A new study published in the medical journal Neurology suggests that impaired kidney function is a risk factor for cognitive decline in old age.

The study, conducted by researchers at Rush University Medical Center, in Chicago, found that poor kidney function was linked specifically with cognition related to memory functions. Damage to one of these functions, episodic memory, which retrieves memories of time, place, associated emotions, and other contextual knowledge, is often the earliest sign of Alzheimer's disease.

"Given the dearth of modifiable risk factors for age-related cognitive decline, these results have important public health implications," says Dr. Aron Buchman, a neuroscientist in the Rush Alzheimer's Disease Center. "Further work to understand the link between kidney function and the brain may provide new strategies for preventing memory loss in elders."

Buchman says the findings suggest there are common disease processes that affect both the brain and the kidneys in the elderly, and hypothesizes that underlying vascular problems, such as diabetes and hypertension, may account for the association between kidney problems and cognitive decline.

The study analyzed data for nearly 900 older adults who participated in the Rush Memory and Aging Project, a group of community-dwelling seniors with a mean age of 81, all of them initially free of dementia. The participants were examined annually for up to six years to track changes in cognition over time. Cognitive assessments included multiple tests that were summarized as a composite measure of overall cognition and of five individual cognitive abilities.

The individual cognitive systems assessed were "visuospatial" ability; perceptual speed, or the ability to quickly and accurately compare letters, numbers, objects, pictures, or patterns; semantic memory, related to meaning, understanding, and other concept-based knowledge; working memory, which temporarily stores and manipulates information; and episodic memory.

Ruling out the influence of factors like aging and medications, which can affect cognition, the researchers found that poor kidney function, assessed at the beginning of the study, was linked with a more rapid rate of decline in cognition over the next several years—not in visuospatial ability or perceptual speed, but in three specific areas: episodic, semantic, and working memory.

The rate of decline in cognition was equivalent to that of a person seven years older at baseline, Buchman said.