Post-diagnosis smoking habit change and incident dementia in cancer survivors

Many individuals change their smoking habits after cancer diagnosis. We aimed to evaluate the association of post-diagnosis smoking habit change with incident dementia in cancer survivors.

We identified 558,127 individuals who were diagnosed with cancer at age ≥ 20 and survived for ≥ 3 years. Participants were classified into four groups: (1) sustained non-smokers, (2) initiators/relapsers, (3) quitters, and (4) continuing smokers. Dementia risk in each group was assessed using a cause-specific Cox model.

After cancer diagnosis, 2.3% of pre-diagnosis non-smokers initiated/relapsed into smoking, while 51.7% of pre-diagnosis smokers quit smoking. Compared to sustained non-smokers, multivariable-adjusted risk of dementia was 29% higher among initiators/relapsers, 11% higher among quitters, and 31% higher among continuing smokers. Compared to continuing smokers, the risk was 15% lower among quitters.

In cancer survivors, smoking initiation/relapse was associated with increased risk of dementia, whereas smoking cessation was associated with decreased risk of dementia.

Approximately half of pre-diagnosis smokers quit smoking after a cancer diagnosis. Smoking cessation was associated with a 15% reduced risk of dementia. More than 2% of pre-diagnosis non-smokers initiated or relapsed into smoking after a cancer diagnosis. Smoking initiation/relapse was associated with a 29% elevated risk of dementia.