Commentary: Second-hand smoke could cause mental health problems in young and old, especially

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Breathing in second-hand tobacco smoke increases your risk of lung cancer and many other diseases. But a growing body of research suggests it can also affect your mental health.

More than 70 studies from many countries have found that people exposed to second-hand smoke are more likely to suffer from depression, anxiety, stress, attention deficit hyperactivity disorder (ADHD) and dementia, especially if the exposure is important.

Numerous studies have linked second-hand smoke exposure to depression, with higher exposures being associated with more severe depressive symptoms.

A survey of more than 21,000 children aged 6 to 11 in the United States last year found that those exposed to high levels of second-hand smoke were 80% more likely to have been diagnosed with an anxiety disorder.

Among young people, exposure to second-hand smoke is also linked to a higher risk of suicide. Students in Canada, Korea and Taiwan who were exposed to high levels were between 78% and three times more likely to have attempted or thought about suicide.

It is also linked to learning difficulties, behavioral problems and ADHD in children.

The same 2021 US survey found that children exposed to second-hand smoke at home were 65% more likely to have ADHD and about twice as likely to have behavioral problems or developmental delays.

In adults, exposure to second-hand smoke is also linked to a higher risk of dementia.

A Chinese study followed women for two years and found that the longer they were exposed to second-hand smoke, the more their memories declined over the two years, putting them at increased risk for dementia.

Similarly, other studies have found that people with high lifetime exposure to second-hand smoke were two to three times more likely to be diagnosed with dementia or Alzheimer’s disease.

SECOND-HAND SMOKE AT HOME

Second-hand smoke is hard to avoid in some places, like the home. Home is also a place where we seek a sense of security and refuge.

It’s hard to do when you’re constantly having to breathe in someone else’s toxic smoke.

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

Some study participants lived with a smoking family member, while others lived in non-smoking homes that were affected by second-hand smoke from neighbors.

Participants described second-hand smoke from neighbors as a significant source of stress, anxiety, and negative mood. Although they wanted to enjoy a smoke-free home, they couldn’t.

This caused them to feel frustrated, hopeless, worried about the health effects and unable to sleep whenever smoke seeped in through the bedroom window. This was especially the case for parents who were concerned about the health of their children.

As one participant said, “You feel like you’re choking on smoke, then you keep thinking about the health effects you might be experiencing.

In cases where second-hand smoke comes from a family member, it could compromise family relationships which, in turn, could affect mental well-being.

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 worry about me, a non-smoker, inhaling it all. It also led to conflicts or non-smoking family members hiding in their rooms to avoid the smoke.

CHICKEN OR EGG?

Most studies of the link between second-hand smoke and mental health have measured associations at some point in time.

As such, it is not possible to tell whether second-hand smoke causes mental health issues or is instead a sign of being in an environment that contributes to poor mental health.

For example, smoking tends to be more common among low-income people. As such, living with a smoker may reflect living in a family environment affected by financial stress which, in turn, affects mental health.

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

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

Specifically, secondhand smoke activates nicotine receptors in the brain, which can disrupt brain pathways involved in attention, memory, and mood via 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.

During pregnancy, second-hand smoke restricts the flow of oxygen to the fetus, which can affect brain development.

Although this effect is more pronounced if the mother smokes, it is also seen in children of non-smoking mothers who were exposed to second-hand smoke from other people during pregnancy.

A MORE NUANCED UNDERSTANDING

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

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

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

Because the research is relatively new, with most studies having been published within the last fifteen years, health researchers are still figuring out how and to what extent second-hand smoke contributes to mental health disorders.

However, if this burgeoning body of research has any message, it is that the potential mental health effects of second-hand 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 conducts research to support tobacco control policies in Singapore.

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