Smoking and obesity have been newly linked to depression among women.
A research team led by Suh Byung-seong of Sungkyunkwan University's Gangbuk Samsung Hospital analyzed history of smoking, drinking, obesity, hypertension, metabolic syndrome, diabetes, depression, anxiety and sleeping disorders of 65,309 office workers between 20 and 39 who were checked at one university hospital in Seoul in 2011.
They found that among women, smoking and obesity are highly correlated with the risk of depression, whereas the other factors are not. No such correlation was found for men.
Using the Center for Epidemiologic Studies Depression Scale (CES-D) questionnaire, the researchers grouped the subjects into normal, risk, and high-risk groups.
The percentage of women who smoked and were in the high-risk group was 1.89 times higher than among non-smokers. That of women who were obese and in the high risk group was 1.48 times higher than that of women of normal weight.
Suh said, "Smoking increases nicotine in the body and temporarily increases the levels of dopamine and serotonin," which are hormones linked to happiness.
"However, repeated smoking decreases these hormones and can increase the risk of depression. Similar physiological evidence is being discovered elsewhere, and many academics now argue that smoking is an antecedent factor of depression," he added.
Obesity disrupts the balance of neurotransmitters, and this may trigger depression.
Since the prevalence of depression among men is only one-fourth that of women, no correlation between depression and smoking or obesity was found.