Social isolation nearly tripled mortality risk among 3,024 Japanese adults aged 75 and older, with isolated individuals showing 2.37 times higher death rates over a mean 2.47-year follow-up period. The study tracked community-dwelling residents from Zentsuji City between 2020-2024, defining isolation as absence of regular family or friend contact. Isolated participants were typically older, exercised less, reported worse health and life satisfaction, and lived alone. This finding carries particular weight given Japan's status as having the world's longest life expectancy, suggesting social connections may be as crucial as medical care for longevity. The magnitude of risk—comparable to major cardiovascular risk factors—underscores isolation as a serious public health concern in aging societies globally. However, the relatively short follow-up period and observational design limit causal inferences. As populations worldwide age rapidly, these results highlight urgent need for community interventions targeting social connectivity among the oldest adults. Since this remains a preprint awaiting peer review, the specific risk estimates may change, but the pattern aligns with mounting evidence that social bonds are fundamental to healthy aging and survival.