July 4, 2013
U.S. children who were exposed in the womb to high levels of DDT, PCBs and other chlorinated chemicals in the 1960s were not more likely to be obese, according to new research.
One substance, dieldrin, was linked to higher odds of obesity in children but the number of children studied was small.
Fhardseen/flickr Multiple causes of childhood obesity may include prenatal exposure to chemicals.
It is the largest study examining the link between organochlorine chemicals and childhood obesity, and the first to associate obesity with prenatal exposure to the pesticide dieldrin. Previous studies have reached conflicting conclusions.
Organochlorines were widely used as pesticides and industrial compounds in the 1940s through 1970s. Most uses have been banned for decades. However, traces of these chemicals are still found in most people’s bodies today because they persist in the environment and accumulate in fatty tissues.
Childhood obesity is an increasing problem worldwide. In the United States, 4 percent of children aged 6 to 11 were obese in the early 1970s compared with 20 percent in 2008. Researchers have been examining the role that prenatal exposure to potentially hormone-altering chemicals – such as organochlorines – may play.
The epidemiologists used data from the U.S. Collaborative Perinatal Project, which enrolled pregnant women from 1959-1965. The women’s blood was measured in their third trimester for DDT, polychlorinated biphenyls (PCBs) and other chlorinated chemicals. Then the researchers checked records for 1,915 of the women’s children to determine how many were obese at the age of 7.
Prenatal exposure to all but one of the chemicals was not associated with obese or overweight children. However, for dieldrin, children in the two groups of highest exposure were 3.6 and 2.3 times more likely to be obese than those in the lowest exposure group.
Only 89 children were in the two highest exposure groups. “The suggestive association between dieldrin and childhood obesity was perhaps a chance finding given the number of analyses we performed,” the authors wrote in the paper published in Environmental Health Perspectives.
Dieldrin was widely used as a pesticide from about 1950 to 1974 but was banned from almost all uses in the United States in 1985, according to the U.S. Environmental Protection Agency.
The pregnant women in this study had much higher levels of all the chemicals tested (hexachlorocyclohexane, DDE, DDT, dieldrin, heptachlor epoxide, hexachlorobenzene, trans-nonachlor, oxychlordane and PCBs) than people do today.
The researchers controlled for mothers’ race, education, pre-pregnancy weight, smoking status and the child’s birth order.
Previous research linking the chemicals to children’s body weight has been inconsistent. DDE exposure was linked to a higher body mass index for children, according to a 2011 study, but the link was dependent upon maternal smoking. HCB exposure was linked to obesity and higher body mass index for children in a 2008 study. The children were exposed to higher levels than in the current study.
It is unclear how organochlorine chemicals might affect a child’s body weight. But previous research has suggested that they could alter the hormones that regulate growth or alter the functioning of the central nervous system.
Most studies have focused on high levels of exposure. In light of this, the authors of the current study said they could not rule out the possibility that prenatal exposure to low levels of organochlorines could spur obesity. Some research has shown that small doses of hormone-like substances can have effects that large doses do not.
The study was a collaboration of scientists from Mexico’s National Institute of Public Health, the U.S. Centers for Disease Control and Prevention, the National Institute of Environmental Health Sciences and Ohio State University.