Tobacco smoking and risk for dementia: evidence from the 10/66 population-based longitudinal study

Abstract

Objective: This study aimed to estimate the association between tobacco smoking and risk for dementia in seven low- and middle-income countries.

Methods: Secondary analysis of the 10/66 population-based cohort study was conducted with 11,143 dementia-free individuals aged 65 years and older who were followed-up for an average of 3.8 years totalling 42,715 person-years. Cox regression with competing-risk analyses was used, controlling for age, gender, number of assets, past hazardous drinking, exercise and self-report of heart disease. Exposure was measured in packyears and smoking status. The number of packyears was calculated by multiplying the average number of packs per day by years of consumption up to 50 years old and up to age at baseline.

Results: Meta-analysis of the results from each country yielded non-significant pooled relative risk ratios for all comparisons. There was no difference in risk for any dementia between ‘ever smokers’ compared to ‘never smokers’ (HR 0.96; 95% CI 0.82–1.13); ‘current smokers’ compared to ‘never smokers’ (HR 0.83; 95% CI 0.66–1.06); ‘former smokers’ compared to ‘never smokers’ (HR 1.06; 95% CI 0.88–1.27); ‘current smokers’ compared to ‘former smokers’ (HR 0.86; 95% CI 0.66–1.13). Results were similar for Alzheimer’s disease (AD) and Vascular Dementia (VaD) as outcomes. Lifetime tobacco consumption (packyears) was not associated with any dementia (HR 1.00; 95% CI 0.99–1.00), nor with AD or VaD.

Conclusion: Pooled results from all the countries showed no significant association between smoking and the onset of any dementia. Selective quitting in later-life might have biased the results towards no effect.

Keywords:

• Dementia
• smoking
• risk factors
• longitudinal studies
• prevention

Acknowledgment

We thank the 10/66 Dementia Research Group for providing us with the database used in this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This is a secondary analysis of data collected by the 10/66 Dementia Research Group (www.alz.co.uk/1066). The 10/66 DRG is led by Martin Prince from Institute of Psychiatry, Psychology and Neuroscience, King's College London. The other principal investigators, data custodians and responsible for research governance in each site are Juan Llibre Rodriguez (Cuba), Daisy Acosta (Dominican Republic), Mariella Guerra (Peru), Aquiles Salas (Venezuela), Ana Luisa Sosa (Mexico), KS Jacob (Vellore, India), Joseph D Williams (Chennai, India), Ivonne Jimenez (Puerto Rico) and Yueqin Huang (China). The 10/66 Dementia Research Group's research has been funded by the Wellcome Trust Health Consequences of Population Change Programme (GR066133 – Prevalence phase in Cuba and Brazil; GR080002- Incidence phase in Peru, Mexico, Argentina, Cuba, Dominican Republic, Venezuela and China), the World Health Organization (India, Dominican Republic and China), the US Alzheimerhx0027;s Association (IIRG – 04 – 1286 - Peru, Mexico and Argentina), the Puerto Rico State Legislature (Puerto Rico), and FONACIT/ CDCH/ UCV (Venezuela).