Led by researchers
from the University of Bristol’s Tobacco and Alcohol Research Group (TARG), the
study was supported by Bristol’s MRC Integrative Epidemiology Unit (IEU) and
the NIHR Bristol Biomedical Research Centre (BRC). The study authors used UK Biobank
data from 462,690 individuals of European ancestry, which comprised of 8%
current smokers and 22% former smokers.
The
research team applied the Mendelian randomisation, an analytic approach which
uses genetic variants associated with an exposure, such as exposure to
cigarette smoke, in order to derive conclusions about
cause-and-effect relationships. The analysis indicated that tobacco smoking
increased the risk for depression and schizophrenia, and also that vice versa,
depression and schizophrenia increase the likelihood of smoking.
“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.”-Dr.
Robyn Wootton, Senior Research Associate, School of Experimental Psychology
“There was strong
evidence to suggest smoking is a risk factor for
both schizophrenia (odds ratio (OR) 2.27, 95% confidence interval (CI)
1.67–3.08, p<0.001) and depression (OR 1.99, 95% CI 1.71–2.32, p<0.001).
Results were consistent across both lifetime smoking and smoking initiation. We
found some evidence that genetic liability to depression increases smoking (β =
0.091, 95% CI 0.027–0.155, p = 0.005) but evidence was mixed for schizophrenia
(β = 0.022, 95% CI 0.005–0.038, p = 0.009) with very weak evidence for an
effect on smoking initiation,” read the study Abstract.
Smoking linked to
bipolar disorder
Earlier
this year, the same research team published a study in the British Journal,
indicating that tobacco smoking increases the risk for bipolar disorder. In
line with these findings, in 2016, the UK government’s mental health task force
had recommended that psychiatric hospitals should be smoke free by 2018.
“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,” said Dr. Robyn Wootton, Senior Research Associate in
the School of Experimental Psychology and the study’s lead author.
Senior
study author and Professor of Biological Psychology in Bristol’s School of
Psychological Science, Marcus Munafò, added: “The increasing availability of
genetic data in large studies, together with the identification of genetic
variants associated with a range of behaviours and health outcomes, is
transforming our ability to use techniques such as Mendelian randomisation to
understand causal pathways. What this shows is that genetic studies can tell us
as much about environmental influences—in this case the effects of smoking on mental
health—as about underlying biology.”