Is the association between late-life morbidity and disability attenuated over time? : Exploring the dynamic equilibrium of morbidity hypothesis

Context: There is evidence suggesting that the prevalence of disability in late life has declined over time while the prevalence of disabling chronic diseases has increased. The dynamic equilibrium of morbidity hypothesis suggests that these seemingly contradictory trends are due to the attenuation of the morbidity-disability link over time. The aim of this study was to empirically test this assumption.Methods: Data were drawn from three repeated cross-sections of SWEOLD, a population-based survey among the Swedish men and women ages 77 and older. Logistic regression models were fitted to assess the trends in the prevalence of Activities of Daily Living (ADL) disability, Instrumental ADL (IADL) disability, and selected groups of chronic conditions. The changes in the associations between chronic conditions and disabilities were examined in both multiplicative and additive models.Results: Between 1992 and 2011, the odds of ADL disability significantly declined among women whereas the odds of IADL disability significantly declined among men. During the same period, the prevalence of most chronic morbidities including multimorbidity went up. Significant attenuations of the morbidity-disability associations were found for cardiovascular diseases, metabolic disorders, poor lung function, psychological distress, and multimorbidity.Conclusion: In agreement with the dynamic equilibrium hypothesis, this study concludes that the associations between chronic conditions and disability among the Swedish older adults have largely waned over time.

Pulse Pressure magnifies the effect of COMT Val158Met on 15 Year Episodic Memory Trajectories

We investigated whether a physiological marker of cardiovascular health, pulse pressure (PP), and age magnified the effect of the functional COMT Val158Met (rs4680) polymorphism on 15-years cognitive trajectories [episodic memory (EM), visuospatial ability, and semantic memory] using data from 1585 non-demented adults from the Betula study. A multiple-group latent growth curve model was specified to gauge individual differences in change, and average trends therein. The allelic variants showed negligible differences across the cognitive markers in average trends. The older portion of the sample selectively age-magnified the effects of Val158Met on EM changes, resulting in greater decline in Val compared to homozygote Met carriers. This effect was attenuated by statistical control for PP. Further, PP moderated the effects of COMT on 15-years EM trajectories, resulting in greater decline in Val carriers, even after accounting for the confounding effects of sex, education, cardiovascular diseases (diabetes, stroke, and hypertension), and chronological age, controlled for practice gains. The effect was still present after excluding individuals with a history of cardiovascular diseases. The effects of cognitive change were not moderated by any other covariates. This report underscores the importance of addressing synergistic effects in normal cognitive aging, as the addition thereof may place healthy individuals at greater risk for memory decline.