ORLANDO — High blood levels of a brain natriuretic peptide were associated with poor cognitive function in a study of 950 community-dwelling, healthy, elderly adults.
“This is the first time this [association] has been shown,” Dr. Lori B. Daniels said at the annual scientific sessions of the American Heart Association.
Elevated levels of natriuretic peptide mark the presence of a variety of disease states, especially heart failure, said Dr. Daniels. She suggested several mechanisms that might link production of natriuretic peptide to poor cognitive function, including reduced cardiac output that drops oxygen or nutrient supplies to the brain and atrial fibrillation that creates microemboli.
Another issue is “which comes first, cardiovascular disease or poor cognitive performance,” said Dr. Daniels, a cardiologist at the University of California, San Diego.
Patients analyzed were enrolled in the Rancho Bernardo study in the early 1970s. Of the more than 5,000 community-dwelling adults in the study, 950 underwent a battery of cognitive function tests from 1997 to 1999 and had blood specimens drawn; they were the focus of the new analysis.
The average age of the 950 participants was 77 years; 61% were women. Two-thirds were hypertensive, 4% were current smokers, 49% drank three or more alcoholic drinks per week, and 6% had a history of stroke.
The researchers used three tests to evaluate cognitive function: the Mini-Mental State Exam (MMSE), which assessed features such as orientation, attention, and recall; the Trail-Making Test B, which gauged executive function; and a category fluency test that asked participants to name as many animals as they could in 1 minute.
The MMSE identified poor function in 7%, the trail-making test B identified poor function in 30%, and category fluency identified poor function in 15%.
Natriuretic peptide levels in the blood specimens were measured using a test that detects N-terminal pro-B-type natriuretic peptide (NT-proBNP). Natriuretic peptide measurements were considered low if the level was less than 450 pg/mL, and high if the level was 450 pg/mL or greater. Among the 950 participants, 79% had a low level and 21% had a high level.
People with high levels of NT-proBNP had significantly worse results in all three tests, compared with those who had low levels. In the low level group, poor cognitive scores occurred in 5%, 23%, and 12% of subjects for the three cognitive function tests, respectively. In the high level group, 17%, 54%, and 26% of the subjects scored poorly on the three tests, respectively.
When the results were adjusted for age, education, body mass index, exercise, alcohol use, and smoking, participants with high NT-proBNP levels had significantly worse cognitive function scores on the MMSE and the Trail-Making Test B. Poor scores for category fluency were lower in people with high NT-proBNP in the fully-adjusted model, but the difference fell short of statistical significance relative to those with low NT-proBNP.
Dr. Daniels received research support from Roche Diagnostics, which markets an NT-proBNP assay.