Incidence of dementia in the oldest-old and its relationship with age: The Monzino 80-plus population-based study

Introduction: Relationship between age and dementia at extreme old ages is still an open question, yet population-based studies in this high-risk age segment are rare. Methods: The Monzino 80-plus is a population-based study among residents 80 years and older in the Varese province, Italy. Of 1371 eligible individuals, 1294 (94.4%), of whom 64 are centenarians, were included in the incidence study. Results: Since 2002, 584 new cases of all-cause dementia were identified over 15 years. The overall incidence rate was 7.9 per 100 person-years. Dementia risk rose with age (IRR: 1.06), with the cubic model providing the best fit (R-2 = 0.91-0.96). Cumulative incidences of dementia unadjusted and adjusted for competing mortality risk progressively diverged with age. Conclusion: Dementia incidence also keeps rising in nonagenarians and centenarians. Slowing down in growing risk of developing dementia with age is mainly attributable to increasing competing risk of death and resulting selective survival of individuals at lower risk of dementia.