A new study published today [Wednesday 6 November] in Psychological Medicine and led by University of Bristol researchers has found that tobacco smoking may increase your risk of developing depression and schizophrenia.
It is well-known that smoking is much more common amongst people with mental illness – especially depression and schizophrenia. However, most studies that have looked at this association have not been able to disentangle whether this is a cause-and-effect relationship, and if so in which direction. Does mental illness increase the likelihood of smoking, or is smoking itself a risk factor for mental illness?
Researchers from the University's Tobacco and Alcohol Research Group (TARG) with support from Bristol's MRC Integrative Epidemiology Unit (IEU) and the NIHR Bristol Biomedical Research Centre (BRC), used UK Biobank data from 462,690 individuals of European ancestry, comprising eight per cent current smokers and 22 per cent former smokers.
The team applied an analytic approach called Mendelian randomisation, which uses genetic variants associated with an exposure (e.g. smoking) 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 for schizophrenia).
The study adds to a growing body of work suggesting that smoking can have adverse effects on mental health. The same group published a similar study in British Journal of Psychiatry earlier this year in collaboration with the University of Amsterdam, showing evidence that tobacco smoking increases the risk of bipolar disorder.
The UK government's mental health task force made the recommendation in their 2016 review that psychiatric hospitals should be smoke free by 2018. This new evidence adds further weight to support the implementation of smoke-free policies. Not only is there evidence that smoking can be detrimental for mental health, but much of the excess mortality associated with mental illness is due to smoking.
Dr 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."
Marcus Munafò, Professor of Biological Psychology in Bristol's School of Psychological Science and senior author on the study, 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."
Paper
'Evidence for causal effects of lifetime smoking on risk for depression and schizophrenia: A Mendelian randomisation study' by Robyn Wotton, Marcus Munafò et al in Psychological Medicine [open access]
Further information
About the Tobacco and Alcohol Research Group (TARG)
TARG conduct research into the psychological and biological factors underlying health behaviours. We are part of the MRC Integrative Epidemiology Unit (MRC IEU) at the University of Bristol.
About UK Biobank
UK Biobank is a major national and international health resource, and a registered charity in its own right with the aim of improving the prevention, diagnosis and treatment of a wide range of serious and life-threatening illnesses – including cancer, heart diseases, stroke, diabetes, arthritis, osteoporosis, eye disorders, depression and forms of dementia. UK Biobank recruited 500,000 people aged between 40-69 years in 2006-2010 from across the country to take part in this project. They have undergone measures, provided blood, urine and saliva samples for future analysis, detailed information about themselves and agreed to have their health followed. Over many years this will build into a powerful resource to help scientists discover why some people develop particular diseases and others do not.
About the National Institute for Health Research (NIHR)
The National Institute for Health Research (NIHR) is the nation's largest funder of health and care research. The NIHR:
- Funds, supports and delivers high quality research that benefits the NHS, public health and social care
- Engages and involves patients, carers and the public in order to improve the reach, quality and impact of research
- Attracts, trains and supports the best researchers to tackle the complex health and care challenges of the future
- Invests in world-class infrastructure and a skilled delivery workforce to translate discoveries into improved treatments and services
- Partners with other public funders, charities and industry to maximise the value of research to patients and the economy
The NIHR was established in 2006 to improve the health and wealth of the nation through research, and is funded by the Department of Health and Social Care. In addition to its national role, the NIHR supports applied health research for the direct and primary benefit of people in low- and middle-income countries, using UK aid from the UK government.
About NIHR Bristol BRC
The research centre, awarded to University Hospitals Bristol NHS Foundation Trust (UH Bristol) and the University of Bristol by the NIHR, conducts cutting-edge research to develop new, ground-breaking treatments, diagnostics, prevention and care for patients in a wide range of diseases.
Led by John Iredale (Bristol Pro Vice Chancellor for Health) and Jonathan Sterne, NIHR Bristol BRC has research themes on Cardiovascular Research (led by Gianni Angelini) Nutrition, Diet and Lifestyle (led by Andy Ness), Mental Health (led by David Gunnell), Perinatal and Reproductive Health (led by Debbie Lawlor) and Surgical Innovation (led by Jane Blazeby). The research themes are underpinned by cross-cutting themes in Translational Population Science (led by George Davey Smith) and Biostatistics, Evidence Synthesis and Informatics (led by Jonathan Sterne).
A strand of population health science runs through all themes of the BRC, with a focus on translating scientific discoveries that have arisen from population science into better care for NHS patients.
About the MRC Integrative Epidemiology Unit
The Medical Research Council Integrative Epidemiology Unit at the University of Bristol (IEU) is one of the MRC’s flagship University Units. The IEU brings together an innovative collection of research programmes and cross-cutting themes, underpinned by core research activities that will collectively fuel a step-change in causal analysis and their application. The aim of the MRC IEU is to apply the novel causal methods developed in the IEU to key research questions related to causes of bone, cardiometabolic, reproductive, mental and other aspects of ill-health; and to ensure that the results from these studies are appropriately translated into clinical/public health practice and industrial partnerships. A major focus of IEU activities is the integration of omic measures (genomic, epigenomic, transcriptomic and metabolomic) into epidemiological investigations.
