Second-hand smoking linked to learning disorders and ADD

by Rebecca Coxon

Every year, second-hand smoke kills around 11,000 people in the UK from lung cancer, heart disease and strokes but there is increasing evidence to suggest that it is linked to mental and neurobehavioural disorders too and could increase the risk by up to 50%.

Researchers from the Harvard School of Public Health found that children who were exposed to second-hand smoke were twice as likely to develop so-called neurobehavioral disorders -- including learning disabilities, ADD or ADHD, and conduct mental or behaviour disorders -- than were children who lived in smoke-free homes.

The research looked at the data generated by a 2007 national health survey, analyzing the responses of the parents of guardians of more than 55,000 children ages 11 and younger from throughout the U.S.

"We estimate that 274,000 cases of the most common neurobehavioral disorders could have been prevented with smoke-free homes," said Hillel Alpert, ScM, a senior research associate at Harvard and one of the study's authors.

Strong evidence

While the study did not find that second-hand smoke directly caused any of these mental health issues, Alpert argues that the "strong evidence of association" between second-hand smoke exposure and the incidence of certain disorders might underline a causal relationship that could be discovered with future long term investigations.

Over forty percent of children in the UK live in a household where at least one person smokes, and a study by the Royal College of Physicians showed that about 17,000 children in the UK are admitted to hospital every year because of illnesses caused by second-hand smoke.

Growing research

In the past few years there have been a growing amount of studies and research focused on the link between second-hand smoke and mental health problems:

An August 2010 study in the Archives of General Psychiatry, which analysed results from the Scottish Health Survey, found that people exposed to second-hand smoke were more likely to suffer from psychological distress.

Similarly, a 2008 study in rats that found that nicotine exposure during adolescence led to a "depression-like state" and increased sensitivity to stress and anxiety in those animals.

Another new study, also published this week in Pediatrics, suggests that children who are exposed to second-hand smoke are more likely to become smokers themselves.

More toxic: Sidestream smoke

Second-hand smoke consists mainly of sidestream smoke, which is about four times more toxic than mainstream smoke, although people inhale it in a more diluted form, according to Cancer Research UK. Shockingly, sidestream smoke contains much higher levels of many of the poisons and cancer-causing chemicals in cigarettes, which explains why the risks from second-hand smoking are so vast and should be taken on board by all smokers, particularly those with children. Sidestream smoke contains: