Dr Whitney Goldner and colleagues of the University of Nebraska Medical Center in Omaha 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% of the women reported having thyroid disease (7% underactive thyroid glands; 2% overactive thyroids) whereas, in the general population the rate of diagnosed thyroid disease ranges from around 1 – 8%

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 (now rarely used in the US) were 1.2 times as likely to have hypothyroidism. 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.

American Journal of Epidemiology, online January 8, 2010.

Courtesy Reuters

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First Published in January 2010

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