Fluorochemicals thyroid disease link
Chemistry & Industry - 8 February 2010
A chemical used in non-stick cookware and water resistant coatings for carpets and fabrics has been linked to diseases of the thyroid by a large retrospective epidemiological study. Higher levels of perfluorooctanoic acid (PFOA) and other perfluoroalkyl acid (PFAA) chemicals in the blood were discovered to be associated with a higher risk of conditions, such as hypothyroidism. Researchers at the University of Exeter, UK, and the Peninsula Medical School in the US, analysed the US government’s National Health and Nutrition Examination Survey (NHANES), which took blood samples from 3966 people and checked their PFOA and PFAA levels between 1999 and 2006. The researchers found that the 25% of people with the highest levels of PFOAs in their blood – more than 5.7ng/ml – were twice as likely to report a thyroid condition than the half of the cohort that had the lowest levels – <4ng/ml. Similar links between another fluorochemical, perfluorooctane sulfonate (PFOS), and thyroid disease were uncovered in men, but not in women (Environmental Health Perspectives doi:10.1289/ehp.0901584).
‘Higher concentrations of serum PFOA and PFOS are associated with current thyroid disease in the US general adult population,’ says author Tamara Galloway from the University of Exeter. However, she adds, ‘We cannot be sure from this study that PFOA/S is directly causing thyroid disease.’ Other possible explanations for this correlation, Galloway says, might be that thyroid disease alters how PFOA/S is processed in the body or that PFOA/S is a marker of some other factor linked to thyroid disease. Diane Benford, head of toxicology of food at the UK Food Standards Agency, says: ‘This type of study investigates associations and cannot establish causality. It is important to look at the consistency of the data with the results of other studies, and with what is known about the toxicity of PFOA and PFOS, which differ.’
Ieuan Hughes, head of the department of paediatrics at the University of Cambridge, UK, says: ‘The authors recognise the blindingly obvious… that more work needs to be done to prove any association.’ He says that this, at a minimum, would mean looking at thyroid hormone levels in tandem with PFOA/S exposure. Galloway says that work to clarify the mechanism of association is ‘urgently needed’ and points out that a large study is underway in the US examining 60,000 people who were exposed to much higher PFOA levels than the general population. This population suffered higher than usual exposure due to working at, or living near, DuPont’s Washington Works in West Virginia, US, which produced fluorochemicals.
There are over 8000 perfluorinated compounds manufactured today...
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