The age of puberty has been falling for some time. There has been much debate about causes, as well as the possible consequences. The annual meeting of the Endocrine Society has heard the blame for boys, at least in part, may lie with common pesticides.
Early puberty has been shown to be associated with higher risks of testicular and breast cancer. Concerns, however, have tended to focus on psychological costs, with children presumably even less equipped to deal with the raging emotions and sexual desires associated with puberty than teenagers. Most research, and public concern, has focused on girls.
Although part of the increase in early puberty appears to be an unfortunate side effect of a desirable trend – better nutrition from birth – factors we might wish to reverse may also contribute. Dr Jing Liu of the Zhejiang University, China, studied the influence of pyrethroids, a widely used class of pesticides.
Liu found 463 Chinese boys aged 9-16 showed a 4 percent increase in two hormones known to spark testosterone production in men for each 10 percent increase in the molecule 3-PBA in their urine. 3-PBA, also known as 3-phenoxybenzoic acid, is produced after exposure to pyrethroids with a short half-life in the human body. High 3-PBA drastically increases the chance of early genital development.
"We recognize pyrethroids as a new environmental contributor to the observed trend toward earlier sexual maturity in boys," Liu said in a statement. Liu also showed that cypermethrin, a common pyrethroid, accelerates the onset of puberty in male mice.
Pyrethroids join the growing class of chemicals identified as endocrine disruptors for their effects on hormone secreting glands. A media conference summarized four endocrine disruptor studies presented at the conference earlier his year, Liu's among them. Other studies implicated endocrine disruptors in rising rates of thyroid cancer, triggering breast cancer, and altering gene expression linked to fatty livers.
Phasing out pyrethroid use will be challenging, however. They account for an estimated 30 percent of global insecticide use, widely used both on crops and to kill insects indoors, having the advantage of breaking down quickly on exposure to sunlight.
The problem is that it is very hard to find chemicals that kill insects that are not also bad for vertebrates, ourselves included. We share a common ancestor with insects, and even though it was a long time ago, most things potent enough to kill them quickly have harmful effects on us as well. With America's newly appointed EPA head Scott Pruitt having rejected the advice of the EPA's own scientists to ban chlorpyrifos, a less common pesticide shown to have even more serious effects on children, the chances of imminent action on pyrethroids look slim.
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