In the study, researchers analyzed over 3,300 women aged 70 years or older from the Nurses’ Health Study who had repeated cognitive testing. The participants had repeated assessments of cognition administered by phone every two years, including tests for general cognition, verbal memory, verbal fluency, and working memory for up to six years of follow-up. Kidney dysfunction was defined as higher urinary albumin-to-creatinine ratio of > 5 mg/gm or plasma-creatinine based estimated glomerular filtration rate (eGFR) of < 60 ml/min/1.73m2.
The researchers found that a higher albumin/creatinine ratio (ACR) was significantly associated with two to seven times faster cognitive decline than that associated with each one year of aging alone in all four cognitive measures whereas eGFR was not. “The ACR levels associated with cognitive function decline are very low levels, which have not been traditionally considered clinically significant,” said lead study author Julie Lin, MD, MPH, FASN. “These findings are consistent with recent evidence suggesting that albuminuria at levels much lower than the generally accepted 30 mg/gm cutoff (widely used to define microalbuminuria) are also consistently and independently associated with risk for progression of kidney disease, cardiovascular disease, and all-cause mortality. We hypothesize that the albuminuria is a signal of early vascular disease in the brain, which leads to subsequent cognitive decline as it progresses.”
Because the prevalence of kidney disease and cognitive decline increases with advancing age, they are both important public health concerns in the aging U.S. population. Investigators hope that further research into the relationship between kidney dysfunction and cognitive decline may elucidate physiologic pathways linking these conditions that in turn, will help identify new treatment options for cognitive decline.
The study was funded by a research grant from the National Institutes of Health (NIH).