Cognitive function constitutes a critical dimension of the health status of
elderly individuals. Age-associated decline in cognitive function may partly be
attributed to the negative effects of systemic medical diseases and related factors,
including cardiovascular diseases (CVDs) and vascular risk factors. Cognitive
decline has been an understudied outcome in cardiovascular epidemiological
research. Few reports have comprehensively examined cognitive function in relation
to clinical manifestations of systemic atherosclerotic disease in different arterial
beds. Inconsistent findings are common in the literature and these arc likely to reflect
the vast differences between studies regarding the choice of population under study,
the methods applied for measuring and defining CVD, the types and timing of
administration of protocols used for assessing cognitive function, and the paths taken
in the analysis of data.
The principal aim of the present study was to examine the longitudinal
change in cognitive test performance in relation to major clinical CVDs and vascular
risk factors in a population-based sample of older people. The administration of a
battery of neuropsychological tests on two separate occasions facilitated the study of
actual change in both general cognition and across different cognitive abilities
according to an objectively-determined CVD status. A valid estimation of peak prior
cognitive ability allowed the exploration of the impact of CVD and risk factors on
the imputed decline from best-ever level of cognitive function to that measured in old
age.
The analysis is based on a cohort of 809 men and 783 women aged 55-74
years which in 1987/8 was randomly selected from the general population of
Edinburgh. A comprehensive assessment of the prevalence of major CVDs and
vascular risk factors was held at baseline and during two follow-up examinations.
Since baseline, the study sample has been followed up to determine the incidence of
angina pectoris, peripheral arterial disease (PAD), myocardial infarction (MI), and
stroke. Cognitive testing was first held in 1998/9 when the mean age of the surviving
cohort (n=1209) was 73.1 years (SD=5.0) and subsequently about four years later
using the same test protocol. The present investigation is based on the 452 study
participants who attended follow-up cognitive testing in 2002/3.
Both general cognition, as indexed by a general cognitive factor representing
the variance common to all the cognitive tests used, and most individual cognitive
measures were negatively affected in participants with CVD but no evidence of
stroke relative to non-vascular controls. Of the specific CVD manifestations, stroke
was significantly associated with a steeper four-year decline in both general
cognitive function and verbal memory. When decline was estimated from peak, prior
cognitive level, stroke was related to a greater decline in both general cognition and
verbal fluency. In the absence of stroke, MI was associated with an accelerated fouryear
decline in non-verbal reasoning ability but the presence of angina was not
related to cognitive decline in this study. Symptomatic PAD also independently
predicted faster decline in both general cognition and verbal memory over the fouryear
follow-up. Several potentially modifiable vascular risk factors, including
education, body mass index, smoking, diastolic blood pressure, inflammatory
markers and blood viscosity were also related to decline in general and specific
cognitive abilities, independently of age, sex, prior cognitive ability and vascular
disease. The associations with decline in specific cognitive measures principally
resulted from the impact of atherosclerotic disease and risk factors on general
cognitive ability rather than the individual functions per se.
The findings from the present study further add to those of previous
investigations demonstrating a relationship between CVDs, vascular risk factors, and
cognitive decline in older people. Specifically, they reveal that, even in the absence
of overt stroke, clinical CVDs are associated with a greater cognitive decline in the
elderly, independently of potential confounding by a wide range of vascular risk
factors. Also, the relationships between several vascular risk factors and cognitive
decline proved to be independent of overt co-existing vascular pathology. Based on
these findings, further study is needed to determine the combined effects of CVDs
and multiple risk factors on cognitive outcomes in samples of older people. In
addition, what the likely pathological mechanisms are underlying cognitive decline
associated with atherosclerotic disease and vascular risk factors needs to be
addressed in future studies. From a perspective of preventing or delaying vascular
based cognitive decline and impairment, more research is required to assess the
effectiveness of both individual and population-based strategies targeting vascular
disease and risk factors in older age groups. Finally, further investigation is needed to
address the potential impact of subtle cognitive deficits on indicators of the quality of
life and the capability of self-maintenance of elderly vascular patients, on adherence
to medical treatment and rehabilitation, and further cognitive decrements and
survival.
