April 24, 2009 -- It's not just what you eat and how much you exercise that can pack on the pounds. What your mother consumed during her pregnancy may also add to your own waistline later in life.
A new study found that pregnant women who ate the most DDT-contaminated fish while pregnant in the 1970s had daughters that carried as much as 20 extra pounds three decades later. The study adds to growing evidence that chemicals in the environment can affect body weight and that conditions in the womb can have health effects in adulthood.
"The things that mothers are exposed to and that circulate in their blood while babies are in utero really do make a difference a long time later," said Janet Osuch, an epidemiologist at Michigan State University in East Lansing. "Obesity researchers have not looked at this at all."
In the early 1970s, the Michigan Department of Community Health began monitoring people who live along the shores of Lake Michigan. Industrial dumping in the lake, starting in the 1920s, has led to high levels of contaminants in the water, particularly of PCBs and DDE (the major breakdown product of the pesticide DDT).
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Over the years, periodic blood testing of Michigan residents helped confirm that people who ate lots of sport-caught fish from the lake harbored large burdens of PCBs and DDE in their bodies. These chemicals tend to magnify in fatty tissues as they move up the food chain. And they have been linked to all sorts of negative health problems.
Osuch and colleagues took the study one generation further. The researchers contacted more than 200 women who were daughters of the original study group. (The sons proved harder to reach, but may be the subject of a follow-up study).
Previous studies with some of these daughters, whose average age was now 30, found that those with the highest levels of prenatal exposure to PCBs and DDE started menstruating earlier, were able to get pregnant more easily, breastfed for shorter periods, and had higher levels of diabetes, among other conflicting and intriguing differences.
For the new study, Osuch and colleagues measured each woman's height, weight and body mass index. They conducted interviews by telephone and in person. And they looked back at blood tests taken form the mothers as close to pregnancy as possible.
The results, published in the journal Occupational and Environmental Medicine, showed no link between PCBs and weight. But women who had been exposed to more than 3 micrograms per liter of DDE while in the womb were now 20 pounds heavier than women who had been exposed to less than 1.5 mcg/L. Women in the middle group were 13 pounds heavier than women with the least amount of exposure.
"A high proportion of people have those levels," said John Vena, an epidemiologist at the University of Georgia in Athens. "It's quite provocative."
DDT was banned in the U.S. in 1973, but DDE remains in the environment for a long time, and the chemical is present, in varying levels, in just about everybody's blood, said Vena, whose own work has linked dioxins with diabetes.
"It's very persistent and ubiquitous," Vena told Discovery News. "It may help explain why the obesity epidemic is so persistent across the entire population."
Michigan, in particular, has one of the highest rates of obesity in the nation, Osuch said. It's too soon to conclude that prenatal DDE exposure caused the weight gain in these women, she added. But it's plausible: DDE is a known endocrine disruptor that interferes with the activity of estrogen. And women with low levels of estrogen often gain weight.
Current guidelines recommend eating no more than two servings of fish a week -- and sometimes less -- from certain lakes and rivers. Tuna and salmon are fatty fish that can contain lots of DDE, Osuch said. And pregnant women, the new work suggests, should be particularly cautious.
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