Cognitive function and blood rheology: results from the Caerphilly cohort of older men

Objectives: vascular lesions are important contributors to cerebral disease , yet relatively little work has been done on relationships between haemato logical factors and cognitive function. We have explored these relationship s in the Caerphilly cohort of older men. Design: the development of vascular disease and the decline in cognitive fu nction are being studied in a cohort of older men in Caerphilly, South Wale s, UK. We have recorded a range of life-style, dietary, lipid, haematologic al and theological factors which are, or may be, predictive of vascular dis ease. We have examined the relationships between these and both incident my ocardial infarction and stroke, and identified factors relevant to cognitiv e function. Setting: a community-based study based upon a representative population sam ple of older men. We collected data for the study from around 90% of the su rvivors of the original cohort. Subjects: 2154 men who were aged 55-69 years at the time blood was taken fo r the haematological tests and cognitive function was tested. Main outcome measures: we present data from the AH4 test of general cogniti ve performance and from choice reaction time, a test of vigilance. Results: there is a U-shaped relationship between haematocrit and cognitive function, the best cognitive function scores occurring at a mean haematocr it of 0.46. The relationship is significant for the choice reaction time (P < 0.05). The relationship between haematocrit and the AH4 test score is al so curvilinear, but it is not significant. Plasma viscosity showed strong a nd robust relationships, with significantly better cognitive performance an d faster reaction times at lower levels of viscosity (both relationships P < 0.001). Plasma fibrinogen concentration did not show any significant rela tionships with cognitive function. W these relationships are present, but a re much weaker, with rheological tests that had been carried out 5 years be fore the cognitive testing. Conclusions: blood theology, as estimated by both haematocrit and plasma vi scosity, is a significant determinant of cognitive function in older men. O n the other hand, the thrombotic potential of blood, as indicated by fibrin ogen level, shows no significant relationships. The relationships with theo logy seem to be direct, presumably through blood flow at the time of testin g, rather than through underlying long-term disease processes.