Poor Cognitive Function Linked to Brain Hormone Levels
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, Dr. Daniels said. 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, atrial fibrillation that creates microemboli, microcirculation deficits that harm both the heart and brain, and genetic predisposition.
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 1997–1999 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, 41% were college graduates, 12% had diabetes, 6% had a history of stroke, and 20% a history of cardiovascular disease.
The researchers used three tests to evaluate cognitive function: The Mini-Mental State Exam (MMSE), which assessed cognitive features, including orientation, attention, calculation, and recall (a score of 24 or less indicated poor cognitive function); the Trail-Making Test B, which gauged executive function (a score of 132 seconds or more indicated poor function); and a category fluency test that asked participants to name as many animals as they could in 1 minute (a score of 12 or less indicated poor function).
MMSE results 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 cognitive function tests, compared with those who had low levels.
The next step in exploring the link between natriuretic peptide and cognitive function should be a prospective study, Dr. Daniels said.
She received research support from Roche Diagnostics, which markets an NT-proBNP assay.
Tests used to evaluate cognitive function included the MMSE and the Trail-Making Test B.
Source DR. DANIELS
