文章轉錄自Science Daily（點此連結）；文章主要論述：「常暴露在二手菸的人或吸菸者」比「不常暴露在二手菸的人或不吸菸者」更容易因憂鬱、精神分裂、譫妄(delirium)與其他精神狀況而接受住院治療。或許，對於此研究結果，能以用環境或社經因素來解釋相關及可能的中間變項，譬如：由於處於高壓的工作環境，更易促使人吸菸並產生精神疾病；父親能肆無忌憚地在家中抽煙，這類家庭可能是比較高壓權威的管教與相處方式，所以使得暴露在二手菸的家人更易罹患精神疾病；但，這篇研究其實更想證明：暴露於尼古丁下與罹患精神疾病的因果關係，屬於物質對精神的直接影響。乍聽之下，覺得這因果的關係有點遙遠，怎麼可能抽煙的尼古丁和精神疾病竟然有直接關聯？但如果我們都能接受精油療法、香精療法的可能性，何以不相信這篇研究的結果呢？只是，中間作用的因果關係仍須釐清即是。

Secondhand Smoke Associated With Psychiatric Distress, Illness

ScienceDaily (June 8, 2010) — Exposure to secondhand smoke appears to be associated with psychological distress and the risk of future psychiatric hospitalization among healthy adults, according to a report posted online that will appear in the August print issue of Archives of General Psychiatry.

"A growing body of literature has demonstrated the harmful physical health effects of secondhand smoke exposure," the authors write as background information in the article. "Given the highly prevalent exposure to secondhand smoke -- in the United States, an estimated 60 percent of American non-smokers had biological evidence of exposure to secondhand smoke -- even a low level of risk may have a major public health impact."

Mark Hamer, Ph.D., of University College London, and colleagues studied 5,560 non-smoking adults (average age 49.8) and 2,595 smokers (average age 44.8) who did not have a history of mental illness and participated in the Scottish Health Survey in 1998 or 2003. Participants were assessed with a questionnaire about psychological distress, and admissions to psychiatric hospitals were tracked over six years of follow-up. Exposure to secondhand smoke among non-smokers was assessed using saliva levels of cotinine -- the main product formed when nicotine is broken down by the body -- "a reliable and valid circulating biochemical marker of nicotine exposure," the authors write.

A total of 14.5 percent of the participants reported psychological distress. Non-smokers with a high exposure to secondhand smoke (cotinine levels between 0.70 and 15 micrograms per liter) had higher odds of psychological distress when compared with those who had no detectable cotinine.

Over the six-year follow-up, 41 individuals were newly admitted to psychiatric hospitals. Smokers and non-smokers with high exposure to secondhand smoke were both more likely than non-smokers with low levels of secondhand smoke exposure to be hospitalized for depression, schizophrenia, delirium or other psychiatric conditions.

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. "Taken together, therefore, our data are consistent with other emerging evidence to suggest a causal role of nicotine exposure in mental health," the authors write.

"To our knowledge, this is the first study to demonstrate a prospective association between objectively assessed secondhand smoke exposure and mental health in a representative sample of a general population," they conclude.