Mothers’ Exposure to Some Chemical Compounds
Tied to Precocious Puberty
For the daughters of women accidentally exposed to a fire retardant chemical nearly three decades ago, the biological clock seems to be speeding up .
Precocious puberty is much more common among these young women, and a new study suggests that the change may be linked to their mothers’ contact with the chemical polybrominated biphenyl, or PBB.
That in turn raises the larger question, experts say, of environmental factors that slowly are lowering the age of puberty in North America.
In 1973, several thousand pounds of PBB accidentally were mixed with livestock feed that later was distributed to farms in Michigan. Over a million chickens, cows, pigs and sheep were contaminated, and the problem was identified when calves were stillborn or born with hoof deformities.
But by then, at least 4,000 people had been exposed to the chemical through meat and dairy products. PBB accumulates in fatty tissues around the body and can maintain its presence in people for roughly 13 to 29 years, depending on the level of exposure.
Researchers suspected that the chemical might interfere with hormone function, based on studies on animals, so they decided to check out the generation that followed those exposed in 1973.
They contacted all of the female children, now age 5 to 24, born to women exposed to the chemical in the Michigan incident. Those between 5 and 17 years of age filled out a questionnaire with their mothers, and those 18 and older were interviewed by phone. Information gathered included their age when menstruation started, current height and weight and a self-assessment of breast and pubic hair development in comparison with standardized drawings.
At the same time, led by associate professor of epidemiology Michele Marcus, the researchers estimated the daughters’ exposure in utero from blood serum measurements taken from their mothers after their exposure. The mothers’ levels during pregnancy were calculated based on how quickly PBB breaks down and leaves the body.
This was coupled with exposure via breast milk after birth.
Mothers with the highest levels of PBB in their blood, who also breastfed their daughters, produced girls with the earliest menstruation, the study says.
“PBBs … do get concentrated in breast milk,” Marcus says, because the chemical binds to fat cells and breast milk has a very high fat content.
Girls who received both in utero and breast milk exposure to the chemical started their periods at the average age of 11.6, compared to 12.7 years in girls who were not breastfed.
Little is known about exactly how PBBs might effect the onset of puberty, although experts say it is known that the chemical binds to estrogen receptors and that PBBs and polychlorinated biphenyls (PCBs) affect the thyroid gland.
Whether the chemical will clear the young women’s bodies before they reach their reproductive years also is not yet known, Marcus says. She plans further follow-up blood tests of the young women.
“The reason that this is important from a public health point of view is that it demonstrates that this type of chemical may be causing early puberty, and there are a lot of other chemicals in the environment that are more widely disseminated that may be acting similarly,” Marcus says. The young women in the study don’t meet the normal standards for precocious puberty, she says.
Marcia Herman-Giddens, an adjunct associate professor of maternal and child health at the University of North Carolina, calls this “a very serious public health issue.”
“It adds to the concern about what sort of effect these endocrine disrupters are having on people, especially children,” Herman-Giddens says.
Aside from isolated incidents like the one in Michigan, she says, the age of onset of puberty — the appearance of breast development and pubic hair — is falling in all North American girls. Menstruation now starts at an average age of 12, but a growing number of girls as young as 9 are beginning to have menstrual periods.
Source: Findings appear in a recent issue of Epidemiology.
