Somatic chronic diseases and 6-year change in cognitive functioning among older persons

Abstract

The influence of seven highly prevalent somatic chronic diseases on changes in cognitive functioning is investigated in older persons in a prospective design covering a 6-year follow-up period. The data were collected as part of the Longitudinal Aging Study Amsterdam (LASA). The associations between chronic diseases and cognitive functioning during 6 years of follow-up were analyzed among 1358 respondents (age 62–85) using generalized estimated equations (GEE). Cognitive tests were used to assess: general cognitive functioning, fluid intelligence, information processing speed and memory performance. In the fully adjusted models diabetes mellitus, stroke and peripheral artherosclerosis were associated with cognitive decline during a 6-year follow-up period in older persons. In the unadjusted models cardiac disease was negatively associated with memory function. However, after the correction for possible confounders this association became positive. Cancer was also associated with better memory function. A faster decline in especially memory function was found for diabetes mellitus, stroke, cancer, and peripheral artherosclerosis. The study shows that in older persons specific chronic diseases (diabetes mellitus, stroke, cancer, and peripheral artherosclerosis) are associated with decline in one or more domains of cognitive functioning during a 6-year follow-up period. These findings further stress that careful clinical evaluation of cognitive functioning in older persons with these diseases is required in order to provide adequate care.

Introduction

Aging is generally associated with an increasing prevalence of somatic chronic diseases as well as cognitive decline. Understanding the influence of chronic diseases in the context of its co-morbidity on cognitive functioning is important, because in old age, cognitive deficits may easily be misattributed to an early stage of dementia. Previously, the association between several specific chronic diseases and cognitive decline has been investigated extensively. Although this research has occasionally produced equivocal findings, most studies indicate a positive association between cognitive decline and cardiovascular (Di Carlo et al., 2000, Elwood et al., 2002, Van Exel et al., 2002), peripheral vascular (Elwood et al., 2002) and cerebro-vascular diseases (Jelicic and Kempen, 1997, Kase et al., 1998, Di Carlo et al., 2000, Dik et al., 2000), diabetes mellitus (Elias et al., 1997, Van Boxtel et al., 1998, Gregg et al., 2000, Arvanitakis et al., 2004, Logroscino et al., 2004), chronic obstructive pulmonary disease (COPD) (Jelicic and Kempen, 1997, Incalzi et al., 1998, Kozora and Make, 2000) and cancer (Meyers et al., 2000, Sjogren et al., 2000, Schagen et al., 2001). Most of these studies have been performed from an etiological or mechanistic viewpoint. Therefore, persons with co-morbid diseases are excluded from participation in order to investigate the association between a specific disease and cognitive decline. However, in old age, 50% of persons suffer from two or more chronic diseases (Haley, 1996), therefore investigating chronic diseases in persons with only one disease does not provide a realistic picture (Patrick et al., 2002). The relevance of this issue has been demonstrated in two studies that have shown that co-morbid diseases were associated with more serious cognitive decline than single diseases (Patrick et al., 2002, Hassing et al., 2004). Furthermore, most of the studies, which did take into account co-morbidity, used a cross-sectional study design, despite the fact that the influence of chronic disease on cognitive decline is best studied using a longitudinal design. Finally, in studying the association between somatic chronic diseases and cognitive decline in older persons, it is also important to take into consideration other concomitant risk factors for cognitive decline, such as old age, depression, vision or hearing impairment and the use of benzodiazepines.

Therefore, in the present study the association between specific chronic diseases and cognitive decline is investigated in the context of co-morbidity with other diseases. A longitudinal study design is employed, taking into account other concomitant risk factors for cognitive decline.