June 16, 2010 — Exposure to secondhand smoke (SHS) can lead to psychological distress and an increased risk for future psychiatric hospitalization in healthy, nonsmoking adults, according to a new longitudinal study drawn from the Scottish Health Surveys.
These findings "emphasize the importance of reducing SHS exposure at a population level not only for physical health but for mental health," write lead author Mark Hamer, PhD, associate professor of social epidemiology in the Department of Epidemiology and Public Health at University College London, England, and colleagues.
"People [in our study] with the highest SHS exposure reported being exposed in their home," Dr. Hamer told Medscape Psychiatry. "Therefore, the highest risks are likely to be in people living with a smoker."
He noted that previous studies in this area have used self-report measures, which can often be unreliable. "Our study employed objective measures using salivary cotinine. Also, [whereas] previous studies have been cross-sectional, we demonstrate some longitudinal associations, which strengthen our findings."
The study was published online June 7 in the Archives of General Psychiatry.
60% of Nonsmokers Exposed to SHS
It is estimated that 60% of American nonsmokers have biological evidence of exposure to SHS, according to the study authors. "In addition, SHS exposure at home is growing in relative importance as restrictions on smoking in workplaces and public places spread."
Although past studies have shown that SHS can cause a number of physical health effects, its association with mental health has not been known, said Dr. Hamer. "It is reasonable to think that [SHS] exposure might have effects on mental health because previous research suggests that active smokers have higher rates of depression and poorer mental health."
For this study, the investigators evaluated data on 5560 nonsmoking adults (mean age, 49.8 years; 45% men) and 2595 smokers (mean age, 44.8 years; 50.2% men) with no history of mental illness from the 1998 and 2003 Scottish Health Surveys. Nonsmokers included both never-smokers and ex-smokers.
Exposure to SHS among nonsmokers was assessed using a salivary cotinine sample; cotinine is a circulating biochemical marker of nicotine exposure. Low SHS exposure was defined as cotinine levels below the detectable limit (≤0.05 μg/L), low to moderate exposure was defined as levels between 0.06 and 0.30 μg/L, moderate exposure was defined as levels between 0.31 and 0.70 μg/L, and high exposure was defined as levels between 0.71 and 14.99 μg/L. Current smokers were defined by either self-report or cotinine levels of 15.00 μg/L or higher.
In addition, the participants filled out the 12-item General Health Questionnaires, which indicated psychological distress for scores greater than 3. A patient-based database of hospital admissions during 6 years of follow-up was prospectively linked to the surveys and was also evaluated.
High Distress, Hospitalization Risk
Results showed that "psychological distress was apparent in 14.5% of the entire sample," report the study authors.
After adjusting for covariates, the cross-sectional data found that nonsmokers had a higher risk for psychological distress after high SHS exposure (odds radio, 1.49; 95% confidence interval [CI], 1.13 - 1.97) than did those with low SHS exposure.
During the follow-up evaluation, the investigators also found a total of 41 new hospital admissions for depression, substance abuse, schizophrenia, nonspecific delirium, or other psychiatric conditions.
Prospective analyses showed that both high SHS exposure (adjusted hazard ratio [HR], 2.84; 95% CI, 1.07 - 7.59) and active smoking (adjusted HR, 3.74; 95% CI, 1.55 - 8.98) increased the risk for future psychiatric hospitalization.
"Our data are consistent with other emerging evidence to suggest a causal role of nicotine exposure in mental health," write the study authors. However, "further studies will be required to investigate the possible pathways through which SHS exposure influences mental health."
Dr. Hamer reported that his team of researchers now plans to look at associations between SHS and other health outcomes.
Study Raises Awareness
"This is an important study and one that really raises our awareness of the need to think more broadly when we're looking at health consequences, that we should equally be paying attention to mental health potential consequences," Douglas Ziedonis, MD, MPH, professor and chair of the Department of Psychiatry at the University of Massachusetts Medical School and UMass Memorial Healthcare System in Worcester, told Medscape Psychiatry.
"It was amazing for me to think that we haven't really done this type of a straightforward study looking at [SHS] in a prospective way and linking it with mental health symptoms," said Dr. Ziedonis, who was not involved with this trial.
He noted a recent study that showed a link between tobacco addiction and depression. "If that can happen with a smoker, it is definitely something that should be looked at in [SHS]."
Dr. Ziedonis also voiced some concerns with the items measured and reported on. "Psychiatric hospitalization by itself is not a great marker because there are so many factors that go into why people get hospitalized. However, it is something to at least queue up some level of severity. Hopefully, future studies will have more detail and a much broader range of psychiatric problems that might occur."
Overall, he said, the study has important implications for clinicians. "This might heighten our awareness to think about asking our patients, who we are treating for depression or anxiety, whether they smoke themselves and how that might play a role. And now, something we probably never thought about asking would be whether they're living with a smoker and then having conversations about whether they can reduce the amounts of [SHS] for the reason that it might be potentially worsening their mental health."
The study and/or authors were supported in part by the British Heart Foundation, the National Institute for Health, and a Wellcome Trust Career Development Fellowship. The Scottish Health Survey was supported by the Scottish Executive. The study authors and Dr. Ziedonis have disclosed no relevant financial relationships.
Arch Gen Psychiatry. Published online June 7, 2010.
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Cite this: Secondhand Smoke Linked to Psychiatric Illness, Hospitalization - Medscape - Jun 16, 2010.