Best to quit early to mitigate the effect of smoking on late-life depression

Persistent smoking raises the likelihood of experiencing late-life depressive symptoms in Asians, and this likelihood decreases only after 30 years of sustained cessation, according to local research.

Analysis of data from a cohort of men in the Singapore Chinese Health Study showed that compared with never smokers, chronic smokers had greater odds of having depressive symptoms after a median follow-up of 19.7 years. [J Affect Disord 2026;doi:10.1016/j.jad.2026.121177]

The highest odds were observed for those who started smoking as a teenager (<15 years: odds ratio [OR], 2.57, 95 percent confidence interval [CI], 1.77–3.74; 15–19 years: OR, 2.05, 95 percent CI, 1.53–2.73; p<0.001 for trend), those who smoked heavily (≥33 cigarettes per day: OR, 2.25, 95 percent CI, 1.39–3.65; p<0.001 for trend), and those who had smoked for decades (≥60 years: OR, 2.53, 95 percent CI, 1.79–3.57; p<0.001 for trend).

More importantly, the probability of depression in later life remained significantly elevated among individuals who ceased smoking late or who smoked again after quitting. On the other hand, it was substantially reduced—with estimates approaching null and lacking statistical significance—among those who sustained smoking cessation in the long term, the investigators noted.

The corresponding ORs for depression in later life were 1.15 (95 percent CI, 0.94–1.41) among long-term quitters (average quitting duration of 31.3 years), 1.23 (95 percent CI, 0.87–1.74) among moderate-term quitters (average quitting duration of 18.6 years), 1.53 (95 percent CI, 1.10–2.12) among short-term quitters (average quitting duration of 11.1 years), 1.42 (95 percent CI, 1.01–2.01) among recent quitters (average quitting duration of 4.1 years), 1.73 (95 percent CI, 1.19–2.51) among quitters who relapsed, and 2.18 (95 percent CI, 1.77–2.69) among persistent smokers vs never smokers.

The mean age at quitting was 50.3 years for persistent quitters, and only those who quit at age <40 years had a reduced likelihood of depressive symptoms compared with never-smokers (OR, 1.06, 95 percent CI, 0.79–1.43).

“Our research extends prior findings by tracking participants every 5–7 years over a 20-year period, with detailed information on the timing and age of cessation. This approach allowed us to uniquely delineate various durations of cessation and revealed that the risk of late-life depression could be mitigated only among individuals who quit early in life and maintained long-term cessation,” the investigators pointed out.

The link between smoking and increased vulnerability to depression has been explored extensively, and studies showing that structural and functional brain impairments in smokers could take decades to recover or may remain partially irreversible due to age-related declines in regenerative capacity and neuronal repair processes explain the biological plausibility of our findings, they said. [Biol Psychiatry Glob Open Sci 2024;4:74-82; Mol Psychiatry 2015;20:778-785]

Coordinated efforts among governments, public health officials, and other stakeholders are needed to control the smoking epidemic and prevent age-related depression at the population level, according to the investigators. These should include personalized cessation interventions that promote lifelong abstinence from smoking.

The study included 5,247 men who participated in the Singapore Chinese Health Study, of which 21.1 percent had depressive symptoms in late life. Smoking was assessed at baseline (mean age 52.5 years), follow-up 1 (mean age 58.7 years), follow-up 2 (mean age 65.5 years), and follow-up 3 (mean age 72.8 years). Late-life depressive symptoms were evaluated using the 15-item Geriatric Depression Scale at follow-up 3.