Smoking could increase risk of depression and bipolar disorder

Researchers of this study utilized data from the UK Biobank, collected from over 330,000 participants. They calculated participants’ polygenic risk scores for traits including ever-smoking, smoking duration, and neuroticism (a tendency toward negative emotional states)

These scores helped measure someone’s genetic likelihood of developing certain smoking habits and mental illness.

Researchers found that participants were more likely to have started smoking before hospitalization for mental illness.

Their analysis further supported that the risk for hospitalization from mental illness was highest for current smokers and lowest for people who had never smoked.

The risk was moderately higher for people who had previously smoked than those who had never smoked.

The study authors summarize critical points of their findings thus:

“Genetic liability for smoking intensity has a crossover effect on hospitalization for major depression, bipolar disorder, and schizophrenia. Smoking behaviors have the same magnitude of effect on mental health hospitalization as genetic liability.”

So, if a person is genetically predisposed to smoking heavily, this same genetic factor could also increase their chances of being hospitalized due to severe mental health conditions.

In addition, the effects of smoking nicotine, regardless of a person’s genes, could raise their risk of hospitalization related to mental health issues just as much as their genetic risk does.

While the study cannot strictly prove that smoking causes mental illness, it does indicate a possible causal relationship.

It suggests the need for further research and addressing mental illness as an effect of smoking. More research is also needed about the underlying mechanisms involved if smoking really is a cause of mental illness.

Professor of biological psychology at the University of Bristol, United Kingdom, and MRC Investigator within the MRC Integrative Epidemiology Unit at the University of Bristol, Dr. Marcus Munafo, not involved in the study, commented on the findings for Medical News Today.

“Smokers typically believe that smoking reduces stress and anxiety. However, there is clear evidence that this is — in part at least — due to the relief of withdrawal after a period of not smoking, even as little as a few hours. This has contributed to the belief that smoking may help ameliorate symptoms of anxiety and depression, a narrative promoted by the tobacco industry,” he pointed out.

“Now, there is growing evidence that the clear association between smoking and mental health may — again, in part — be due to smoking being a causal risk factor for poor mental health. Although the evidence is not yet definitive, it is growing, and this study contributes to that evidence base,” said Dr. Munafo.

One chief limitation of the current study is the fact that the researchers specifically focused their analysis on participants of white British ancestry.

Furthermore, data from the UK Biobank also may not include an accurate number of individuals with even more severe mental illness. These factors make it difficult to generalize the results and indicate the need for more diverse research in the future.

Some data were also self-reported by the participants, so they may not be entirely accurate. Researchers also did not include certain risk factors in their models that may have contributed to mental disorders.

Then, the analysis did not address certain issues, such as how the course of a mental illness may change when a person starts to smoke, or adjust for socio-economic deprivation.

Researchers also note that they did not have a biological assay for smoking. They were also specifically looking at mental illness based on hospital stays and visits rather than mental illnesses treated in the outpatient setting.

They note that further research could include even younger participants, which could help to test and re-confirm the study’s findings.

Finally, genetics may also only play so much of a role in the risk of smoking and mental illness. Researchers note that one limitation of their research was that “[t]he heritability of pack-years, ever smoking, and neuroticism were low compared to twin studies.”

Overall, this study contributes to growing evidence that helping people quit smoking can offer many health benefits, including reducing their risk of severe mental illness.

Professor of behavioral medicine with the Nuffield Department of Primary Care Health Sciences at the University of Oxford in the U.K., Prof. Paul Aveyard, not involved in the study, noted the following to MNT:

“For a long time, professionals caring for people with mental illnesses have regarded smoking as a necessary coping mechanism. This attitude is changing because the evidence is increasing that smoking is a causal factor in mental illness and that stopping smoking may ameliorate it. Given the main cause of early onset non-communicable disease [is] preventable cardiovascular problems, supporting people to stop smoking should now be an imperative in services for people with mental illness.”

Quitting smoking can be a challenge, often requiring help from medical professionals and family and friends. Several resources are available, including support from counselors who can offer coaching and strategies to help with the challenges of quitting.

Doctors can also help by giving prescription medications that assist with some unpleasant side effects of quitting.

Friends and family can also create a supportive environment, such as by removing temptations for smoking and understanding common withdrawal symptoms. Using an individualized plan and support, a person who smokes can set themselves on a healthier path, physically and mentally.