Long-term social isolation speeds cognitive decline in older adults. Effect holds regardless of loneliness feelings. Study analyzed 30,000 people with 137,000 cognitive tests from 2004-2018. Fewer social contacts link to faster drops in concentration, memory, and thinking. Phenomenon independent of sex, education, or ethnic origin. 25% of over-65s were socially isolated pre-2019. Reducing isolation protects cognitive function across all groups. Regular social interactions slow brain aging processes. Social prevention equals medical prevention for dementia risk. Isolation rises with more solo-living seniors. No cure for Alzheimer's makes social ties crucial. UK scientists from St Andrews led the study. Published in The Journals of Gerontology. Effect visible over long-term tracking. Building social opportunities is public health priority. Holiday family time highlights interaction benefits.