As if we needed another reason to cut carbon emissions, a new study has found that rats exposed to Beijing’s smog-laden air develop metabolic problems and gain more weight than their peers, possibly adding another facet to the ever-complex global obesity epidemic.
“We used to think that air pollution just affected our lungs,” study author Junfeng Zhang told IFLScience. “It's only been in the last 10 years that we found it also affects our heart. Now we know it affects everything, including our metabolism and bodyweight.”
This isn’t actually the first time that links have been drawn between dirty air and weight problems. Previous work in Southern California found that people living in areas with the most traffic, and therefore likely air pollution, tended to have a higher body mass index. A study in New York City also found an association between exposure to certain air pollution particles during pregnancy and childhood obesity.
In addition to this observational research, some experimental work in rodents has found similar trends, although studies either only looked at diet-induced weight gain or used protocols that weren’t representative of real-life air pollution exposure.
To fill this gap, a team from Duke University turned to the choking air of Beijing. Since the concentrations of pollution particles have been so bad here in recent years that they’re comparable to artificial exposure chambers, all the team needed to do was place rodents in a chamber with air coming directly from outside. They also had a control group that was placed side-by-side in a different chamber that was fitted with a highly efficient air filter.
All of the rats were pregnant and maintained on the same normal diet, and when they produced pups these were kept in the same conditions as their mothers – either dirty air or filtered air – until they were analyzed at either three or eight weeks of age.
Even though the two groups were fed the same food, those exposed to air pollution weighed more at the end of the study. ARTSILENSE/Shutterstock
Described in the Journal of the Federation of American Societies for Experimental Biology, after just 19 days those exposed to unfiltered air showed a number of telltale signs of disrupted metabolism, including increased resistance to insulin – a precursor of Type 2 diabetes, worse fat profiles, higher “bad” cholesterol levels, and heavier livers. All the rats were roughly the same weight at the start, but those breathing in the smoggy air weighed significantly more at the end of their pregnancies.
"If our metabolic function becomes impaired, then we are less capable of converting fat and sugar into energy," said Zhang. "This is what we saw in the rats that were breathing in the dirty air."
Perhaps most notably, when the team examined the rats' tissues, they saw markers of inflammation, not just in the lungs but in other tissues too. "Chronic inflammation is a very common pathway for almost every disease, and we know it increases the risk for obesity," added Zhang. "So the mechanism is quite clear."
In addition, the resulting pups also showed similar problems, with the pollution-exposed offspring gaining much more weight than their unexposed peers. However, the effects were only apparent when examined at eight-weeks old, indicating that metabolic problems arise as a result of long-term, rather than short-term, pollution exposure.
As chronic inflammation can result in the production of damaging molecules that can mess up metabolic reactions, the researchers propose a scenario whereby continuous exposure to irritating air pollutants triggers tissue stress in the lungs that can then spill over into the rest of the body, ultimately leading to metabolic dysfunction and a greater risk for obesity. Although further studies are needed to verify this in people, we already know that breathing in air pollution causes health problems that can bring an early grave, so we shouldn’t need an extra excuse to act.