Mice given third degree

Mice exposed to household fabrics contaminated with ‘third-hand’ tobacco smoke showed changes in biological markers of health after only one month, according to a story in The Conversation (Australia) citing a recent study. After six months, the mice showed evidence of liver damage and insulin resistance, symptoms that usually precede the development of type 2 diabetes.

The story described third-hand smoke as the residue left behind after cigarettes are smoked. ‘Once the smoke clears, after a cigarette has been extinguished, nicotine and other harmful chemicals left behind can stick to surfaces and fabrics,’ the story said. ‘This residue is known as third-hand smoke.’

The Conversation said that the idea of third-hand smoke had been around for a few decades, but that it had come to prominence in 2009 after a study by Jonathan Winickoff, an assistant professor of paediatrics at Harvard Medical School, had identified a link between parents’ belief that third-hand smoke might cause harm and the likelihood they would prohibit smoking within their homes.

‘The new mouse model study investigated the effects of third-hand smoke exposure over time on animal health (the first study to do so),’ the story said. ‘The researchers, from the University of California, Riverside, used a smoking machine to create third-hand-smoke-contaminated household fabrics in mice cages, including curtain material, upholstery and carpet. Once the fabrics showed levels likely to be found in smokers’ homes, the mice were placed in the cage and monitored over a period of six months.

‘After just one month, the mice showed changes in markers of health in the blood serum, liver and brain tissues. The range and severity of the changes on the health of mice got progressively worse the longer they were exposed.

‘After four months, the mice showed increases in factors related to oxidative stress and liver damage. Fasting glucose and insulin levels increased with third-hand smoke exposure and, after four months, the mice already had a[n] increased risk of type 2 diabetes.

‘The speed at which third-hand smoke residues cause measurable health effects in the mice is surprising. How the health effects observed in mice translate to humans, though, remains an open question.’