Levels of polybrominated diphenyl ethers (PBDEs) measured in human samples have increased
in recent years, but the health effects of these compounds are not well studied. A
group of persistent pollutants similar in structure to polychlorinated biphenyls (PCBs),
PBDEs are thought to affect endocrine function, but this relationship has only been
examined in several small studies. A new study significantly expands this knowledge
base by analyzing PBDE exposure among a large cohort of male sport-fish consumers
and concluding that these exposures are associated with increased thyroglobulin antibodies
and increased thyroxine (T4) in adult males independent of PCB exposure [
116:1635–1641; Turyk et al.].
The study examined 405 adult males who consumed sport fish from the Great Lakes during
the early 1990s. Researchers gathered data on the subjects’ levels of fish consumption,
medical diseases, and use of medications, and took serum samples that were tested
for PBDEs, PCBs, and DDE, a metabolite of DDT that may affect thyroid hormones. Total
and free T4 and triiodothyronine (T3) were measured in serum and urine.
PBDE concentrations were positively associated with increased T4 and reverse T3, and
inversely correlated with total T3 and thyroid-stimulating hormone (TSH). In addition,
PBDEs were positively related to the percentage of T4 bound to albumin, a carrier
protein. An observed increase in thyroglobulin antibodies in men with the highest
PBDE exposures may indicate an increased susceptibility to autoimmune thyroiditis
among people who have been exposed to PBDEs, according to the authors.
The findings of a positive association of PBDEs with T4 are not consistent with results
of animal studies that have shown decreased T4 in rats and mice exposed to PBDE. However,
the results do align with those of several smaller human studies. The authors speculate
the disparity may be attributable to the fact that, while thyroid hormone regulation
is similar among vertebrates, some functions differ by species.
A major strength of the study is the measurement of the effects of PBDEs on multiple
hormones and the consideration of other environmental exposures that can affect thyroid
hormones. The authors point out that their findings provide a rationale for future
mechanistic studies related to PBDE exposure, including how those exposures may be
linked to changes in thyroid hormone metabolism and binding of T4 to serum-binding
proteins. Also needed, they write, are larger studies to determine whether PBDE exposure
is related to thyroid disease in human populations.