Smoking increases risk of mental health illnesses

A new University of Bristol study has found that tobacco smoking may increase someone’s risk of developing depression and schizophrenia.

Many studies have found that smoking is much more common amongst people with mental illness – especially depression and schizophrenia. But they have found it difficult to disentangle whether this is a cause-and-effect relationship, and if so in which direction. For example, does mental illness increase the likelihood of smoking, or is smoking itself a risk factor for mental illness?

The University of Bristol researchers looked at data from 462,690 individuals of European ancestry, comprising eight per cent current smokers and 22 per cent former smokers, and applied an analytic approach called Mendelian randomisation, which uses genetic variants associated with an exposure to support stronger conclusions about cause-and-effect relationships.

They found evidence that tobacco smoking increased risk of depression and schizophrenia, but also that depression and schizophrenia increase the likelihood of smoking, although the evidence was weaker in this direction.

The government's mental health task force made the recommendation in their 2016 review that psychiatric hospitals should be smoke free by 2018. The report authors argue that this new evidence adds further weight to support the implementation of smoke-free policies.

Robyn Wootton, senior research associate in the School of Psychological Science and the study's lead author, said: "Individuals with mental illness are often overlooked in our efforts to reduce smoking prevalence, leading to health inequalities. Our work shows that we should be making every effort to prevent smoking initiation and encourage smoking cessation because of the consequences to mental health as well as physical health."