Thirdhand smoke is residue that has been left on hair, skin, clothes, walls and other surfaces from tobacco smoke.
Thirdhand smoke (THS) is described as tobacco smoke chemicals that are left on hair, skin, clothes, walls, carpets and other surfaces long after a cigarette has been extinguished.
"This includes toxins that become increasingly toxic with age and are re-emitted into the air or react with other chemicals in the environment to produce new pollutants," says lead author Dr. Manuela Martins-Green, a professor of cell biology and neuroscience at the University of California-Riverside (UCR). "Some of these pollutants are carcinogenic."
It is estimated that in the US, almost 88 million non-smokers aged 3 years and older are exposed to either THS or secondhand smoke - tobacco smoke exhaled by a smoker - in their homes.
Previously, Medical News Today reported on research that linked THS to increased risk of cancer, while another study suggested exposure to THS may lead to liver, lung and skin problems.
Now, Dr. Martins-Green and colleagues suggest THS may raise type 2 diabetes risk, after they identified insulin resistance - a precursor to the condition in which cells fail to respond to the hormone insulin - in around half of mice exposed to THS.
THS exposure leads to oxidative stress, insulin resistance
To reach their findings, the researchers used a smoke machine to expose empty mouse cages to secondhand smoke, allowing the smoke to land on the surfaces and objects within the cages and become THS.
- Type 2 diabetes accounts for 90-95% of all diabetes cases
- Around 1 in 3 people will develop type 2 diabetes in their lifetime
- In 2012, around 1.7 million Americans aged 20 and older were diagnosed with type 2 diabetes.
The team then introduced mice into these cages, exposing them to the THS. The mice were fed either a standard chow or "Western diet" - representative of a high-fat diet in humans.
The effects of THS exposure were assessed and compared with control mice that were fed the same diets but that were not exposed to THS.
The team found that mice exposed to THS were significantly more likely to develop insulin resistance than the non-exposed mice, suggesting they were at greater risk for type 2 diabetes.
"In type 2 diabetes, glucose does not enter the cells, and increased levels of insulin, resulting from an overburdened pancreas, do nothing to facilitate glucose entry into cells for producing energy," says Dr. Martins-Green. "This is what we saw in 49% of the mice we exposed to THS in the lab."
This finding is down to oxidative stress - DNA damage as a result of toxins - due to exposure to chemicals in THS, according to the researchers. They found that THS exposure caused damage to proteins, fats and DNA that led to high levels of glucose in the bloodstream and insulin resistance.
The team confirmed their findings by treating THS-exposed mice with antioxidants; they found such treatment reversed the molecular damage and insulin resistance caused by THS.
Findings may have 'direct implications' for humans
Interestingly, the researchers note that mice exposed to THS that were fed the Western diet - a diet known to increase oxidative stress - showed greater levels of oxidative stress, had more severe insulin resistance and gained less weight than control mice fed the same diet.
The authors say this may explain why smokers and people exposed to secondhand smoke are more likely to lose weight. "Nicotine leads to decreased appetite but also creates accumulation of visceral fat which then leads to increased oxidative stress and eventually to the metabolic syndrome," they note.
While the study findings were observed in mice, the researchers say they may have "direct implications" for humans, who are often largely exposed to THS. They add:
"If confirmed in humans, these studies could have a major impact on how people view exposure to environmental tobacco toxins, in particular to children, elderly and workers in environments where tobacco smoke has taken place."
Dr. Martins-Green notes that she hopes the findings will encourage policy makers to launch new strategies that reduce exposure to THS toxins.
Last month, MNT reported on a study suggesting electronic cigarettes impair immune responses more than tobacco.