Cognitive and kidney function: results from a British birth cohort reaching retirement age.
BACKGROUND
Previous studies have found associations between cognitive function and chronic kidney disease. We aimed to explore possible explanations for this association in the Medical Research Council National Survey of Health and Development, a prospective birth cohort representative of the general British population.


METHODS
Cognitive function at age 60-64 years was quantified using five measures (verbal memory, letter search speed and accuracy, simple and choice reaction times) and glomerular filtration rate (eGFR) at the same age was estimated using cystatin C. The cross-sectional association between cognitive function and eGFR was adjusted for background confounding factors (socioeconomic position, educational attainment), prior cognition, and potential explanations for any remaining association (smoking, diabetes, hypertension, inflammation, obesity).


RESULTS
Data on all the analysis variables were available for 1306-1320 study members (depending on cognitive measure). Verbal memory and simple and choice reaction times were strongly associated with eGFR. For example, the lowest quartile of verbal memory corresponded to a 4.1 (95% confidence interval 2.0, 6.2) ml/min/1.73 m(2) lower eGFR relative to the highest quartile. Some of this association was explained by confounding due to socioeconomic factors, but very little of it by prior cognition. Smoking, diabetes, hypertension, inflammation and obesity explained some but not all of the remaining association.


CONCLUSIONS
These analyses support the notion of a shared pathophysiology of impaired cognitive and kidney function at older age, which precedes clinical disease. The implications of these findings for clinical care and research are important and under-recognised, though further confirmatory studies are required.
Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, United Kingdom.
Richard J
RJ
Silverwood
MRC Unit for Lifelong Health and Ageing, University College London, London, United Kingdom.
Marcus
M
Richards
MRC Unit for Lifelong Health and Ageing, University College London, London, United Kingdom.
Mary
M
Pierce
MRC Unit for Lifelong Health and Ageing, University College London, London, United Kingdom.
Rebecca
R
Hardy
BHF Glasgow Cardiovascular Research Centre, University of Glasgow, Glasgow, United Kingdom.
Naveed
N
Sattar
Department of Renal Medicine, Queen Elizabeth Hospital, Birmingham, United Kingdom.
Charles
C
Ferro
School of Immunity and Infection, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom.
Caroline
C
Savage
MRC Unit for Lifelong Health and Ageing, University College London, London, United Kingdom.
Diana
D
Kuh
Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, United Kingdom.
Dorothea
D
Nitsch
D003071:Cognition; D003072:Cognition Disorders / Q000150:complications / Q000175:diagnosis / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D051436:Renal Insufficiency, Chronic / Q000150:complications / Q000175:diagnosis / Q000453:epidemiology*; D012179:Retirement; D012959:Socioeconomic Factors; D006113:United Kingdom / Q000453:epidemiology