研究者檢視了出生於1977年中期1,265位(635名男性以及630名女性)的資料，這些對象來自「Christchurch Health and Development Study」研究。
在該世代18、21和25歲時，使用組合型國際診斷性會談(Composite International Diagnostic Interview)詢問他們在過去12個月間是否有任何憂鬱症狀，以及使用精神疾病診斷與統計手冊第四版(Diagnostic and Statistical Manual of Mental Disorders, 4th Edition)、症狀準則，探討他們在過去一個月時的抽菸習慣。
研究者接著使用固定效應回歸模式校正研究第一階段時的干擾因素，使用結構式方程式模式方法(methods of structural equation modeling)校正第二階段，用來探討因果關係。
June 9, 2010 — Individuals who smoke cigarettes may increase their risk of developing depression, according to results from a large longitudinal study from New Zealand researchers.
The study also found that those who were dependent on nicotine were more than twice as likely to have depressive symptoms as those who were not dependent.
Lead researcher David M. Fergusson, PhD, professor and director of the Christchurch Health and Development Study at the University of Otago, Dunedin, New Zealand, said in a statement that the reason for the relationship between smoking and depression is unclear.
"However, it's possible that nicotine causes changes to neurotransmitter activity in the brain, leading to an increased risk of depression," said Dr. Fergusson.
"The main message of the paper is that in addition to the harm that smoking does to physical health, nicotine dependence may also increase risks of mental health problems," he told Medscape Psychiatry. "The message for clinicians, clearly, is to encourage smoking cessation amongst patients subject to recurrent depressive episodes."
The study was published June 1 in the British Journal of Psychiatry.
Pathways Unclear
Although there have been a number of recent studies that focused on the association between substance use and mental disorders, past research "has not elucidated the pathways by which smoking is associated with depression," write the study authors.
"Does [this association] reflect common factors [from] both smoking and depression? Or does depression increase rates of smoking? Or does smoking lead to depression? The aim of this study was to cast further light on an issue that had been debated for some years," said Dr. Fergusson.
The investigators examined data on 1265 people (635 men, 630 women), born in mid-1977, from the Christchurch Health and Development Study. The cohort participants were asked at the ages of 18, 21, and 25 years whether they had any symptoms of depression during the last 12 months, using the Composite International Diagnostic Interview, and about their smoking habits during the past month, using Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, symptom criteria.
The researchers then used fixed-effects regression modeling to adjust for confounding during the first stage of the study and methods of structural equation modeling for the second stage, which explored the direction of causality.
Significant Association
At the end of the study, the investigators found that "at each age, increasing levels of nicotine-dependence symptoms were significantly associated with increasing rates of depressive symptoms (P < 0.0001)."
In addition, "those reporting at least 5 symptoms of nicotine dependence had rates of depressive symptoms that were 2.13 times (95% confidence interval, 1.98-2.31) those of individuals who reported no symptoms of nicotine dependence."
After adjusting for confounding factors, significant associations were still found between nicotine dependence and symptoms of depression (P < .05).
The researchers also found that although the "nicotine-dependence symptoms were significantly related to depressive symptoms, depressive symptoms were not significantly related to nicotine-dependence symptoms (P = 0.21)."
This means that smoking increased the risk of developing depressive symptoms, not that smoking was increased as a result of the participants being depressed, explain the study authors.
They caution, however, that their study does not prove that smoking causes depression and that it "should be viewed as suggestive rather than definitive."
Dr. Fergusson reported that the next step "is clearly further brain research examining the possible pathways that may link nicotine dependence and mood states."
"It will also be of interest to conduct randomized trials of smoking cessation in depressed patients to determine the extent to which [it] may reduce risks of further depressive episodes," he added.
This study was supported by grants from the Health Research Council of New Zealand, the National Child Health Research Foundation, the Canterbury Medical Research Foundation, and the New Zealand Lottery Grants Board. Dr. Fergusson has disclosed no relevant financial relationships.
