Age Trajectory of High Cognitive Functioning Among the Oldest Old

The chance of reaching age 90 years has increased markedly over the last 50 years, and this chance will probably continue to increase with successive cohorts. There is a widespread concern that a large fraction of the future oldest old will be cognitively impaired. However, there is strong evidence that later born cohorts may have better late-life cognitive function than earlier born cohorts as studies have shown a decline both in the prevalence and in the incidence of dementia.

Cognitive functioning generally declines after the age of 40 years at an individual level, but there are substantial individual differences. This decline of cognitive functioning at an individual level may suggest that cognitive function at a population level decreases with age. However, in the Danish 1905 cohort, the age trajectory of both average and high cognitive functioning is constant at a population level from the age of 93 to 100 years because of higher mortality among those with the lowest cognitive scores. This suggests that currently in Denmark, exceptional longevity is not associated with high levels of cognitive impairment. It is, however, important to test whether this holds for more recent Danish cohorts and whether it applies to other countries as well. Furthermore, there is a need for a development of methodology for studies of the oldest old to address bias because of nonparticipation and dropout.