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BPA, Phthalates Linked to Thyroid Hormone Levels


Plastics have infiltrated many areas of our lives, and some of those ways are proving to be unhealthy. A new study finds that chemicals in plastics, namely phthalates and bisphenol A (BPA), have a negative impact on thyroid hormone levels in humans.

BPA and phthalates pose many hazards

One does not have to look far to see the numerous studies published in recent years on the potential health hazards associated with BPA and phthalates. Now investigators at the University of Michigan (UM) have added more disturbing findings about the chemicals.

Using data from the United States National Health and Nutrition Examination Survey from 1,346 adults and 329 adolescents, the researchers compared urine metabolites and serum thyroid hormone levels for these substances. Overall, they found the greater the concentrations of urinary phthalate metabolites and BPA, the more the serum levels of certain thyroid hormones decreased.

Thyroid hormones have an impact on nearly every tissue in the body. In addition to its major role in metabolism, thyroid hormones are involved in brain development, heart rate, lung function, blood function, bone growth, steroid hormone production, and some immune system processes.

The investigators studied several phthalates, including DEHP and DBP, which are used as plasticizers (substances that increase flexibility in plastics). Plasticizers tend to leech out of plastics over time, contaminating whatever they touch (e.g., food, beverages).

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DEHP, to which people are exposed to mostly through food, showed the strongest impact on thyroid hormones, specifically total thyroxine (T4), free T4, total triiodothyronine (T3), and thyroglobulin. Urine samples in the highest 20 percent of exposure to DEHP showed as much as a 10 percent decrease in some thyroid hormones when compared to urine samples at the lowest 20 percent of exposure.

The investigators also saw “suggestive inverse relationships” between urinary BPA and thyroid stimulating hormone and T4. No significant relationship was found between thyroid measures and exposure to DBP.

Previous studies have shown BPA, an industrial chemical used primarily in plastics and food packaging (especially the lining of cans), to be associated with heart disease, male sexual dysfunction, hyperactivity in children, and asthma.

Similarly, health issues such as ADHD, behavior problems in children, and reproductive difficulties have been associated with phthalates, another industrial chemical used in plastics and in health and beauty products, and found in food from the manufacturing process.

The authors of the study concluded that “these results support previous reports of associations between phthalates, and possibly BPA, and altered thyroid hormones.” Lead author John Meeker, assistant professor at UM, noted that although this study focused mainly in adults, it highlights the need for more research on pregnant women and children, as fetal and child development may be especially susceptible to thyroid hormone disruptions.

Meeker JD, Ferguson KK. Environmental Health Perspectives 2011; online 2011 July 11; doi: 10.1289/ehp.1103582
University of Michigan

Updated 4/19/2016