Guarana: benefits, dosage, contraindications

Neurological

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

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Bioenergizing

Caffeine, the main constituent of guarana, is considered responsible for the energy increase. However, some researchers think other compounds present in guarana may also play a role in the "energy-boosting" effect, potentially leading to heightened stimulant effects compared to caffeine alone. Guarana extract can induce a stimulant effect in a specific laboratory model using a caffeine-resistant organism. These results have been seen in humans as well.

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Metabolic

Caffeine, the main constituent of guarana, increases resting energy expenditure and cellular thermogenesis. It also leads to an increase in non-oxidative fatty acid turnover and lipid oxidation; however, the net effect on lipid oxidation is minor. The effects of caffeine on energy expenditure and lipid metabolism seem to be mediated by sympathetic and non-sympathetic mechanisms. Caffeine is often used in combination with ephedra for weight loss and seems to have additive pharmacodynamic effects. A 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 degree, diastolic pressure. Caffeine combined with ephedra also increases oxygen consumption. A clinical study in healthy subjects showed that ingesting a single dose of 2.72g of guarana significantly increases the respiratory quotient (a reflection of lipid oxidation) and systolic blood pressure.

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Cognitive function

Studies in animals have shown that administration of guarana improves cognitive and physical performance. Indeed, a positive action of guarana on physical abilities, particularly during periods of stress, and an improvement in memory capacities has been noted. In another phase II trial, the effects of different doses of guarana on cognitive abilities in humans were evaluated. The analysis was conducted as a double-blind, placebo-controlled test on 26 subjects over 6 days. Different doses of a standardized guarana extract were studied. The impact of this treatment on cognition and mood was measured using two scales: CDR's (Cognitive Drug Research) automated assessments and Bond and Lader mood scales. Guarana thus led to improvements in memory, alertness, and satisfaction. The authors suggest that caffeine is not the only active component responsible for the described effects. Other components of this plant may 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. In vivo, it has been shown that an aqueous extract of guarana affects the glycemic response after exercise. Thus, 60 minutes post-exercise, mice pretreated with the extract maintained their blood sugar levels while these dropped in the control group. After 2 hours, the drop in blood sugar was less in mice pretreated with the guarana extract. The mechanism behind this action is thought to be due to an increase in glycogen breakdown, allowing the body to have a more substantial energy source.

Gastroprotective

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

Satiating

A double-blind, placebo-controlled clinical study showed the influence of a guarana-based treatment on the intestinal transit of 13 healthy subjects. Researchers found that the guarana-based preparation slowed food progression in the stomach by 53% compared to placebo, thereby increasing the duration of the satiety period.

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Antibacterial

In vitro data demonstrated the antibacterial and antioxidant effects of the ethanolic extract of guarana, believed to be due to phenolic compounds. Guarana was found to be effective against numerous digestive pathogens, including Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus. This provides a theoretical basis for the traditional use of guarana against diarrhea. More recently, in vitro research demonstrated antibacterial activity against Streptococcus mutans, which could have applications in preventing dental plaque formation. The antimicrobial activity was confirmed in vitro by testing guarana seed extracts against fungi and food-borne bacteria.

Antioxidant

In vitro, it has been shown that guarana powder reduces spontaneous lipid peroxidation. In another model, a hydro-alcoholic extract of guarana limited fibroblast mortality and pro-oxidant effects (lipid peroxidation, DNA damage, oxidative stress) induced by a chemical agent. Finally, a study in healthy elderly subjects showed that individuals who regularly consumed guarana (at least 5 times/week) had better protection of their LDL against an oxidizing agent (27% statistically significant reduction in LDL oxidation) compared to non-consumers.

Hormonal metabolism

In human research, acute caffeine ingestion induces an increase in epinephrine and norepinephrine levels, leading to increased heart rate and providing 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 results could explain why some studies have reported associations between caffeine and hormone-dependent conditions such as fibrocystic disease, osteoporosis, breast cancer, and endometriosis.