New Research Links Smoking to Greatly Increased Risk of Mental Illness

Cigarette Smoke

A new study indicates a link between smoking and an increased risk of mental illness. Utilizing data from the UK Biobank, the research suggests smoking may contribute to depression and bipolar disorder, with genetic factors playing a significant role. The findings imply a potential impact of nicotine on mental health and raise considerations for policy changes in cigarette sales.

New figures from the Technical Sciences department at Aarhus University indicates a connection between smoking and an increased likelihood of hospitalization due to mental illness in later stages of life.

Most of us know that smoking is unhealthy. Cigarette packets bear graphic warnings of physical side effects like diseased lungs and rotting teeth, and the media often reports on the association between smoking and various cancers.

However, you might not know that smoking may also increase your risk of developing mental illnesses.

In recent years, more research has indicated a strong correlation between smoking and mental illness. However, researchers have not been able to agree on whether smoking causes depression or other mental disorders, or whether we smoke because we need to lessen the symptoms of a latent mental disorder.

New figures from Aarhus University hint at the possibility that smoking can lead to mental illness.

Together with two colleagues from Canada, Doug Speed from the Center for Quantitative Genetics and Genomics at Aarhus University has shown that smoking can probably lead to depression and bipolar disorder.

“The figures in our study show that smoking might increase the risk of being hospitalized with a mental illness. It does not mean, however, that smoking is the only cause, but it does look like smoking increases that risk by 250 percent”, he says.

Based on health data from 350,000 people

For Doug Speed and his colleagues to be able to answer whether smoking can cause mental disorders, they needed very large volumes of data. There can be many different reasons why we develop a mental disorder. It was therefore important that they had enough data to clean their figures from other possible effects.

They gained access to the UK Biobank, one of the largest databases in the world of human health information. The database contains genetic data on more than half a million people. The genetic data was paired with a lot of other health information and answers provided by the participants regarding their lifestyle.

They fed the data into a computer and began looking for patterns. Doug Speed and his colleagues are far from the first researchers to investigate this correlation, but they found a new way to do it, as he explains.

“Previous research hasn’t really considered that there may be a temporal dimension at play. People typically start to smoke before the age of 20, but aren’t admitted to hospital with a mental disorder until they’re between 30 and 60 on average.” 

“Smoking typically comes before the mental illness. In fact, a long time before. On average, people from the data set began smoking at the age of 17, while they were typically not admitted to hospital with a mental disorder until after the age of 30.”

Your genes affect whether you become a smoker

As many as 90 percent of the people in the data set who were still smokers or former smokers started before the age of 20. The likelihood that you will start smoking later in life is therefore quite small. In fact, your genes help determine whether or not you will become a smoker, explains Doug Speed.

“When we looked at the many smokers in the database, we found a number of recurring genetic variants. By looking at twin studies, in which the twins had the same genes but grew up in separate homes, we could see that their genes could explain 43 percent of the risk of becoming a smoker.”

In the homes where the adoptive parents also smoked, the risk of the child starting to smoke increased. However, if the parents didn’t smoke, the risk was lower, but still greater when the children’s ‘real’ parents had been smokers and passed on certain genes.

“There are a number of genetic variants that we can refer to as ‘smoking-related genes’. The people in the data set who carried the smoking-related genes but did not smoke were less likely to develop mental disorders compared to those who carried the genes and smoked,” he says and continues:

“Because the genetic variants also seem to be linked with the risk of mental illness, this used to be a bit blurry. But in this study, we demonstrate that it’s probable that the risk of starting to smoke causes the risk of developing mental disorders to increase due to the ‘smoking-related genes’”.

Nicotine may damage the brain

Statistically, smoking probably causes mental disorders such as depression, bipolar disorder, and schizophrenia. A causal relationship has not been proven, but there is a strong correlation. It means, translated into everyday language, that there is a connection between smoking and mental illness, but the direction of the causal effect is not yet completely proven.

However, Doug Speed and his colleagues have no explanation as to why smoking might lead to mental illness. Only a number of theories.

“We still need to find the biological mechanism that causes smoking to induce mental disorders. One theory is that nicotine inhibits absorption of the neurotransmitter serotonin in the brain, and we know that people with depression don’t produce enough serotonin,” he says.

