By Charnicia E. Huggins
NEW YORK (Reuters Health) – While infertility may be caused
by a number of factors, new study findings suggest that
exposure to nonpersistent, or short-lasting, insecticides may
play a role in male infertility.
“Environmental exposure to chlorpyrifos or its metabolite
(TCPY) may be associated with reduced levels of circulating
testosterone in adult men,” lead study author Dr. John D.
Meeker, of the University of Michigan, Ann Arbor, told Reuters
Health. “A decline in testosterone throughout a population
could potentially lead to adverse reproductive health
outcomes,” he added.
Until 2000, chlorpyrifos was one of the most common
insecticides used in homes. The Environmental Protection Agency
restricted its residential use to reduce children’s exposure to
the chemical after research revealed it can affect the central
nervous system. Just one year earlier, however, up to 19
million pounds of the chlorpyrifos were used in the United
States, and recent investigations suggest that individuals
still experience environmental exposure to the substance,
despite EPA restrictions.
The Second National Report on Human Exposure to
Environmental Chemicals found that more than 90 percent of men
had detectable levels TCPY in their urine.
In a previous report, Meeker and his colleagues found that
higher levels of 1-naphthol (1N) in men’s urine are associated
with decreased sperm concentration and motility and increased
DNA damage in sperm cells. 1N is a breakdown product of
carbaryl, a lawn and garden insecticide known as Sevin, and the
compound naphthalene, which is found in cigarette smoke, diesel
fuel and other combustion byproducts.
Meeker and his colleagues from the Harvard School of Public
Health in Boston and the Centers for Disease Control and
Prevention in Atlanta explored the association between TCPY and
1N, and reproductive hormone levels in 268 men who were
recruited at an infertility clinic between 2000 and 2003.
Men with higher urine levels of TCPY and 1N had lower
levels of the sex hormone testosterone, the researchers report
in the journal Epidemiology. The association with TCPY was
dose-dependent, such that testosterone levels decreased along
with increasing levels of TCPY.
Higher TCPY levels were also associated with a decreased
free androgen index, a marker of lower testosterone
concentrations, the report indicates.
“Although the decrements in testosterone related to TCPY
were relatively small,” Meeker acknowledged, “they may be of
public health concern because of widespread human exposure
among men.”
The researchers also found some evidence that higher TCPY
and 1N levels may be associated with decreased levels of
luteinizing hormone and a decreased free androgen index, but
more studies are needed to confirm this finding.
If TCPY and 1N are associated with decreased levels of both
testosterone and luteinizing hormone, the hypothalamus and the
pituitary gland, rather than the testes, may be involved in the
mechanism by which certain pesticides affect sperm quality,
Meeker speculates. “But there are several other potential
mechanisms as well,” he said.
According to Meeker, “This is the first human evidence of
an association between chlorpyrifos or its metabolite (TCPY)
and testosterone levels, so other studies would be needed to
substantiate our findings.”
SOURCE: Epidemiology, January 2006.
Comments