Your home a hotbed of thyroid?

Last Updated 21 January 2010, 16:12 IST

The substance, used to make nonstick cookware, stain-resistant furnishings and greaseproof wrappers, is believed to get into the body through contaminated food or household dust. Once in the body, it accumulates in organs and other tissues.

People with high levels of the chemical in their blood were found to be twice as likely to have thyroid problems as those with the lowest levels, according to a survey of medical records of nearly 4,000 otherwise healthy US adults. The study is published in the journal, “Environmental Health Perspectives”.

Scientists said they cannot be certain the chemical is directly responsible for the rise in thyroid disease but called for a full investigation to assess its safety.
Studies in animals have found that the chemical, PFOA (perfluorooctanoic acid), and a sister substance called PFOS (perfluorooctane sulfonate), can cause thyroid problems and a variety of other medical conditions, including hormone imbalances, liver disease and cancer.

“It’s been thought that because they’re inert they don’t cause any health problems, but we’re starting to see some evidence that is suggesting that’s not true,” said Tamara Galloway, professor of ecotoxicology at Exeter University. “Because these chemicals are inert they are persistent and they build up in the environment and also in human and animal tissues.”

We all have trace levels of PFOA in our bodies that we pick up from the environment. The substance is so stable that it persists for years. It has been detected in people around the world and in wildlife as diverse as birds, fish and polar bears.

The thyroid gland produces hormones that control the body’s metabolism and are vital for regulating heart rate and temperature. Thyroid disease can make the gland produce too much or too little hormone. An underactive thyroid can cause exhaustion, depression and weight gain. If the gland is overactive, it can cause weight loss and a rapid heartbeat. Women are 10 times more likely to have thyroid problems than men.

The Exeter researchers trawled medical records on the US National Health and Nutrition Examination Survey, a database representative of the country's adult population. They found 3,966 people aged 20 and older whose blood had been tested for PFOA and PFOS between 1999 and 2006.

The scientists put the patients into four groups depending on the concentration of PFOA in their blood. The records showed that 16 per cent of women in the top group had thyroid problems, compared with 8 per cent in the lowest group. A similar trend was seen in men, though the number who had thyroid disease was small.

The US Food and Drug Administration has a voluntary agreement with several companies to phase out PFOA production over the next few years.

The scientists, however, concede that their study does not confirm PFOA is causing thyroid disease. One alternative explanation is that thyroid disease makes PFOA accumulate more quickly in the body.

Ashley Grossman, professor of neuroendocrinology at Queen Mary, University of London, said: “We also don’t know whether this chemical is directly affecting the thyroid. Thyroid disease is often caused by the body’s own immune system attacking the thyroid gland, so perhaps this chemical is having some effect on the immune system, rather than directly on the thyroid.

“We’d need to do a lot more research to verify this link and to understand how the two are linked,” Ashley added.

Meanwhile, a spokesman for the Health Protection Agency said: “A study like this cannot establish cause and effect.”

(Published 21 January 2010, 16:02 IST)

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