, different racial groups will respond roughly the same to lifestyle interventions emphasizing more physical activity and lower weight.

When scientists adjusted the data, they saw a 28 percent increase in risk for developing diabetes in current smokers compared to never smokers. New quitters retained a relatively high risk, primarily because they tended to gain weight. Once the cessation period passed, the risk lowered dramatically.

Howard’s take on this: It’s never too late to obtain health benefits from quitting smoking.

-Emily Caldwell

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