Physical and cognitive functioning of people older than 90 years: a comparison of two Danish cohorts born 10 years apart
The Lancet, 382:9903, 1507–1513 (2013)
Background. A rapidly increasing proportion of individuals in the Western world are surviving into their tenth decade. There is widespread concern that the basis for this development is the survival of frail and disabled elderly into the highest ages, the so-called "Failure of Success Hypothesis".
Methods. Two complete cohorts of Danish nonagenarians born ten years apart were assessed in their homes: the Danish 1905-Cohort at age 93 (N=2262), and the 1915-Cohort at age 95 (N=1584). All cohort members were eligible regardless of type of residence. The surveys used the same design and assessment instrument and had virtually identical response rates (63%). Cognitive functioning was assessed by Mini Mental State Examination (MMSE) and a cognitive composite of 5 tests sensitive to age-related changes. Physical functioning was assessed by an Activity of Daily Living score as well as by physical performance tests: grip strength, chair stand and gait speed.
Findings. The chance of surviving to age 93-95 was 30% higher in the 1915-Cohort than in the 1905-Cohort. Despite being two years older at assessment, the 1915-Cohort members scored significantly better on the MMSE (22.8 (SD=5.6)) than the 1905-Cohort (21.4 (6.0)) (P<0.001) and with a substantially higher proportion with maximum scores (28–30): 23% vs. 13% (p<0.001). Similarly, the cognitive composite score was significantly better (p<0.001) among the 1915-Cohort members. There were no consistent differences over cohorts in the physical performance tests for either sex, but the 1915-Cohort had significantly better Activity of Daily Living score than the 1905-Cohort.
Interpretation. The 1915-Cohort had better survival and scored significantly better on both the cognitive tests and the Activity of Daily Living scale than the 1905-Cohort, despite being two years older, indicating a "Success of Success" with more individuals living to higher ages with better overall functioning.
Keywords: Denmark, cohorts, health, morbidity, old age, surveys