Chemicals in house dust can disrupt thyroid hormone transport

A recent study led by VU-toxicologist Timo Hamers (Dept. Environment & Health) has demonstrated that chemicals in house dust can disrupt transport of thyroid hormone. For pregnant women, this can be detrimental to the brain development of the unborn child.

02/05/2020 | 2:40 PM

This study was published last week in the scientific journal Environmental Health Perspectives. House dust contains many different chemicals originating from all kinds of products that we use and wear on a daily basis. Some of these chemicals can bind to transthyretin (TTR), a protein that transports thyroid hormone in our body. Because the chemicals bind to the same binding place as thyroid hormone, less hormone is transported. As a possible consequence, less thyroid hormone reaches its target organs and unbound thyroid hormone is excreted from the body.

Decreased cognition and lower IQ
In the human body, thyroid hormone is involved in regulation of metabolism and body temperature. The researchers, however, worry most about the regulating function of thyroid hormone in early brain development. Thyroid hormone disruption during early development is associated with decreased cognition and lower IQ scores at later age.

Disruption of binding with TTR
In this new study, Timo Hamers and colleagues studied to what extent the binding of thyroid hormone to TTR is disrupted by mixtures of house dust contaminants. These mixtures reflected the composition and levels of these compounds as determined in blood of pregnant women and infants. First, they determined how well these complex mixtures bind to purified TTR under optimum laboratory conditions. Next, they extrapolated these binding properties to the actual situation in human blood, which contains not only TTR but also other thyroid hormone binding proteins.

Fetus dependent on mother for thyroid hormone
Based on their study, the researchers expect that an average exposure to chemicals present in house dust inhibits the thyroid hormone binding to TTR by a little more than 1 percent inhibition. For a high exposure, they expect about 5 percent inhibition. This level of inhibition seems low, but may contribute to reach a status of hypothyroidism, especially in people already having relatively low levels of thyroid hormone. This is especially important for pregnant women, because the fetus completely depends on the maternal supply of thyroid hormone during the first trimester of pregnancy. Thyroid hormone is important for the brain development of the fetus, and a deficiency during pregnancy may lead to decreased cognitive functions in the child after birth.