Commentary: Secondhand smoke could cause mental health issues for young and old especially

Breathing in secondhand tobacco smoke increases your risk of lung cancer and many other diseases. But there is growing research that suggests it may affect your mental health as well.

Over 70 studies from numerous countries have found that people exposed to secondhand smoke are more likely to be suffering from depression, anxiety, stress, Attention Deficit Hyperactivity Disorder (ADHD) and dementia, especially if exposure is heavy.

Numerous studies have linked secondhand smoke exposure to depression, with higher exposures associated with more severe depressive symptoms.

A survey of over 21,000 children aged 6-11 years old in the United States last year found that those exposed to high levels of secondhand smoke were 80 per cent more likely to have been diagnosed with an anxiety disorder.

In young people, secondhand smoke exposure is also linked to a higher suicide risk. Students in Canada, Korea and Taiwan who were exposed to high levels were between 78 per cent and three times more likely to have attempted or thought about committing suicide.

It is also linked to learning difficulties, behavioural issues, and ADHD in children.

The same 2021 US survey found that children exposed to secondhand smoke at home were 65 per cent more likely to have ADHD and roughly twice as likely to have behavioural issues or developmental delays.

In adults, secondhand smoke exposure is also linked to a higher dementia risk.

A Chinese study followed women over two years and found that, the longer they had been exposed to secondhand smoke, the more their memories had declined over the two years, putting them at a higher risk of dementia.

Other studies, similarly, found that people who were heavily exposed to secondhand smoke over their life-course were two to three times more likely to be diagnosed with dementia or Alzheimer’s disease.

SECONDHAND SMOKE AT HOME

Secondhand smoke is hard to avoid in certain places, such as the home. The home is also a place where we seek a sense of safety and sanctuary.

That is difficult to do when you are constantly forced to breathe in someone else’s toxic smoke.

A recent Singapore study, published in the journal BMC Public Health, explored the mental health impacts of in-home secondhand smoke exposure.

Some study participants were living with a smoking family member, while others were living in non-smoking homes that were affected by secondhand smoke from neighbours.

Participants described secondhand smoke from neighbours as a significant source of stress, anxiety, and negative moods. Although they wanted to enjoy a smoke-free home, they were unable to.

This led to them feeling frustrated, hopeless, anxious about the health effects, and unable to sleep whenever smoke crept in through the bedroom window. This was especially the case for parents who worried about the health of their children.

As one participant put it: “It feels like you’re being suffocated by the smoke, then you keep thinking about the health effects that you might be experiencing.”

In cases where the secondhand smoke is from a family member, it could compromise family relationships which, in turn, may affect mental wellbeing.

In the Singapore study, participants felt frustrated, disappointed, and resentful when a smoking family member was reluctant to smoke outside the home.

As one spouse described it: “[they] don’t care about me, a non-smoker, inhaling all this.” It also led to conflicts or non-smoking family members hiding in their room to avoid the smoke.

CHICKEN OR EGG?

Most studies on the link between secondhand smoke and mental health measured the associations at a single time-point.

As such, it’s not possible to tell whether secondhand smoke causes mental health issues, or is more a sign of being in an environment that contributes to poor mental health.

For example, smoking tends to be more common in people on a low income. As such, living with a smoker may be a reflection of living in a home environment impacted by financial stress which, in turn, affects mental health.

However, biomedical studies suggest that there are mechanisms by which secondhand smoke directly affects mental health.

Secondhand smoke contains neurotoxins such as nicotine, lead and carbon monoxide. These neurotoxins are especially dangerous to young children, as their brains are still developing.

Specifically, secondhand smoke activates nicotine receptors in the brain which can mess with brain pathways involved in attention, memory and mood through the dopamine and serotonin networks.

Imbalances in these pathways have been linked to a wide range of mental health disorders including depression, anxiety, ADHD and dementia.

In pregnancy, secondhand smoke constricts the oxygen flow to the foetus which can affect brain development.

Although this effect is most pronounced if the mother smokes, it’s also observed in the children of non-smoking mothers who were exposed to other people’s secondhand smoke during their pregnancies.

A MORE NUANCED UNDERSTANDING

Given the many serious health effects, people are right to feel anxious about breathing in secondhand smoke.

It is a toxic mix of over 7,000 chemicals and a well-established cause of lung cancer, heart disease, respiratory diseases, cot death in children and a wide range of other diseases, based on a substantial body of research dating back over four decades.

But its impact on mental health is likely to be more complex.

As the research is relatively new, with most studies published in the past fifteen years, health researchers are still in the process of understanding how, and to what extent, secondhand smoke contributes to mental health disorders.

However, if this nascent body of research does have one message, it is that the potential mental health impacts of secondhand smoke should not be overlooked.

ABOUT THE AUTHOR

Dr Yvette van der Eijk is an Assistant Professor at the NUS Saw Swee Hock School of Public Health. She leads research to support tobacco policies in Singapore.