Smoking is associated with certain types of psychological disorders. Research has shown that the severity of depressive symptoms is directly related to the number of cigarettes smoked per day.

The relationship between smoking and depression has long been a topic of discussion in scientific circles. Scientists have established that there is an interdependence between these factors, as well as a dose-dependent effect. Additionally, experts note that smoking may be one of the factors contributing to the development of schizophrenia. Although the link between smoking and mental disorders has been confirmed, questions remain about the nature of this connection: is smoking a cause or a consequence of depression, how does the number of cigarettes affect the severity of symptoms, and to what extent can quitting smoking improve mental health?

A recent large-scale study published in BMC Public Health was conducted using data from NAKO, one of the largest population studies in Europe. The analysis included information on 173,000 participants aged 19 to 72. To assess depression, three methods were used: self-report of a doctor-diagnosed condition, a structured diagnostic interview to identify lifetime depressive episodes, and a questionnaire to measure current symptoms. Smoking was thoroughly characterized by status (current, former, never smoked), age of initiation, number of cigarettes per day, and time since quitting.

The results confirmed a general association between smoking and depression. Both current and former smokers had a significantly higher risk of both lifetime depression diagnosis and current depressive symptoms compared to those who had never smoked. The most pronounced indicators were observed among current smokers. Patterns were also identified that suggest a causal relationship: an increase in the number of cigarettes smoked per day was directly linked to more severe depressive symptoms.

Furthermore, an earlier age of smoking initiation was statistically associated with an earlier onset of depression. For the vast majority of participants (93.8%), smoking began before their first depressive episode, which may indicate a "vicious cycle" where smoking contributes to the development of depressive symptoms, which in turn encourage continued smoking.

Researchers also noted the positive effect of quitting smoking. The longer a person refrains from smoking, the longer the period of remission from depression and the less severe the existing symptoms.

Thus, the study showed that quitting smoking not only prevents the worsening of the problem but also contributes to the gradual improvement of mental health. The link between smoking and depression is not only proven but also has a cumulative effect.