Smoking has long been suspected to contribute to cognitive decline, but uncertainty has persisted regarding its relationship with specific dementia subtypes and whether quitting smoking alters long-term risk. To explore these issues, the researchers conducted a longitudinal closed cohort study using data from the Trøndelag Health Study (HUNT), one of the largest health surveys in Norway. The analysis focused on smoking as an independent risk factor for all-cause dementia, as well as vascular and Alzheimer’s dementia.
The study included 8,532 participants with a mean baseline age of 56.3 years. Smoking status was self-reported during the HUNT2 survey conducted between 1995 and 1997, and cognitive status was assessed approximately two decades later during the HUNT4 70+ examination between 2017 and 2019. Participants were followed for an average of 21.8 years. Smoking exposure was further quantified using pack-years, defined as smoking 20 cigarettes per day for one year.
The following were the key findings:
- At baseline, 21% of participants were current smokers, 34.4% were former smokers, and 44.8% had never smoked.
- During follow-up, 1,305 participants, accounting for about 15% of the cohort, were diagnosed with dementia.
- After adjustment for covariates, current smoking was associated with a 31% higher risk of all-cause dementia compared with never smoking.
- The association was stronger among participants younger than 85 years at follow-up.
- Among those younger than 85 years, current smoking was linked to a 54% higher risk of dementia in women and a 36% higher risk in men.
- No significant association between smoking and dementia risk was observed in participants aged 85 years or older.
- Current smoking was strongly associated with an increased risk of vascular dementia, with more than a twofold higher risk overall.
- The highest vascular dementia risk was seen in participants younger than 85 years, particularly men.
- Smoking was not significantly associated with the risk of Alzheimer’s dementia.
- Former smoking was not linked to all-cause dementia, though former male smokers younger than 85 years had an increased risk of vascular dementia.
- Cumulative smoking exposure, measured as pack-years, was not significantly associated with dementia risk.
The authors highlighted the public health implications of these findings, noting that smoking appears to be a modifiable risk factor for dementia, particularly vascular dementia. They emphasized that the results support early preventive strategies and targeted public health efforts to reduce smoking-related cognitive decline. Importantly, the lack of a strong association among former smokers adds to growing evidence that smoking cessation may help lower long-term dementia risk.
Reference:
Myrstad, C., Larssen, M., Engdahl, B. et al. Smoking is associated with increased risk for dementia: the HUNT study, Norway. BMC Public Health (2025). https://doi.org/10.1186/s12889-025-25813-3
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