Stain repellents affect thyroid hormone levels in adult Inuits.
Dallaire, R, É Dewailly, D Pereg, S Dery and P Ayotte. 2009. Environmental exposure to common compounds impacts thyroid function. Environmental Health Perspectives DOI:10.1289/ehp.0900633.
Several long-lived pollutants measured in the blood of Canadian Inuits are associated with altered thyroid hormone levels, this study finds. It is unclear, though, whether the exposures are associated with ill health effects.
The study highlights again how long-persisting environmental pollutants – classified as polyhalogenated compounds – can accumulate in people and alter normal hormone levels. It is unique because it included women and is one of the first large-scale studies to look at the stain repellent PFOS's effects on thyroid hormone.
Adult health depends on thyroid hormones. The suite of hormones help maintain a normal heart rate; regulate body temperature; and support other body functions, including metabolism, mental health, reproduction and digestion. Too much or too little of the hormones can lead to health problems.
Native Inuit people have a high risk of exposure to many harmful pollutants because of their traditional diets. A mainstay is seafood – especially fish and marine mammals – that can contain PCBs, organochlorines and other persistent chemicals.
The polyhalogenated compounds are not easily broken down in the environment by sunlight or chemical and biological decomposition. The compounds can also travel long distances on wind currents, ending up in remote locations far from their sources. As a result, they tend to accumulate in animals and concentrate in their tissues as they move up the food chain.
The researchers measured numerous currently used and banned chemicals in the blood of adult Inuits and compared them to markers of thyroid hormone function. They also administered questionaires and conducted interviews with the participants. This cross-sectional study gives a snapshot of the population at one point in time.
The study occurred between August and October in 2004 and included 1,056 permanent residents of Nunavik (Québec, Canada). The authors measured PCBs and their metabolites, organochlorine pesticides, halogenated phenolic compounds, PBDEs, PFOS, and dioxin-like compounds. Thyroid hormone function was evaluated by measuring serum thyroid-stimulating hormone (TSH), thyroxin, T3 and thyroid-binding globulin (TBG).
Higher PFOS exposures were associated with reduced thyroid hormone measures of TSH, T3 and TBG levels and higher thyroxine levels. Both low TSH and elevated thyroxine are associated with hyperthyroidism, a condition in which too much thyroid hormone is produced.
This study associated trends in thyroid hormone level with exposure to polyhalogenated compounds. Further research is needed to discern if these associations lead to increased thyroid disease.
