Background: Both cigarette smoking and diabetes mellitus are well-established risk factors for development of dementia. However, the interaction between smoking and diabetes is yet unknown.
Objective: In this study, we clarify association between smoking, diabetes, and dementia risk in older adults.
Methods: Participants in this study included community residents aged 65 years and older who had participated in a health checkup in 2006, followed for 10 years (n = 9,403) and had long-term care insurance information data. Furthermore, the risk estimates of smoking status and diabetes diagnosis on dementia adjusted for the competing risk of death prior to dementia were analyzed.
Results: During follow-up, 2,647 participants developed dementia. The smoking status-diabetes interaction on development of dementia was statistically significant (p≤0.001). Among those patients exposed to both factors, 17% of risk of development of dementia was attributable to the interaction of these factors. Current smokers with diabetes had significantly greater risks of development of dementia than never smokers without diabetes (reference): multivariable-adjusted risk of dementia in current smokers without diabetes (subdistribution hazard ratio [sHR], 1.25; 95% confidence interval [CI], 1.05-1.48); never smokers with diabetes (1.31, 1.16-1.47); and current smokers with diabetes (1.86, 1.39-2.48). However, no such association was noted for former smokers with and without diabetes.
Conclusions: Current smoking, but not former smoking, was associated with increased risk of development of dementia in older adults with and without diabetes. Moreover, the synergistic effect of current smoking and diabetes on dementia was noted.
Keywords: Cigarette smoking; dementia; diabetes mellitus; insurance; long-term care.