A home that routinely fails the “white glove test” may pose more of a health hazard than just constant sneezing. New research presented at ENDO 2019 shows that household dust could promote fat cell development in children.
There’s a saying attributed to late interior designer Mario Buatta: “Dust is a protective coating for fine furniture.” It’s a cheeky statement, to be sure, and it probably started many neat-freaks’ eyes twitching, but new evidence shows that not only is house dust unsightly, but it also appears to promote the development of fat cells, even at very limited exposure.
Christopher Kassotis, PhD, of Duke University’s Nicholas School of the Environment in Durham, N.C., and his colleagues presented their research at ENDO 2019 in New Orleans, detailing how they investigated the effects of chemicals isolated from dust samples and how they promote growth of fat cells and lipid formation.
Hundreds of chemicals have been measured in indoor house dust by several researchers, including Heather Stapleton, PhD, also of Duke’s Nicholas School of the Environment. Stapleton and her colleagues previously showed that many common indoor contaminants in dust can activate the peroxisome proliferator activated receptor gamma (PPARg), often considered the master regulator of fat cell development. “The next obvious question was whether these common contaminants (and house dust) could promote fat cell development in cell models,” Kassotis says. “My first project at Duke evaluated a suite of common indoor contaminants, finding that many of these chemicals could promote fat cell development, and that low levels of house dust extracts did as well.”
Kassotis and Stapleton, with their colleagues, next explored this association more systematically in a group of adults in a thyroid cancer cohort, evaluating the extent to which house dust extracts could promote fat cell development in a common cell model and associated this with the metabolic health of adults living in these homes. The researchers recently published their findings in Science of the Total Environment.
“We have consistently observed effects of house dust extracts at very low levels, often <10 micrograms. In comparison, children are estimated to consume between 60 and 100 milligrams of dust each day, more than 1,000 times this quantity. While these may seem like low levels, residents are often exposed to these chemicals with great frequency, contributing to nearly constant exposure.” – Christopher Kassotis, PhD, Nicholas School of the Environment, Duke University, Durham, N.C.
They found that the extent of fat cell development promoted by the dust extracts was associated with significantly greater thyroid-stimulating hormone concentrations and lower free triiodothyronine and thyroxine in adults living in those homes. The researchers further found a significant and positive association between extent of fat cell development and the body mass index (BMI) of all adults in the study. “These results highlight a contributory role of environmental [thyroid receptor] antagonism as a putative factor in metabolic health,” the authors write in their conclusion, “suggesting that further research should evaluate this mechanism and determine whether in vitro adipogenic activity could have utility as a biomarker for metabolic health in residents.”
“This suggested that exposures in the indoor environment might play a role in the metabolic health of residents, and we next wondered if this would be more pronounced in children, who may be exposed to these contaminants during a critical window of development,” Kassotis says.
Disrupting Metabolic Health
In this current study, Kassotis and his colleagues collected 194 house dust samples from households in central North Carolina, homes inhabited by families who had previously participated in a larger study, and who now had children aged about three to six years old. “Our idea was to look at children and exposure during a more critical period of development than our previous study had assessed. During gestation and early life, precise signaling and levels of hormones are critical to normal development and establishment of regulatory systems,” Kassotis says. “We hypothesized that an early exposure could potentially be more disruptive to metabolic health than an adult exposure (which we had already demonstrated).”
The study population demographics reflected those of the Durham, N.C. area – about 40% non-Hispanic white, 40% non-Hispanic black, 20% Hispanic white, and about 55% with a college degree. “Due to their previous recruitment during pregnancy for a previous study, they were perhaps more receptive to another study,” Kassotis says, “and participants were most happy about our lab members vacuuming their main living areas – a nice study perk!”
The researchers then extracted the chemicals from dust in the lab and tested their ability to promote fat cell development in a cell model. They found that about two-thirds (125 dust extracts) were able to promote fat cell development, while half (97 dust extracts) promote fat cell proliferation at just 100 micrograms. Children are estimated to ingest between 60 and 100 milligrams of dust each day, according to the Environmental Protection Agency’s Exposure Factor’s Handbook.
But Kassotis here points out that upon further analysis, he and his team did not reveal any striking impacts on child metabolic health, at least not quite the significant impacts they had previously seen on adult health.
Kassotis says that one potential factor in this weaker association may be related to the length of time people had lived in their homes. In the previous study the adults had lived in their homes for an average of nine years, in contrast to the current study with children in which some of the children had only lived in these residences for several months or years. “That said, we have consistently observed effects of house dust extracts at very low levels, often <10 micrograms. In comparison, children are estimated to consume between 60 and 100 milligrams of dust each day, more than 1000 times this quantity,” he says. “While these may seem like low levels, residents are often exposed to these chemicals with great frequency, contributing to nearly constant exposure.”
“We have measured 111 contaminants in these dust samples, but we suspect that mixture effects or as of yet undetermined chemicals are promoting most of the adipogenic activity herein. We have begun to assess that through non-target analysis, identifying chemicals present in the samples that are associated with the adipogenic activity and identifying them.” – Christopher Kassotis, PhD, Nicholas School of the Environment, Duke University, Durham, N.C.
The results of this current study so far may not have been quite what Kassotis and his colleagues hypothesized, but again, the children haven’t had quite the exposure their parents have. And the researchers found several chemicals were significantly elevated in the dust of homes of children who were overweight or obese. So the work goes on.
Kassotis and his colleagues continue to assess mechanism. He’s looking at two potential causative pathways: activation of PPARg and inhibition of thyroid receptor beta (TRb), since the previous study in adults implicated TRb’s role in some of these adverse metabolic effects. “Another path we are still evaluating is the effect of mixtures of contaminants and identifying causative chemicals,” he says. “We have measured 111 contaminants in these dust samples, but we suspect that mixture effects or as of yet undetermined chemicals are promoting most of the adipogenic activity herein. We have begun to assess that through non-target analyses, identifying mass spectral signatures present in the samples that are associated with the adipogenic activity and then trying to identify those chemicals.”
That non-target analysis has so far found about 35,000 chemicals in the dust of the homes studied, and Kassotis says he hopes this study raises awareness about the vast number of chemicals in the indoor environment. These chemicals come from myriad sources, so Buatta’s alleged comment about dust being a protective coating for furniture might not have been that far off the mark after all. But furniture obviously can’t experience adverse metabolic effects.
“There are numerous options for reducing these chemicals, from flame retardants to pesticides to plasticizers, etc.,” Kassotis says, “and I hope it will allow for more informed decisions from consumers when they make future purchasing decisions.”
— Bagley is the senior editor of Endocrine News. He wrote about the effect of some endocrine treatments on addictive behaviors in the March issue.