Kidney decline linked to cognitive impairment

By Anthony J. Brown, MD

NEW YORK (Reuters Health) - In older adults, mental abilities seem decline as kidney function drops, according to the results of two new studies.

"It has long been known that advanced renal disease (i.e., dialysis) is associated with dementia or declining cognitive function," Dr. Joshua I. Barzilay, lead author of the first study, told Reuters Health. "More recently it has been demonstrated that early renal disease ... can also be associated with cognitive decline."

Barzilay, a physician with Kaiser Permanente of Georgia in Tucker, and his colleagues report their findings in the American Journal of Kidney Diseases.

The study involved 2316 subjects who participated in the Cardiovascular Health Cognition Study and had their renal function tested based on levels of protein in urine.

Overall, 12 percent of subjects had dementia, 15 percent had mild cognitive impairment, and 73 percent had normal cognitive function, the report indicates.

A doubling of urine protein levels, indicating worse kidneys function, increased the likelihood of dementia by 22 percent, the report indicates. After adjusting for other factors linked to mental impairment, the risk fell to 12 percent, which was still statistically significant.

The second study, in the same medical journal, involved 23,405 subjects who had kidney function and cognitive function assessed.

Chronic kidney disease was associated with cognitive impairment, increasing the odds by 23 percent regardless of other risk factors, Dr. Manjula Kurella Tamura, from the University of California in San Francisco, and colleagues found.

"The findings in both of these population-based studies are important," Dr. Daniel E. Weiner, from Tufts Medical Center in Boston, writes in a related editorial. "The implications, both for screening for cognition impairment as well as for care of individuals with chronic kidney disease, are notable."

SOURCE: American Journal of Kidney Diseases, August 2008.