Environmental Thyroid Threats

Despite eating right and exercising regularly, Stephanie Rhodes was constantly tired and felt as if her mind were foggy. "I was sleeping a lot but not feeling rested," said the Baltimore mother of three.

The problem turned out to be an underactive thyroid gland, a surprisingly common condition that affects roughly one in 12 Americans. Controlling metabolism, energy levels, growth and prenatal development, the thyroid fails to function properly in women five to eight times more frequently than in men, often during pregnancy and menopause. Genetic factors, radiation and lack of iodine are all known to harm the butterfly-shaped organ, located at the base of the neck.

Now researchers are examining environmental chemicals in everything from hand soap to drinking water to food to determine their role in causing thyroid disorders. "We've only scratched the surface on what contaminants may affect thyroid hormone action," says Caren Helbing, Ph.D., of the department of biochemistry and microbiology at Canada's University of Victoria.

While iodine deficiency is the major cause of hypothyroidism (see "What's a Thyroid?," right), experts cannot say exactly how many cases of thyroid dysfunction can be tied to other environmental chemical exposures. It's difficult to correlate cases of disease to specific exposures because the thyroid acts on so many systems in the body. "The effects of environmental chemicals on health will probably be more visible at a population level than on an individual level because the biology of the endocrine system is so complicated," says R. Thomas Zoeller, Ph.D., chair of the department of biology at the University of Massachusetts-Amherst. That said, the prevalence of thyroid problems suggests we should avoid needless exposures to contaminants.