Guarana: benefits, dosage, contraindications

Neurological

Although the effects of guarana on the central nervous system (CNS) have not been the subject of clinical studies, considerable evidence shows that caffeine, the main constituent of guarana, stimulates the CNS. Possible mechanisms include blockade of adenosine receptors and inhibition of phosphodiesterase. By blocking adenosine receptors, caffeine would increase the release of neurotransmitters such as dopamine. This could result in a reduction in the clinical expression of Parkinson's disease. It has also been proposed that caffeine may decrease GABA and serotonin signaling. The stimulating effects of caffeine on the CNS are thought to improve alertness and psychomotor performance. Caffeine increases plasma catecholamine levels, probably via antagonism of adenosine receptors and a reduction in extraneuronal uptake of catecholamines. In a small randomized, single-blind, placebo-controlled clinical trial, 15 subjects (normal sleepers) received 250 ml of a guarana seed beverage (500 mg of guarana seed powder in 100 ml) or a placebo. After a night of sleep restricted to 4 hours, the guarana seed improved psychomotor performance and produced positive trends in mood.

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Energy booster

Caffeine, the main constituent of guarana, is believed to be responsible for the increase in energy. However, some researchers think that other compounds present in guarana may also play a role in the energy "boosting" effect, which can lead to increased stimulant effects compared with caffeine alone. Guarana extract is able to induce a stimulant effect in a specific laboratory model using an organism that is insensitive to caffeine. These results have been observed in humans.

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Metabolic

Caffeine, the main constituent of guarana, increases resting energy expenditure and cellular thermogenesis. It also causes an increase in the non-oxidative turnover of fatty acids and in lipid oxidation; however, the net effect on lipid oxidation is small. rnrnThe effects of caffeine on energy expenditure and lipid metabolism appear to be mediated by both sympathetic and non-sympathetic mechanisms. La caféine is often used in combination with l'éphédra for weight loss and appears to have additive pharmacodynamic effects. rnrnA single dose of ephedra in combination with caffeine can increase heart rate from 67 beats per minute to 82 beats per minute in young, healthy individuals. This combination also increases systolic blood pressure and, to a lesser extent, diastolic pressure. Caffeine combined with l'éphédra also increases oxygen consumption. rnrnA clinical study in healthy subjects showed that ingestion of a single dose of 2.72 g of guarana significantly increases the respiratory quotient (an indicator of lipid oxidation) and systolic blood pressure.rnrn

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Cognitive function

Studies in animals have shown that administration of guarana improved cognitive and physical performance. Indeed, a positive effect of guarana on physical capabilities was noted, particularly during periods of stress, and an improvement in memory. In another phase II trial, the effects of different doses of guarana on cognitive abilities in humans were evaluated. The analysis was carried out in a double-blind, placebo-controlled study on 26 subjects over 6 days. Different doses of a standardized guarana extract were investigated. The impact of this treatment on cognition and mood was measured using two scales: the automated assessments of the CDR (Cognitive Drug Research) and the Bond and Lader mood scales. Guarana therefore induced an improvement in memory, mental alertness and satisfaction. The authors suggest that caffeine is not the only active ingredient responsible for the described effects. Other components of this plant could also be involved.

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Hypoglycemic

In vitro research suggests that polyphenols isolated from guarana powder inhibit the enzymes alpha-glucosidase and alpha-amylase, which could contribute to hypoglycemic effects.rnrnIn vivo, it has been shown that an aqueous guarana extract alters the glycemic response after exertion. Thus, 60 minutes after exercise, mice pretreated with the extract maintained their blood glucose while it fell in the control group. After 2 hours, the decrease in blood glucose was smaller in mice pretreated with the guarana extract. rnrnThe mechanism underlying this action would be due to an increase in glycogen breakdown, which would provide the body with a larger source of energy.rnrn

Gastroprotective

One study in rats pretreated with a guarana extract showed that guarana produced a significant reduction in gastric lesions induced by ethanol or indomethacin. Caffeine may not be the only constituent responsible for this protective action. Guarana may also increase gastric acid secretion and delay gastric emptying. This was demonstrated in a clinical study using a plant combination known as YGD, which contains yerba mate (leaves of Ilex paraguayensis), guarana (seeds of Paullinia cupana) and damiana (leaves of Turnera diffusa var. aphrodisiaca).

Satiety-inducing

A double-blind, placebo-controlled clinical study showed the effect of a guarana-based treatment on intestinal transit in 13 healthy subjects. The researchers found that the guarana preparation slowed the progression of food through the stomach by 53% compared with placebo and thus increased the duration of the satiety period.

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Antibacterial

In vitro data have demonstrated the antibacterial and antioxidant effects of ethanol extract from guarana, which are thought to be due to phenolic compounds. Guarana has proven effective against many gastrointestinal pathogens, including Escherichia coli, Salmonella typhimurium and Staphylococcus aureus.rnrnThis provides a theoretical basis for the traditional use of guarana against diarrhea.rnrnMore recently, in vitro research has demonstrated antibacterial activity against Streptococcus mutans, which could have applications in the prevention of dental plaque. Antimicrobial activity was confirmed in vitro by testing guarana seed extracts against foodborne fungi and bacteria.rnrn

Antioxidant

In vitro, it has been shown that guarana powder reduces spontaneous lipid peroxidation.rnrnIn another model, a hydroalcoholic extract of guarana limited fibroblast mortality and the pro-oxidant effects (lipid peroxidation, DNA damage, oxidative stress) induced by a chemical agent. rnrnFinally, a study in healthy elderly subjects showed that individuals who regularly consumed guarana (at least 5 times/week), compared with individuals who did not consume it, had better protection of their LDL against an oxidizing agent (a statistically significant 27% decrease in oxidation of their LDL).rnrn

Hormone metabolism

In human research, acute caffeine ingestion induces an increase in epinephrine and norepinephrine levels, which results in an increased heart rate and provides more energy to the body. There is also evidence that caffeine may be associated with decreased testosterone levels and increased levels of estrone and sex hormone-binding globulin. These findings may explain why some studies have reported associations between caffeine and hormone-dependent conditions such as fibrocystic disease, osteoporosis, breast cancer, and endometriosis.