New research has linked exposure to a frequently used group of pesticides called pyrethroids -- also found in domestic products like mosquito sprays and head lice shampoos -- with the early onset of puberty in boys. The study was presented at the Endocrine Society's 99th annual meeting, April 1-4, in Orlando, Florida, USA.
Researchers at Zhejiang University in Hangzhou, China, studied the effect of a class of pesticides called pyrethroids on puberty in 463 Chinese boys aged between nine and 16 years old.
This class of pesticides accounts for more than 30% of global insecticide use, the researchers noted. Pyrethroids are difficult to avoid, as they are present in soil, air and water. Previously, these chemicals have been associated with a toxic effect on the nervous system, provoking cognitive problems, notably in children.
This latest study suggests that pyrethroids could stimulate testosterone production in boys by increasing levels of two hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
A 10% increase in a pyrethroid metabolite called 3-PBA, present in participants' urine, was associated with a 4% increase in levels of LH and FSH.
An increased level of 3-PBA in urine raised the chance of boys being at an advanced stage of genital development by 73% to 110%, the researchers explain.
Currently, few studies have assessed the direct impact of the environment on health, other than for people directly exposed to pesticides or toxic substances, like farmers. However, these synthetic products are considered a risk factor.
Even at very low doses, they can have serious effects, notably in fetuses, embryos and young children. Genital defects, early menopause and puberty, and infertility can be consequences of exposure to these substances.
Early puberty is associated with a risk of diseases in adulthood, notably testicular cancer in boys and breast cancer in girls, as well as behavioral problems, high blood pressure, diabetes and heart issues.