A prospective study of albuminuria and cognitive function in older adults: the Rancho Bernardo study

Abstract

Chronic kidney disease is a risk factor for cognitive impairment. Albuminuria is an early manifestation of chronic kidney disease and a marker of endothelial dysfunction and vascular risk. Results of prior studies of albuminuria and cognitive function are contradictory. The authors studied 1,345 community-dwelling women and men in southern California (mean age, 75 years) at a 1992-1996 research clinic visit, when urine albumin/creatinine ratio (ACR) was measured in spot morning urine and cognitive function was evaluated by using the Mini-Mental State Examination Trail-Making Test B, and category fluency test. An ACR of > or =30 mg/g was found in 17% of women and 15% of men in 1992-1996. Analysis of covariance was used to compare cognitive function score by categorical ACR. Between 1999 and 2002, 759 participants returned for repeat cognitive function testing. For men, but not women, baseline albuminuria, but not estimated glomerular filtration rate, was associated with reduced cognitive function at follow-up on all tests (P's < 0.05). An ACR of > or =30 mg/g was associated with greater annual decline in Mini-Mental State Examination and category fluency scores. Albuminuria may be an easily measured marker predicting future cognitive function decline. Results imply a common underlying mechanism affecting the renal and cerebral microvasculature.

Figure 1.

Selection of participants for a study of albuminuria and cognitive function in older adults, Rancho Bernardo, California. In 1992–1996, 1,429 participants attended a research clinic visit and completed 3 cognitive function tests. After exclusion of 11 individuals without urine samples, 12 who were younger than age 50 years, and 61 with a history of stroke, 821 women and 524 men remained who had urine samples for albuminuria testing and tests of cognitive function in 1992–1996. Of these participants, 461 women and 298 men returned for a follow-up visit and had repeat cognitive function testing in 1999–2002.

Figure 2.

Prevalence (%) of impaired kidney function by estimated glomerular filtration rate (eGFR) and urine albumin/creatinine ratio (ACR) at the baseline research clinic visit in 1992–1996, Rancho Bernardo, California.

Figure 3.

Prevalence (%) of poor cognitive function—Mini-Mental State Examination (MMSE) score <24, Trail-Making Test B (Trails B) score ≥132, and category fluency test score <12—in 1992–1996 and 1999–2002, Rancho Bernardo, California.