Exposure To Pesticides Increases
Risk of Underactive Thyroid
Exposure to certain types of pesticides could up the risk of
thyroid disease in women, according to a new study of thousands
of women married to licensed pesticide applicators.
Problems with the thyroid gland are more common among women than
men, Dr. Whitney S. Goldner of the University of Nebraska Medical
Center in Omaha and colleagues note in their report. The thyroid
is located at the base of the throat and plays an important role
in regulating the body's energy use.
There is growing evidence for a link between exposure to pesticides
and thyroid problems, the authors note. They studied more than
16,500 women living in Iowa and North Carolina who were married
to men seeking certification to use restricted pesticides in those
states during the 1990s.
Overall, 12.5 percent of the women reported having thyroid disease;
7 percent had underactive thyroid glands (hypothyroidism) and
2 percent had overactive thyroids (hyperthyroidism).
In the general population, Goldner and colleagues point out,
the rate of diagnosed thyroid disease ranges from around 1 percent
to 8 percent.
When they looked at 44 different pesticides, they found that
women married to men who had ever used organochlorine insecticides
-- such as aldrin, DDT, and lindane -- were 1.2 times as likely
to have hypothyroidism. (Some of these pesticides are no longer
used in the U.S. and elsewhere, although lindane is available
in some states as a treatment for head lice.)
The risk of hypothyroidism for women exposed to fungus killers
was 1.4-fold greater.
Specifically, they found that chlordane, an organochlorine pesticide,
was associated with a 1.3-fold hypothyroid risk. The fungus killers
benomyl and maneb/mancozeb were associated with tripled and doubled
risk, respectively, and the herb killer paraquat nearly doubled
the likelihood of hypothyroidism.
Maneb/mancozeb exposure increased women's risk of hyperthyroidism
more than two-fold; it was the only chemical studied that upped
the risk of both hypothyroidism and hyperthyroidism.
It's not clear why pesticides would be linked to thyroid problems.
However, some studies have suggested that such chemicals have
low levels of certain thyroid hormones.
Goldner's team cautions that their study was not designed to
tease out cause and effect. Similarly, because it was based on
reports from subjects rather than more definitive information
such as blood tests, further study is needed before calling the
SOURCE: American Journal of Epidemiology, online January 8, 2010.
February 25, 2010