Determinants and trajectories of healthy life expectancy and deficit accumulation in older adults in Germany - follow-up of the KORA-Age cohort study

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Increasing life expectancy combined with slowing birth rates will be an organizational and financial challenge if this increases the share of persons in the population living longer periods of time with chronic disease. Empirical evidence regarding the compression or extension of morbidity is still ambivalent. Healthy life expectancy (HLE) varies largely across countries, with Germany being below the European average. Here, estimates are ambiguous across gender and age strata and birth cohorts. Heterogeneity in healthy life expectancy can be due to the influence of critical (pre-, peri-post-war) life periods or to the gradual deterioration of functional status over the life span, i.e. deficit accumulation (DA). We therefore propose to study determinants of HLE in a representative sample of the aged German population, taking early life experience as a consequence of birth cohort and DA into account. We plan to use the well-established KORA (Cooperative Health Research in the Region of Augsburg) platform for a new data collection, and to use our already existing data from the KORA-Age cohort. We plan to examine HLE and DA as a function of birth cohort and sex in the KORA Age cohort, and to examine the association of DA with mortality. Since 1984 four cross-sectional population based studies, the KORA surveys S1 to S4, were conducted in Augsburg, Germany, and two surrounding counties. The KORA-Age cohort includes all participants from those KORA surveys aged 65 years or older at the end of 2008, i.e. born in or before 1943. The baseline study of KORA-Age took place in 2009. The proposed cohort study will be carried out as a 7-year re-assessment of estimated 2500 participants of the KORA-Age baseline study. Participants will be aged 73 to 96 years in 2015/2016 (older subgroup, stratum I). Additionally, the younger participants from the KORA surveys who were not yet 65 at the end of 2008 and thus not eligible for KORA-Age baseline but will be 65 to 72 at the end of 2015 will be included as an age- and sex-stratified sample of all KORA S1-S4 participants (i.e. born from 1944 to 1950, younger subgroup, stratum II). All information will be obtained by means of a postal health follow-up with a short health questionnaire and a telephone interview. Health expectancy will be defined as the time spent in different health states until death. As summary measure for DA, a Deficit Accumulation Index (DAI) will be constructed according to a well-defined procedure. The DAI will contain signs and symptoms, diseases, functional impairments and activity restrictions. Multivariable log-linear, mixed-effects and Cox regression models will be fitted to the data. Including a wide span of birth cohorts with longitudinal follow-ups should make it possible to disentangle the mechanisms that lead to a compression or extension of morbidity, separating age, period, and cohort effects.