Background Healthy ageing represents a major societal challenge for both the UK and China, with both countries facing a marked growth in ageing populations, but less clear is the role of modifiable risk factors such as lifestyle behaviours that could have cultural and regional influences. We aimed to investigate the impact of smoking on the age-related cognitive decline over 8 years follow-up period in a cross-country comparison of England and China.
Methods The data employed were from the English Longitudinal Study of Ageing (ELSA) (n=6,768) spanning over 8 years from wave 5 (20010/11) to wave 9 (2018/19), and the Chinese Health and Retirement Longitudinal Study (CHARLS) (n= 10,253) waves 1 (2011) to 4 (2018). We assessed the change in memory using immediate and delayed 10-word recall tests (max score 20) over 4 waves at every two-year follow-up within each of the two cohorts. Smoking was measured at baseline with a self-completion questionnaire. The covariates considered were age, sex, marital status, education, wealth, urbanicity, hypertension, heart problems, diabetes, depressive symptoms, and alcohol consumption. The association between smoking and cognitive decline was examined independently within each study by employing a coordinated analysis using linear mixed models and a similar set of covariates within each analytical sample.
Results In England, the baseline memory was (beta (β) =8.52, standard errors (SE)=0.20), p≤0.001, while the rate of memory change was estimated with a linear slope of β =-0.13, SE=0.03, p≤0.001 per year. In China, the baseline memory was β =7.01, SE=0.23, p≤0.001 and the linear slope of memory change over time was β =-0.39, SE=0.05, p≤0.001 per year.
We found a steeper memory decline for English participants who were smokers with β =-0.04, SE=0.02), p=0.044 yearly change in memory scores compared to non-smokers independent of all covariates. A slower decline in memory was also observed for Chinese smokers β =-0.4, SE=0.2, p=0.018 independent of all covariates. No associations were found between baseline smoking and baseline memory performance (intercept) within each study.
Conclusion The overall results imply a clear and consistent detrimental effect of smoking on the rate of memory decline over almost a decade in both England and China. Public health strategies for preventing cognitive decline should target smoking cessation and support individuals in adopting healthier lifestyles worldwide.
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