Longitudinal changes in smoking habits over 20 years and late-life depressive symptoms: The Singapore Chinese Health...

Its uncertain how rapidly the detrimental effects of smoking on depression decline after cessation. Hence, we investigated the association between changes in smoking habits and late-life depressive symptoms.

We used data from 5247 men in the Singapore Chinese Health Study. Smoking was assessed at baseline (mean age of 52.5 years; 1993-98), follow-up 1 (mean age of 58.7 years; 1999-2004), follow-up 2 (mean age of 65.5 years; 2006-10) and follow-up 3 interviews (mean age of 72.8 years; 2014-16). Participants were categorized according to smoking status at baseline and subsequent follow-ups. Late-life depressive symptoms were measured using the 15-item Geriatric Depression Scale at follow-up 3. Logistic regression models were used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) of depressive symptoms.

Compared to never-smokers, while the multivariable-adjusted OR (95% CI) for depression was 2.19 (1.78-2.70) in persistent smokers, this risk was reduced progressively with increasing duration of cessation. Specifically, the OR (95% CI) was 1.39 (1.03-1.88) in those quitting for <10 years and substantially reduced to 1.11 (0.86-1.44) in those quitting for ≥30 years. Expectantly, earlier age at cessation was associated with a greater reduction in the likelihood; the OR (95% CI) was 1.39 (1.08-1.79) in those quitting 60 years and older, whereas it was 1.06 (0.79-1.43) in those quitting before 40 years old compared to never-smokers.

The deleterious effects of smoking on late-life depression were substantially reduced only after sustained quitting for ≥30 years or quitting before 40 years old.