By Bruce Bower, Science News
Where there’s secondhand cigarette smoke, there’s emotional fire. As exposure to cigarette fumes increases among nonsmokers, so does their risk of developing serious psychological distress and of being hospitalized for mental ailments, a new study finds.
Cigarette smokers have been shown to have more psychological problems than nonsmokers do, and new evidence suggests that nonsmokers who inhale high levels of secondhand smoke may experience nearly as much psychological distress as smokers, say epidemiologist Mark Hamer of University College London and his colleagues. Overall, these findings support the view, largely based on animal studies, that nicotine administered in large enough doses can induce sadness and other negative moods, the researchers propose in the August Archives of General Psychiatry.
“Our data are preliminary, but there is a strong possibility that the observed association reflects a causal link,” Hamer says.
Previous research suggests that nicotine alters mood by disrupting immune responses, stress-hormone regulation and the transmission of dopamine, a chemical messenger in the brain. But little is known about nicotine’s possible relationship to specific psychiatric disorders.
The link between nicotine exposure and mood held up after statistically accounting for participants’ social status, alcohol use, physical activity level, body mass index, chronic physical illness, level of psychological distress upon entering the study and previous hospitalizations for mental illness.
A related study, published in the January Psychosomatic Medicine, found an increased risk for depression symptoms among nonsmokers exposed to modest or greater levels of secondhand smoke. A team led by epidemiologist David J. Lee of the University of Miami Miller School of Medicine examined data from a 2005–2006 survey of nearly 3,000 U.S. adults.
Given widespread exposure to secondhand cigarette smoke, further research on its relation to mental health is warranted, Hamer asserts. A 2006 federal report estimated that 60 percent of nonsmokers in the United States display biological signs of having ingested at least low levels of nicotine via cigarette smoke.
Despite Hamer’s new evidence, scientists cannot rule out that people who experience especially stressful home and work lives are also most likely to encounter secondhand smoke and to develop serious psychological problems, Lee remarks. One promising research direction would be to examine whether policies that ban smoking in public or on the job lead to reductions in depression, anxiety and psychiatric hospitalizations, he says.
Hamer’s team studied 5,560 nonsmokers and 2,595 smokers, with average ages in the mid- to late 40s. Participants came from a nationally representative sample in Scotland that was surveyed in 1998 and 2003 about a variety of health issues. Volunteers completed a 12-item questionnaire that measured psychological distress by inquiring about sleep problems, general levels of happiness and symptoms of depression and anxiety in the previous month.
Saliva levels of cotinine, a breakdown product of nicotine, allowed the researchers to identify nonsmokers who had experienced low, moderate or high exposure to secondhand smoke. Cotinine levels also served to confirm self-reported cigarette use.
In 1998, psychological distress affected 9 percent of nonsmokers with low secondhand smoke exposure, 11 percent of nonsmokers with moderate secondhand smoke intake and 14 percent of those who frequently breathed secondhand smoke. Psychological distress occurred in 20 percent of smokers.
Over an average follow-up period of nearly six years, 41 study participants were admitted to psychiatric hospitals, mostly for depression and substance abuse. Psychiatric cases clustered among current smokers and participants with high secondhand smoke exposure.
Prior research has found that psychotic disorders occur at elevated rates among marijuana users. It’s not clear whether marijuana smoking contributed to elevated cotinine levels and at least some mental ailments that were seen among cigarette abstainers in the new study, Hamer notes. Self-reports of marijuana use were not collected in the Scottish investigation.