Exploring Why Gestational Diabetes Leads to Type 2
Harvard researcher Frank Hu taps important diabetes and pregnancy data
Frank Hu, MD, MPH, PhD
Professor, Harvard School of Public Health
Epidemiology and Nutrition
ADA Research Funding
Bringing a new life into the world is tough on the female body in many ways and amounts to a stress test for the beta cells that produce insulin. Beginning in the second trimester, hormonal and physical changes might result in increased insulin resistance. The condition resembles type 2 diabetes and is known as gestational diabetes.
Gestational diabetes affects up to 9 percent of pregnant women, according to a recent study by the Centers for Disease Control and Prevention, and its symptoms often disappear within weeks of giving birth. “After pregnancy, through appropriate diet and exercise and medications, women can become nondiabetic,” says Frank Hu, MD, MPH, PhD, professor of nutrition and epidemiology at the Harvard School of Public Health.
But it’s not to be underestimated—particularly because there’s evidence that gestational diabetes puts both mother and child at risk. Researchers are realizing that gestational diabetes leaves a mark. Somehow it increases the likelihood that women will develop type 2 diabetes later in life. “They have a three- to sevenfold higher risk of developing type 2 within five to 10 years,” Hu says. “We’re trying to figure out why.”
With the help of a grant from the American Diabetes Association, Hu is tapping one of the most ambitious health studies ever attempted. Funded by the National Institutes of Health, the long-term Nurses’ Health Study started in 1976 as a way to study cancer risk factors. Since then, more than 200,000 female nurses from all 50 states have taken part, answering regular, detailed questions about everything from smoking habits to diet, exercise, and disease.
The rich data are a researcher’s dream. “One of the advantages of having nurses is they’re very motivated and provide high-quality data about their medications and medical conditions,” Hu says.
Hu has been looking at a small subgroup: participants who experienced gestational diabetes during one or more pregnancies. “We followed 6,000 women,” he says. “We’ve been following them for 10 years and have collected detailed data on diet and exercise before and after pregnancy.”
In addition to detailed questionnaires, the study collects blood and urine samples from participants, which gives Hu and other researchers a window into their genes. That, in turn, might make it possible to see if there are genetic factors that put some women at higher risk for type 2 once they’ve had gestational diabetes.
There’s another intriguing possibility Hu is looking at: Perhaps, he says, there are environmental factors that play a role as well.
We’re used to thinking about genes as destiny, unchangeable and fixed. But there’s evidence that the effect of our genes isn’t static—and to some extent, it may be under our control. Like flipping a switch, outside factors can turn genes on and off, affecting how they “express” themselves. “We’re talking about behavior and lifestyle: diet, smoking, physical activity, sleep, stress,” Hu says. “To some degree, we can modify the expression of our genes.”
One example is the recent discovery—based on data from the Nurses’ Health Study—that sugary beverages can influence the genetic effects of obesity. Drinking soda, in other words, “amplified the effects of obesity genes,” Hu says. “One of the main implications is that genes are not destiny. What we eat [and] what we do can modify how our genes are expressed or activated. It’s more evidence for adopting a healthy lifestyle.”
For women who want to get pregnant—or already are—Hu’s research suggests there’s even more reason to make healthful lifestyle choices. By drilling down into the data to see what nurses who avoided the progression from gestational diabetes to type 2 have in common, Hu hopes to find even more specific recommendations to help pregnant women stay healthy after they give birth. “We want to identify what specific dietary and lifestyle changes before pregnancy can reduce the chances of getting gestational diabetes,” he says, “and understand how to reduce the progression from gestational diabetes to type 2 diabetes.”
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