People with higher residues in their blood of a chemical used to make non-stick coatings for frying pans and water-repellent clothing have a far greater likelihood of reporting thyroid diseases, according to a new study released Thursday.
The finding is the first time exposure to the chemical, known as perfluorooctanoic acid or PFOA, has been linked to thyroid-related illness, one of the most common medical problems experienced by women in North America. Thyroid disorders are estimated to affect one Canadian out of 20, and are five to seven times more common in women, according to the Thyroid Foundation of Canada.
The study, published in the peer-reviewed journal Environmental Health Perspectives, found that in a group of nearly 4,000 people in the United States, those with elevated PFOA levels were more than twice as likely to report being on medication to treat thyroid conditions as those with lower concentrations of the chemical.
Almost everyone carries detectible blood levels of PFOA, a nearly indestructible chemical used to make many consumer products. Besides cookware, it is used to make grease- and stain-resistant fast food containers and carpets, among other uses.
In 2006, because of concerns over possible health effects of the chemical, U.S. and Canadian regulators asked manufacturers to reduce emissions and product content of PFOA by 95 per cent by 2010 - and virtually eliminate it by 2015. While manufacturers say little or no PFOA is left in consumer products after manufacture, environmentalists argue that non-stick coatings can break down into PFOA, which can be absorbed by animals and people.
Previous surveys of people haven't found a link to thyroid disease, although animal research has linked chemicals belonging to the same family of substances as PFOA to thyroid hormone imbalances, cancer and altered fetal development.
"These results highlight a real need for further research into the human health effects of low-level exposures to environmental chemicals like PFOA that are ubiquitous in the environment and in people's homes," commented Tamara Galloway, professor of ecotoxicology at the University of Exeter in the U.K. and the lead author.
The study was based on data compiled by the U.S. Centers for Disease Control. The U.S. government agency tested about 4,000 adults for their PFOA levels from 1999 to 2006, and took extensive histories of their medical conditions. More than 16 per cent of women and 3 per cent of men reported thyroid problems, while nearly 10 per cent of women and nearly 2 per cent of men reported being on medication to treat a thyroid condition.
Those surveyed were divided into four groups, based on the amount of PFOA in their blood. The 25 per cent with the highest levels of the chemical had more than twice the reported rate of thyroid problems as the 50 per cent with the least.
Once people ingest a quantity of PFOA, it takes about four years for half of the chemical to be cleared from the body by the kidneys.
Thyroid hormones are some of the body's most important chemical messengers, telling cells how much energy to use. They help regulate such processes as body temperature and heart rate. People whose thyroid isn't active enough, one of the most common medical conditions, have a tendency to gain weight and feel fatigued.
While the study found an association between high PFOA levels and reported thyroid conditions, one of the other researchers involved cautioned that the finding doesn't prove chemical exposures caused illnesses. Some other unknown factor could be at work, or having thyroid problems might lead to people to have increased levels of the chemical.
"We can't be sure whether it's a causal effect," said David Melzer, an epidemiologist at the U.K.'s Peninsula Medical School.
Roger Goodman, spokesman for a major manufacturer of non-stick chemicals, DuPont, says surveys of workers who are exposed to far higher amounts of it haven't found thyroid effects. He said the company has cut emissions of PFOA at its manufacturing sites by 98 per cent.