Guarana (Paullinia cupana) and Memory: evidence and sources

The plant extract guarana is known for its caffeine content and other bioactive ingredients, which purportedly may improve cognitive performance. Recent reviews have examined the effects of chronic supplementation of guarana in clinical populations; however, the acute effects of guarana on cognitive tasks, while of interest, have produced mixed results. Whether acute guarana ingestion improves human cognitive performance was assessed by performing a systematic review coupled with a meta-analysis. Eight placebo-controlled studies were identified and met the inclusion criteria providing data on 328 participants. The dose of guarana (37.5 to 500 mg) with reported caffeine content (4.3 to 100 mg) varied. Effect sizes (ESs) were calculated as the standardized mean difference and meta-analyses were completed using a random-effects model. The ESs for guarana averaged across a variety of cognitive measures and outcome variables were less than trivial (Hedge’s g = 0.076, p = 0.14). Using a subgroup meta-analysis (Q = 12.9, p < 0.001), ESs indicating a faster response time for guarana vs. a placebo (g = 0.202, p = 0.005) differed from the accuracy measures (g = −0.077, p = 0.4) which were non-significant. For response time, guarana ingested in a capsule (g = 0.111) tended to differ (Q = 2.96, p = 0.085) compared to guarana when dissolved in liquid (g = 0.281). Meta-regression of the study ESs of overall cognitive task performance was not related to the guarana dose (R2 < 0.001) or to the time allowed prior to cognitive testing (R2 < 0.001). Acute guarana ingestion had a small effect on the response time (faster performance) during a variety of cognitive tasks without affecting the accuracy. Whether the changes were linked to the caffeine content or other bioavailable substances in guarana is unknown. Additional studies that directly compare matched doses of caffeine versus guarana are needed to understand its effects on cognitive performance.

The present study aimed to systematically assess acute, dose-related behavioural effects of an extract of guaraná plant for the first time in humans. This double-blind, counterbalanced, placebo-controlled study (n=26) assessed the acute mood and cognitive effects throughout the day of four different doses (37.5 mg, 75 mg, 150 mg and 300 mg) of a standardised guaraná extract (PC-102). Assessment included the Cognitive Drug Research computerized test battery and Bond-Lader mood scales. Guaraná improved secondary memory performance and increased alert and content mood ratings. The two lower doses produced more positive cognitive effects than the higher doses. This research supports previous findings of cognitive improvements following 75 mg guaraná and provides the first exploration of different dose effects of guaraná in humans. The findings suggest that the effects cannot be attributed to caffeine alone.

Alzheimer disease (AD) is a progressive neurodegenerative brain disorder that causes significant disruption in normal brain functioning, representing the most common cause of dementia in the elderly. The main hallmark of AD is the presence of amyloid plaques in the brain formed by the deposition of insoluble amyloid protein (Aβ) outside of neurons. Despite intensive investigation of the mechanisms of AD pathogenesis during the past three decades, little has been achieved in terms of effective treatments or ways to prevent the disease. Paullinia cupana , known as guarana, is a plant endemic to the Amazon region in Brazil with several beneficial effects reported, including delayed aging. In this study, we investigated the effects of chronic consumption of guarana ethanolic extract (GEE) on Aβ toxicity using a C. elegans model of AD. We analyzed the behavioral phenotype, oxidative damage and Aβ protein expression in worms treated with GEE. In addition, we investigated the possible role of the heat shock response on the beneficial effects induced by GEE. Overall, our data demonstrate that chronic GEE treatment decreased the formation of Aβ aggregates in C. elegans , preventing the behavioral deficits and the oxidative damage inducible by Aβ expression, due to activation of the heat shock protein (HSP) response. This finding provides a new alternative against amyloidogenic neurodegenerative diseases and other diseases caused by protein accumulation during aging.