Associations among smoking, sleep quality, and decline in Mini-Mental State Examination scores based on health check-up data in Japan: a case-control study.

The number of individuals with age-related mild cognitive impairment and subsequent dementia has inevitably increased with the rise in population aging. It is important to maintain cognitive function or decelerate declines in cognitive function. However, the evidence on lifestyle-based factors associated with this decline is lacking. Here, we investigated modifiable lifestyle-based factors associated with chronological cognitive decline in cognitively healthy adults aged ≥60 years (Mini-Mental State Examination [MMSE] score ≥27). This case-control study enrolled 363 participants who were divided into two groups based on annual declines in MMSE score: 40 cases with an MMSE score decline of ≥0.5 points/year and 323 controls with maintained MMSE scores. Smoking, lower social functioning scores on the 36-Item Short Form Health Survey version 2, higher Pittsburgh Sleep Quality Index (PSQI) global scores, and sleep disorders were significantly associated with a decline in MMSE scores. Multivariate logistic regression analysis revealed higher age, current smoking status, and either higher PSQI global scores or sleep disorders to be independently associated with MMSE score decline. In conclusion, the present study identified aging, smoking, and sleep quality as factors associated with a greater decline in MMSE scores in cognitively healthy individuals. Our findings highlight the potential importance of lifestyle factors in preventing cognitive decline.