Association of low bone mineral density and dementia in older women: insights from the Longevity Improvement and Fair Evidence Study

Background: Both osteoporosis and dementia have emerged as important public health challenges in Japan's aging population. This study aimed to investigate the impact of low bone mineral density (BMD) on the subsequent risk of dementia in older Japanese women aged ≥65 years, given the overlapping demographics of individuals affected by these two conditions. Methods: This cohort study was conducted using osteoporosis screening data and insurance claims data from a municipality. We identified 8618 women (median age: 73 years) who underwent osteoporosis screening between April 2019 and March 2021. Participants with a BMD <80% of the young adult mean were assigned to a low-BMD group (n = 2297), whereas those with a BMD ≥80% were assigned to a control group (n = 6321). The study outcomes were new-onset all-cause dementia and Alzheimer's disease (AD). To estimate the risk of low BMD on these outcomes, we constructed Cox proportional hazards models that adjusted for covariates (age, care needs, year of cohort entry, comorbidities and medications) using inverse probability of treatment weighting. Results: The low-BMD group had a significantly higher risk of developing both all-cause dementia (adjusted hazard ratio: 1.58, 95% confidence interval: 1.20-2.08) and AD (1.61, 1.11-2.36) than the control group over approximately 30 months of follow-up. Conclusion: These findings suggest that low BMD is associated with medium-term onset of dementia. Osteoporosis screenings could be useful not only for the secondary prevention of osteoporosis, but also for the primary prevention of dementia.