Enhanced Cognitive Function And Alertness

Two recent double-blind studies have confirmed that guarana has significant effects on cognitive function and provide evidence that these effects are not just mediated by the herb's caffeine content (Haskell et al 2005, Kennedy et al 2004).

One double-blind, placebo-controlled study assessed the effects of four different doses of guarana (37.5, 75, 1 50 and 300 mg) in 22 subjects (Haskell et al 2005). Cognitive performance and mood were assessed at baseline and again 1, 3 and 6 hours after each dose using the Cognitive Drug Research computerised assessment battery, serial subtraction tasks, a sentence verification task and visual analogue mood scales. All doses improved picture and word recognition, results on the Bond-Lader visual analogue scales and caffeine research visual analogue scales showing improvements in alertness and reduced ratings of headache. The two lower doses produced better results than the two higher doses, which were associated with impaired accuracy of choice reaction and on one of the subtraction tests. Several observations suggest that these effects were not due to caffeine alone. Firstly, effects were still apparent 6 hours after administration and secondly, better results were obtained with a dose of 37.5 mg than 300 mg with a caffeine content of less than 5 mg in the lowest dose.

Another double-blind, placebo controlled study investigated the effects of a single dose of guarana (75 mg) on cognition, in combination with and in comparison to ginseng (Panax ginseng 200 mg) in 28 healthy volunteers (Kennedy et al 2004). Guarana was shown to produce comparable effects to ginseng in improved task performance with all three treatments better than placebo. However, guarana was superior to ginseng in improving the speed of performed tasks. Once again, given the low caffeine content (9 mg) of the guarana extract used in that study, the effects are unlikely to be attributable to its caffeine content alone, particularly as the dose was shown to be as effective as a 16-fold dose of pure caffeine.

Two previous randomised, double-blind studies have investigated the effects of guarana on cognitive function and produced negative results (Galduroz & Carlini 1994, 1996). One study involving 45 healthy elderly volunteers found that guarana treatment was ineffective (Galduroz & Carlini 1996), which confirmed the findings of a previous study conducted by the same authors (Galduroz & Carlini 1994). Studies in some animal models have produced positive results for both single-dose and long-term administration of guarana, observing a positive effect on memory acquisition and memory maintenance (Espinola et al 1997).

© 2007 Elsevier Australia

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