Certain pesticides are linked to hypothyroidism

A number of studies have associated certain pesticides with an increased risk of hypothyroidism and other thyroid diseases.

On of the most recent studies, published in the American Journal of Epidemiology (AJE), found that exposure to fungicides and organochlorine pesticides increased the rate of hypothyroidism among women by 20 and 40 percent, respectively.

Researchers at the University of Nebraska Medical Center derived these figures from medical data collected in the Agricultural Health Study (AHS), conducted in North Carolina and Iowa between 1993 and 1997.

All those enrolled in the AHS were the female spouses of agricultural workers. Nearly seven percent of them reported suffering from hypothyroidism. The typical rate of the disease among Americans is five percent, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

In the AJE, several agricultural chemical classes were not associated with hypothyroidism or hyperthyroidism. These included herbicides, fumigants, organophosphates, pyrethroids and carbamate.

However, any exposure to organochlorine pesticides or fungicides resulted in a higher rate of hypothyroidism. Organochlorine pesticides are a highly toxic class of neurotoxins that includes DDT, according to the University of Connecticut Center for Environmental Health.

Other studies have made similar associations between pesticides and thyroid disease. A 1998 study published in the journal Environmental Health Perspectives found that 10 percent of pesticides tested by the U.S. Environmental Protection Agency were carcinogenic in laboratory rodents.

A 2003 report in the Journal of Occupational and Environmental Medicine found that polychlorinated biphenyls (PCBs) - chemicals used to dilute pesticides - appear to affect the volume, hormone levels and the incidence of nodules in the thyroid glands of individuals most exposed to PCBs.

Hypothyroidism slows down many of the body's functions, resulting in fatigue, weight gain, brittle hair and constipation, the NIDDK reports. The report adds that women are more likely to develop the condition than men.