¹ Public Health Sciences, Centre for Population Health Sciences, University of Edinburgh, Edinburgh, UK
² Department of Psychology, University of Edinburgh, Edinburgh, UK
³ Division of Cardiovascular and Medical Sciences, Medical Faculty, University of Glasgow, Glasgow, UK
⁴ Department of Medicine, Royal Infirmary, Glasgow, UK

Introduction: vascular risk factors and diseases can negatively impact cognitive function. Determinants of blood flow are implicated in thrombogenesis and ischaemic events, yet little is known about their relationship with cognition.

Methods: blood rheology data were collected in 1987/88, and cognitive testing was performed in 1998/99 when the mean (±standard deviation) age of the study sample was 73.1 years (±5.0). Follow-up assessment was performed 4 years later. Information was collected on verbal declarative memory, non-verbal reasoning, verbal fluency, information processing speed and a general cognitive factor representing the variance common to the individual test scores.

Results: after controlling for age, sex and cognitive performance in 1998/99, blood viscosity (BV) (P < 0.05) and fibrinogen (P < 0.05) predicted decline in non-verbal reasoning over 4 years. When estimated from pre-morbid level, decline in general cognition (P < 0.05), non-verbal reasoning (P < 0.05) and information processing speed (P < 0.01) was associated with BV levels. Haematocrit (HCT) had similar effects (P < 0.01 to P < 0.001). All associations persisted after control for multiple confounders. When examined together, HCT but not BV independently predicted cognitive decline.

Conclusions: blood rheology is independently related to cognitive decline in older people. The value of strategies aimed at preserving cognition through influencing blood rheology needs investigation.

Keywords: haemorheology, blood viscosity, haematocrit, cognition, aged, elderly