Second hand smoke exposure is associated with psychological distress and risk of future psychiatric illness, according to new UCL research that suggests the harmful affects of passive smoking go beyond physical health.
The new research, published today in the Archives of General Psychiatry, examined the associations between mental health and second hand smoke (SHS) exposure - known as passive smoking - by measuring the circulating biochemical marker cotinine, which is found in saliva and can be used to measure levels of exposure to tobacco smoke. The study found that SHS exposure is associated with psychological distress and risk of future psychiatric illness in healthy adults.
A representative sample of 5,560 non-smoking adults and 2,689 smokers without history of mental illness were drawn from the 1998 and 2003 Scottish Health Surveys. A score greater than 3 on the 12-item General Health Questionnaire was employed as an indicator of psychological distress. Incident psychiatric hospital admissions over 6 years follow up were also recorded.
Psychological distress was apparent in 14.5% of the sample. In an analysis of the data, after adjustments for a range of potential confounding factors such as social status, high SHS exposure among non-smokers (cotinine levels between 0.70 and 15 micrograms per litre) was associated with 50% higher odds of reporting psychological distress in comparison with participants with cotinine levels below the limit of detection. Active smokers were also more likely to report psychological distress. The risk of future psychiatric illness was also related to high SHS exposure and active smoking.
Lead author Dr Mark Hamer, UCL Epidemiology & Public Health, said: "SHS exposure at home is growing in relative importance as restrictions on smoking in workplaces and public places spread. A growing body of literature has demonstrated the harmful physical effects of second hand smoke exposure, but there has been limited research about the affects on mental health.
"Animal data have suggested that tobacco may induce a negative mood, and some human studies have also identified a potential association between smoking and depression. Our data is therefore consistent with other emerging evidence to suggest a causal role of nicotine exposure in mental health. Importantly, this study advances previous research because we obtained an accurate assessment of SHS exposure using a valid biochemical indicator.
"Mental ill health accounts for almost 20% of the burden of disease in the European Region and can affect one in four people at some time in their life. Our findings emphasise the importance of reducing SHS exposure at a population level, not only for the benefit of our physical health but for our mental health as well."
'Objectively assessed second hand smoke exposure and mental health in adults: cross-sectional and prospective evidence from the Scottish Health Survey', will be published in the Archives of General Psychiatry 7th June 2010.