Older adults with reduced kidney function may be an increased risk of developing dementia, according to a large population-based study from Sweden. "Even a mild reduction in kidney function has been linked to an increased risk of cardiovascular disease and infections, and there is growing evidence of a relationship between the kidneys and the brain," Dr. Hong Xu of the Karolinska Institute, in Stockholm, said in a news release. Dr. Xu and colleagues analyzed the association of estimated glomerular filtration rate (eGFR) with the risk of dementia (defined as a new dementia diagnosis or initiation of dementia treatments) among more than 329,000 residents of Stockholm who were followed for an average of five years, were at least 65 years old and had no history of dementia or use of kidney-replacement therapy. During follow-up, 5.8% were diagnosed with dementia. As kidney function declined, the rate of dementia increased, the researchers report in Neurology. In people with a normal eGFR of 90 to 104 mL/minute, there were seven cases of dementia per 1,000 person-years. In contrast, in people with severe kidney disease (eGFR <30 mL/min), there were 30 cases of dementia per 1,000 person-years. After multivariable adjustment, people with moderate chronic kidney disease (eGFR 30 to 59 mL/min) had a 71% higher risk of developing dementia compared to those with normal kidney function (HR, 1.71; 95% confidence interval, 1.54 to 1.92) and people with severe kidney disease had a 162% higher risk (HR, 2.62; 95% CI, 1.91 to 3.58). In a subgroup of 205,622 people who had multiple blood tests over one year, the researchers found that a steeper decline in eGFR during this time frame was also associated with a higher risk of a dementia diagnosis later on. One in 10 dementia cases could be attributed to an eGFR of 60 mL per/min or less, which is a higher proportion of dementia cases than those attributed to other dementia risk factors like cardiovascular disease and diabetes, the researchers say. "Our study identifies chronic kidney disease as a possible risk factor for dementia, however while it shows an association, it does not prove that it is a cause," Dr. Xu said in the news release. "More research is needed to determine the exact reasons for the association. Still, our findings raise awareness of the link between these two conditions and may help health professionals develop and implement strategies to screen for kidney disease and monitor kidney function in people at risk of dementia. Identifying and treating cases sooner may reduce the risk of dementia," Dr. Xu added. Dr. Ankur Shah of the Division of Kidney Diseases and Hypertension at Warren Alpert Medical School of Brown University, in Providence, Rhode Island, said this study is "quite interesting" and is "strengthened particularly by the robust size and minimal loss to follow-up. The methodology is robust and the findings help bring clarity to a question that has had prior studies with conflicting outcomes." "As noted by the authors," he told Reuters Health by email, "the prior studies that have not shown a correlation between dementia and chronic kidney disease were limited in the number of individuals with kidney disease who enrolled. It should be noted that this study would need to be replicated in a prospective manner in order to better delineate causality over correlation." It's also not known if therapies that slow the decline of GFR will also decrease the incidence of dementia, Dr. Shah added. "This study answers an important question, but also raises new questions. As a clinician, these findings serve as reminder of the importance of multi-disciplinary care, and hopeful that future research may demonstrate interventions that can prevent cognitive decline," Dr. Shah added. The study was supported by the Swedish Research Council and Karolinska Institute. —Megan Brooks Source
