Impaired kidney function is associated with a more rapid rate of cognitive decline in old age, according to a new study (Neurology. 2009;73:920-927).

Previous attempts to link the two conditions have yielded conflicting results. Investigators sought to clarify the relationship using data from more than 850 older people (mean age 80.6 years) without dementia participating in the Rush Memory and Aging Project.

Over six years, poor kidney function was linked with a more rapid rate of decline in cognition in three specific areas: episodic memory, semantic memory, and working memory. However, perceptual speed and visuospatial abilities were not affected by declines in kidney function.

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The association persisted even after researchers excluded participants with severely impaired kidney function from analysis and accounted for several potential confounders.

“Until recently, less severe kidney dysfunction has not been considered a risk factor for cognitive impairment in the elderly,” the investigators point out.

Visuospatial abilities were not shown to be affected by changes in kidney function, but these skills may decline years prior to a clinical diagnosis of Alzheimer’s disease (Arch Neurol. 2009;66: 1254-1259). In a study of 444 initially dementia-free people, 134 developed dementia over an average follow-up of 5.9 years. “One novel finding was that visuospatial abilities demonstrated an inflection point three years before clinical diagnosis.”