Smoking tobacco may increase the risk of depression and schizophrenia, according to a new study.
Researchers at the University of Bristol evaluated that people with depression and schizophrenia are also more likely to start smoking.
The study, published in the journal of psychological medicine, analysed genetic data from 462,690 people from European ancestry to evaluate the cause-and-effect relationships with smoking tobacco.
Researchers used the Mendelian randomisation technique, which identified genetic variations associated with exposure, such as smoking, and examine whether the relationship is causal.
Results show high lifetime smokers were almost 2.5 times as likely to develop schizophrenia (from an odds ratio of 2.27) and almost twice as likely to develop depression (from an odds ratio of 1.99).
The study also reveals evidence supporting why smoking rates are so high amongst people with schizophrenia and depression.
The report said: ‘We found evidence to suggest that genetic liability for schizophrenia and depression increases lifetime smoking. This supports previous observational evidence and might explain why smoking rates remain so high amongst individuals with schizophrenia and depression compared with the general population.’
It follows a similar study published earlier this year by the same researchers, showing tobacco smoking increases the risk of bipolar disorder.
The study concluded: ‘These findings suggest that the association between smoking, schizophrenia and depression is due, at least in part, to a causal effect of smoking, providing further evidence for the detrimental consequences of smoking on mental health.’
Dr Robyn Wootton, senior research associate in the School of Psychological Science and 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.’
Recent official data from NHS Digital showed the number of young people taking up smoking is at its lowest ever rate, although the use of e-cigarettes has risen.