Could the Dust in Your House Make You Gain Weight?
While scientists agree that diet and exercise are the most important factors in weight gain, some wonder if the chemicals we are exposed to in our daily lives—such as those found in household dust—could contribute to weight gain.
Duke University professor Heather Stapleton and her co-authors examined a mixture of chemicals extracted from household dust to understand whether they could influence the growth and development of fat cells. To understand why they suspected household dust as a potential cause of weight gain, let's take a step back and look at Stapleton's earlier research on flame retardants.
Until a little over a decade ago, a group of chemicals called PBDEs (polybrominated diphenyl ethers) were commonly used flame retardants in household products. When they were found harmful and then internationally banned and phased out under the Stockholm Convention on Persistent Organic Pollutants, manufacturers turned to other flame retardants instead.
The question now was, which chemicals were they using? Are humans being exposed to the new chemicals? And if so, are they harmful? That's what Stapleton’s research team wants to know.
In 2015, she and coauthors Kate Hoffman, Stavros Garantziotis and Linda S. Birnbaum published a paper titled, "Monitoring Indoor Exposure to Organophosphate Flame Retardants: Hand Wipes and House Dust." The term "organophosphate" refers to molecules that include both carbon and phosphorus. Organophosphates are a large group of chemicals with multiple uses. Some are used as plasticizers (used to soften plastics), others are used as pesticides, and some are now used as flame retardants. One of them, called chlorinated tris or TDCPP for short (its full name is tris[1,3-dichloroisopropyl] phosphate), may cause cancer.
In that study, the scientists found the organophosphate flame retardants they were looking for—including carcinogenic chlorinated tris—in most samples of household dust tested, and on study participants’ hands. They also found metabolites of these chemicals in study participants' urine. What was not certain was whether exposure to the chemicals was due to household dust. It seems likely that study participants got the chemicals on their hands and then either absorbed them through their skin, inhaled them, or ingested them through hand to mouth contact.
Nonetheless, household dust was implicated. And dust did not just contain one potentially harmful chemical. It contained many. Yet often scientists only examine the effects of one chemical at a time. Stapleton and her colleagues decided to change that. "We're so busy looking at one chemical at a time," she said. "It's important we start looking at these mixtures we're exposed to."
A second study she coauthored in 2015 began to look at the link between chemical exposures and regulation of nuclear receptors, or proteins in our cell that help regulate development and metabolism. Scientists knew that exposure to some chemicals in the weeks before and after birth can cause animals to gain weight, and sometimes become obese, and they suspected that others, like flame retardants, might do so as well. These are chemicals that come into homes on commercial products and migrate into household dust. Since the EPA estimates children ingest 50mg of dust per day, it's important to find out whether all the chemicals we’re exposed to from dust are harmful.
This second study tested individual chemicals as well as 24 household dust samples to see if they bound to receptors inside cells that are known to increase production of adipocytes, or fat cells. Many of the chemicals, and 21 of the 24 dust samples, did bind to the receptor to some degree—but that alone was not enough to know if the chemicals actually did cause the adipocytes to grow and produce lipid.
Her new study, coauthored with Kate Hoffman and Christopher D. Kassotis and published in the journal Environmental Science and Technology, takes the research to the next step. This time, the researchers exposed mouse cells to 41 different chemicals and 11 household dust extracts. The chemicals tested included common flame retardants, pesticides, phthalates, and parabens (chemicals often used as preservatives in cosmetics). All in all, 28 of the chemicals tested and nearly all (10 out of 11) dust extracts caused the cells to either proliferate or generate more lipid.
It's true that we do not intentionally eat dust, but we sometimes inhale it, or it can get on our hands and then into our mouths. One of the most alarming facets of the study is that the doses needed to have an effect on the mouse cells was tiny—far less than the amount the EPA estimates children are exposed to. The next step after this to see if exposure to mixtures present in household dust, or any of the 41 chemicals tested, leads to significant weight gain in live animals.
With the carefulness of a scientist, Stapleton cautions we need research before jumping to conclusions. Even if we ingest a chemical, that does not mean the chemical stays in our body. We might excrete it—or metabolize it so it becomes a different chemical. Furthermore, she adds, the estimate that children consume 50mg of dust per day is just an estimate.
Another question she'd like to study is whether the impact these chemicals have on a person depends on stage of life. It's possible that a chemical that has no effect on a grown man will have an enormous impact on someone exposed as a child or in utero.
For those of us who are exposed to these chemicals day after day in our own homes, the question is not just whether they make us gain weight more easily. That is just one impact out of many that the mixture of chemicals we live with may have on us, as many of these chemicals have previously been associated with increased risks for cancer, infertility/subfertility, adverse pregnancy outcomes, developmental abnormalities, and other adverse health outcomes. The question we must ask is whether living in a potentially toxic soup as we wait for definitive proof of harm from scientists is worthwhile, or if the benefits we gain from using these chemicals are not worth the risk.