08.07.2013
by Charles Bankhead
Staff Writer, MedPage Today

Older people with impaired neurovascular coupling at baseline who drank two cups of cocoa a day for a month had significant improvement in cognitive function and blood flow in the brain, investigators reported.

Among patients with impaired neurovascular coupling (NVC, a measure of cerebral blood flow), performance on a test of cognitive function improved by 30%, which was associated with more than a two-fold increase in NVC. Patients with intact NVC showed no such improvements between baseline and day 30.

Flavanol enrichment of the cocoa did not significantly improve any outcome measures,Farzaneh A. Sorond, MD, PhD, of Brigham and Women’s Hospital in Boston, and co-authors reported online in Neurology.

“There is a strong correlation between neurovascular coupling and cognitive function, and both can be improved by regular cocoa consumption in individuals with baseline impairments,” the authors concluded. “Better neurovascular coupling is also associated with greater white matter structural integrity.”

The results add to a strong biological rationale for favorable health effects of flavonoid-rich foods, which include chocolate.

“Previous work has demonstrated the antioxidant benefits of flavonoids in chocolate and other foods,” said Gary W. Small, MD, of the University of California Los Angeles, who was not involved in the study. “This well-designed, placebo-controlled trial offers new findings in that it links neurovascular coupling, a measure of brain blood flow and neural activity, to improved cognitive abilities in people consuming a popular flavonoid-rich food, cocoa.”

NVC refers to the spatial relationship between neuronal activity and cerebral blood flow, and impaired NVC has a strong association with brain pathology. Studies involving preclinical models have shown that impaired NVC plays a role in several types of human disease.

The relationship between NVC and cognitive function has remained unclear, the authors noted, as has NVC’s relationship with structural changes in brain tissue that occur with aging and vascular disease. Sorond and colleagues designed a study to examine the issues in older people with vascular disease.

The study had three principal objectives: to determine whether lower cerebral blood flow (impaired NVC) in response to a task translates into lower cognitive performance, examine the relationship between impaired NVC and cerebral white matter disease, and determine whether flavanol-enriched cocoa had an effect on NVC. The authors noted that flavanols have been shown to improve endothelial function and cognitive performance.

The investigators enrolled 60 healthy volunteers older than 65 (mean age 72.9) who had hypertension or well-controlled type 2 diabetes. They excluded people who had absent temporal acoustic windows, intracranial stenosis, stage II hypertension poorly controlled by medication (>160/100 mm Hg), serum creatinine >2 mg/dL, dementia, or a history of stroke, chest pain, or heart attack within the past 6 months.

Participants’ cerebral blood flow velocity was measured before and after a 30-day trial of a flavanol-enriched or flavanol-poor cocoa drink. Evaluations occurred on days one, two, and 30. Each assessment included measurement of participants’ blood pressure, transcranial Doppler, and evaluation of cognitive function by the Mini-Mental State Examination (MMSE) and Trail Making Tests A and B.

A subgroup of 24 patients underwent MRI imaging for measurement of normal and abnormal white-matter volumes and tissue microstructure in white-matter volumes.

Participants were randomized to either the flavanol-enriched or flavanol-poor cocoa, which they mixed with water and drank twice a day. They continued existing medications but were encouraged to change their diet to account for the calories in the cocoa and to avoid other forms of chocolate during the study, as well as caffeine on the three assessment days.

A preliminary analysis of data showed no significant differences in outcomes by the flavanol status of the cocoa, so the investigators combined the groups for comparisons of baseline values and those at follow-up.

The results showed that NVC had a significant association with Trails B scores (P=0.002) and with responses in the middle cerebral arteries to the cognitive tasks. The 41 participants with intact NVC had a mean reaction time of 89 seconds versus 167 seconds for the 17 individuals with impaired NVC (<5% at baseline).

In general, NVC had an inverse association with white matter macro- and microstructural damage. Participants with intact NVC had greater volumes of normal white matter and smaller abnormal volumes.

Response to cocoa differed significantly by NVC status. Sorond and colleagues reported that 89% of participants with impaired NVC responded to cocoa consumption (increased NVC) as compared with 36% of participants who had intact NVC at baseline (P=0.0002).

Participants with impaired NVC had a 10.6% improvement after 24 hours and 8.3% at 30 days (P<0.0001 for both comparisons). In contrast, those with normal baseline coupling had responses of -1.5% at 24 hours and -2.0% at 30 days.

Additionally, participants with impaired NVC had significant improvement in Trails B performance at 30 days (P=0.007) versus no significant change in the people with intact NVC at baseline.

The results suggest that regular cocoa consumption might represent a viable strategy to reduce or even reverse cerebral vascular pathology, said the authors of an accompanying editorial.

“Sorond et al demonstrate a convincing link among cerebral vascular function, structural integrity of the brain, and cognitive function, and showcase the remarkable potential for transcranial Doppler ultrasonography as a biomarker for cerebral vascular pathology,” said Paul B. Rosenberg, MD, of Johns Hopkins, and Can Ozan Tan, PhD, of Harvard.

“While the authors did not find a difference in NVC or cognitive measures between the two treatment arms … cocoa consumption improved NVC, as well as cognitive performance, in participants with impaired baseline neurovascular coupling.”

• Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

LAST UPDATED 08.08.2013