A five-year Johns Hopkins University study of 715 older adults reveals that lower spinal bone mineral density, measured automatically by AI on routine chest CT scans, is linked to a 12.8% faster annual accumulation of regional white matter brain damage and steeper cognitive decline. While weak bones do not directly cause dementia, the findings highlight shared metabolic aging pathways amplified by diabetes and offer a low-cost, opportunistic screening tool to flag at-risk patients early.