New Study Links Pesticide Use to Thyroid Disease in Women

(Beyond Pesticides, February 22, 2010)

Wives of agricultural pesticide applicators have a significantly increased risk of developing thyroid disease, according to the new study, “Pesticide Use and Thyroid Disease Among Women in the Agricultural Health Study,” published in the American Journal of Epidemiology. Using data collected from more than 16,500 female spouses from Iowa and North Carolina enrolled in the Agricultural Health Study from 1993 to 1997, the researchers show that 12.5 percent of the women have thyroid disease, 6.9 percent have hypothyroidism and 2.1 percent have hyperthyroidism; whereas, the national average is 5 percent and 1 percent, respectively. Thyroid disease is more common in women than men and is the second most common hormone disorder affecting women of childbearing age.

According to the study results, ever use of a fungicide shows a slight increased risk (odds ratio (OR) 1.4) and ever use of an organochlorine insecticide shows a 1.2 OR for hypothyroidism. Ever use of the fungicide benomyl shows a more than tripling of risk to hypothyroidism, whereas the fungicides maneb and mancozeb show a more than doubling and the herbicide paraquat shows a nearly doubling of risk. Maneb and mancozeb also show a more than doubling of risk for hyperthyroidism, making it the only pesticide that is linked to both hyperthyroidism and hypothyroidism in the study.

The thyroid gland is a small butterfly-shaped gland inside the neck. It produces two hormones that travel through the bloodstream to all tissues of the body. Hypothyroidism occurs when the thyroid gland produces too little thyroid hormone, and hyperthyroidism refers to any condition in which the body has too much thyroid hormone. Thyroid hormone production is regulated by thyroid-stimulating hormone, which is made by the pituitary gland. Located in the brain, the pituitary gland is the “master gland” of the endocrine system.

Thyroid hormones affect metabolism, brain development, breathing, heart and nervous system functions, body temperature, muscle strength, skin dryness, menstrual cycles, weight, and cholesterol levels. The thyroid hormone is essential for normal brain development in fetuses, babies, and young children. Mild hypothyroidism in the mother is known to have harmful effects on her fetus’s brain development.

In a 2007 article, “Autism: transient in utero hypothyroxinemia related to maternal flavonoid ingestion during pregnancy and to other environmental antithyroid agents,” Gustavo C. Román, M.D., suggests that substances that interfere with thyroidal activity may produce morphological brain changes leading to autism. Scientists have identified specific changes to brain cells during development that are particular to autism, and these processes are regulated by hormones produced by the mother’s thyroid gland. Dr. Romn notes that environmental contaminants interfere with thyroid function, including 60 percent of all herbicides, in particular 2,4-D, acetochlor, aminotriazole, amitrole, bromoxynil, pendamethalin, mancozeb, and thioureas.

Triclosan, commonly found in hand soaps, toothpastes, deodorants, laundry detergents, fabric softeners, facial tissues, antiseptics, fabrics, and toys, is another pesticide that has been linked to thyroid effects. A study published in 2008 found that triclosan alters thyroid function in male rats. Other studies have found that due to its extensive use in consumer goods, triclosan and its metabolites are present in waterways, fish, human milk, serum, urine, and foods; and is linked to endocrine disruption, cancer and antibiotic resistance and found in 75% of people tested in government biomonitoring studies. A U.S Geological Survey (USGS) study found that triclosan is one of the most detected chemicals in U.S. waterways and at some of the highest concentrations. Last month, over 75 groups, led by Beyond Pesticides and Food and Water Watch, petitioned the U.S. EPA to ban non-medical uses of triclosan.

Chlorpyrifos is an organophosphate insecticide linked to many adverse effects including thyroid problems. A 2009 study, found that exposure to low levels of the chorpyrifos during pregnancy can impair learning, change brain function and alter thyroid levels of offspring into adulthood for tested mice, especially females.

Another pesticide implicated in adversely affecting the thyroid is methyl iodide, a controversial fumigant to be used primarily in strawberry fields. In EPA-reviewed lab studies, methyl iodide causes thyroid tumors, changes in thyroid hormone levels- which are closely tied to metabolic disorders, respiratory tract lesions, neurological effects, and miscarriages. Methyl iodide is a threat to air and water supplies and has been linked to very serious illnesses, including cancer, miscarriages, thyroid toxicity, and neurological problems.

According to Beyond Pesticides’ research, additional hazardous fungicides thiram, ziram and ferbam are teratogens, neuro, reproductive and thyroid toxins, mutagens, and skin sensitizers. These fungicides are used on food crops (strawberries, apples, and peaches) and for seed treatment. Prolonged occupational exposure to thiram increased the incidence of hypertension and diseases of the heart, liver, thyroid and gastrointestinal tract. Ziram causes thyroid cancer in rats and lung and lymph gland cancer in mice.

Hear more cutting edge health science at Beyond Pesticides’ 28th National Pesticide Forum, Greening the Community in Cleveland, Ohio – April 9-10, 2010. Presentations from top university researchers, including Paul Winchester, PhD; Shuk-mei Ho, PhD; Michael Skinner, PhD; and Warren Porter, PhD, will speak on pesticides and endocrine disruption, genetics, cancer, learning disabilities, and birth defects and more.