Trends Over Time in Cognitive Function and Activities of Daily Living Among Danish Centenarians.

Because of substantial improvements in old age mortality rates, oldest old and centenarians are the fastest growing age segments in modern time. Because aging, in general, is followed by an increased risk of physical and mental impairments and cognitive health, an increased number of these very old age groups may become a challenge to societies. However, improved survival may reflect health improvements among oldest old. This chapter reviews the present literature on cohort differences in cognitive impairment and activities of daily living (ADL) in older people, with an emphasis on oldest old and centenarians. Previous studies among older people suggest improvements in both ADL ("compression of disability") and cognitive function, whereas comparative studies of oldest old and centenarian birth cohorts show improvements in the most recent cohort with respect to the ability to carry out ADL but stable cognitive function. Cohort differences are highly influenced by changes in the incidence and prevalence of predisposing risk factors for cognitive impairment in an aging society, and these factors are addressed. Studying representative samples of the oldest old and centenarians entails methodological challenges in identification and a possible selection bias toward the better performing individuals. Although the present literature suggests that recent cohorts of female centenarians, but not male, perform better in ADL, although cognitive function is stable, further studies are needed to further understand the consequences of declining oldest old mortality rates in different low-mortality countries. Is the decline in mortality followed by a parallel decline in morbidity and disability supported by improvements in prevention and active treatment, or do the same improvements just extend life so that even the frailest survive into very old age leading to a rise in the prevalence of oldest old and centenarians with cognitive and physical impairment? Comparative cross-national studies in countries with low old age mortality and using ex ante harmonized questionnaires in well- defined populations is currently being carried out, and the results will add to our knowledge of whether or not there is a trade-off between low mortality and high disability and morbidity. [ABSTRACT FROM AUTHOR]