When you smoke a single cigarette, nicotine activates the production of serotonin in the brain. Among other things, this is what makes you feel relaxed after smoking. But if you continue to smoke, nicotine will have the opposite effect. Instead, it will inhibit the serotonin – which can make you anxious, upset, and unstable.

“Another explanation could be that smoking causes inflammation in the brain, which in the long term can damage parts of the brain and lead to various mental disorders. But as I said: We don’t know for sure as yet,” he says.

Should we raise the age limit for buying cigarettes?

One of the things the new figures show is that we rarely start smoking after the age of 20. Therefore, it might be a good idea to look into whether we should raise the age limit for buying cigarettes.

“This could be a good way to prevent people from starting smoking. Again, we don’t know why people don’t start smoking after the age of 20, but perhaps it’s because we become less and less willing to take risks with age,” says Doug Speed, and continues:

“Changing the law and raising the age limit may therefore have an effect. At least there are indications for this.”

The figures on which the study is based are from the UK. So they are not based on Danes. However, Doug Speed believes that the differences, if any, are very small.

“Denmark and the UK are very similar, and I would say that they are quite comparable. Having said that, our next step is actually to conduct the same study with figures from Denmark and Finland. However, getting access to this data is more expensive, which is why we did a pilot study with the British data to see if there was a correlation,” he concludes.

Reference: “Using polygenic risk scores to investigate the evolution of smoking and mental health outcomes in UK biobank participants” by Lloyd Balbuena, Evyn Peters and Doug Speed, 21 August 2023, Acta Psychiatrica Scandinavica.
DOI: 10.1111/acps.13601

4 Comments on "New Research Links Smoking to Greatly Increased Risk of Mental Illness"

  1. “Again, we don’t know why people don’t start smoking after the age of 20, but perhaps it’s because we become less and less willing to take risks with age,” says Doug Speed”
    Nope. I was born in the 1950’s and grew up in 1960/70’s, the age of unlimited smoking virtually everywhere, in offices, in cars, on public transportation, in restaurants, even in some movie theaters.

    Kids smoked because of two reasons. One, it was something that many adults did (often their parents and family members) and kids always want to act/look older than their years. Smoking made them think they were more mature. And two, smoking is sexy when you are young. There are plenty of smoking fetish sites on the web, especially featuring woman 18-25.

    Each group (smokers vs. non-smokers) tend to hang out separately. By age 20-21, you’ve bonded with your group. If you are in the non-smoking group, then you’ll tend to stay that way. If you are in the smoking group, then you are already a smoker.

    Smoking loses its sexiness after you have been smoking for 15-20+ years and the effects of smoking start to show. The regular cigarette cough, the discolored teeth, the stank that never goes away, the breathing difficulties become more evident, the skin destruction and color, etc. all contribute to people starting to think about quitting, rather than encouraging others to start smoking.

  2. Living on this planet with our dillusinal history causes mental illness. The armies of the world had cigarettes in all soldiers kits. How effn smart we are now.

  3. Charles G. Shaver | December 2, 2023 at 9:20 am | Reply

    I’ve been writing for years about correlation’s between very, very mild food (minimally) allergy reactions (e.g., Dr. Arthur F. Coca, by 1935), the 1980 US FDA approval of the expanded use of cultured “free” (unlike natural “protein-bound” can cross the blood brain barrier) monosodium glutamate (MSG, minimally), related inflammation in general and mind altering brain damage in particular (e.g., AD, dementia, depression, mass shootings and suicides, minimally). Despite my being an adult lifetime non-smoker raised in a smoking household, exposed to second hand smoke on the job and in social places until those were banned and testing allergic to tobacco in late 1981, I’ve almost never experienced the kind of mood swings and short term memory problems I get from very, very mild allergies to proteinaceous foods aggravated with FDA approved food poisoning, primarily added MSG. Wake-up mainstream medicine.

  4. For me personally this is the opposite story. Can we please just leave the smokers in peace and focus on the real causes of mental illness, one of which are articles such as these!

Leave a comment

Email address is optional. If provided, your email will not be published or shared.