I have heard that guarana doesn't have caffeine, but something else that stimulates you. Is it just the sugar in guarana drinks? How does it work?
R. T., Costa Rica
Guarana, the plant, contains caffeine, and this is identical to the caffeine in coffee, tea, and cola. I love to talk about caffeine, because it is one my own favorite plant derived molecules, and it isn't as bad as people think. Societal opinion about caffeine is a classic case of people making a snap judgements prior to more thorough scientific investigation.
People also have historically assumed that sugar revs you up, perhaps because we intuit it can be used for energy--but we don't necessarily use it for energy. Sugar can also be stored (as either glycogen or fat). Once again, science is showing we can't trust our first opinions: sugar, or carbohydrates in general may even have sedating effects for some.
Here are some excerpts from my book on how guarana works:
Paullinia cupana, Paullinia sorbilis
History and Folklore If you are from South America, you already know all about this herb. I was introduced to guarana ages ago, through a spell-checker.
Fumbling about as a novice on one of the very first word-processing software programs available, I was writing a letter to my Norwegian sister in law, Jurene. Pressing the wrong button, I was startled to see her name changed to Guarana in every instance. “Dear Guarana,” the letter now began. “What on earth is that?” I wondered, irked that the demonstrably dim spell-checker knew more words than I did. I had to look it up. I learned my spell-checker believed my relation was “an invigorating South American shrub”.
I have been further educated by my Brazilian students that guarana is the national drink of Brazil, and, eyes gleaming, they proclaim absolute devotion to it. As an unabashed coffee lover I can relate—its main therapeutic constituent is caffeine.
Guarana is both a climbing, Amazonian evergreen vine, and the drink made from its seeds. Indian legend holds the plant grew from the eyes of a divine child that was killed by a serpent. Guarani Indians were the first to process the seeds, hence its name. After the seeds are shelled and roasted, they are powdered and mixed with water to form a dough. This is molded into hard cakes or bars. Amazonian Indians used these on-the-go guarana bars by grating off a piece for themselves with a hard fish bone when they needed a little extra zip. This form of guarana is likened to bitter chocolate, only astringent and dry, without the fat found in cocoa butter.
Besides abating fatigue, guarana is considered an aphrodisiac. Traditionally it is used to treat mild digestive upset—its tannins may help in that arena—and headache—an action probably assisted by its caffeine.
Guarana seeds are also mixed with cassava and allowed to ferment to make one of Brazil’s favorite drinks. Sugary, amber-colored guarana sodas, however, are huge in South America, and most of its devotees say it’s not just the caffeine but guarana’s contribution of an unusual, spicy, berry-like flavor not found in other sodas. These have made their inroads into U.S. grocery shelves, marketed under the term “energy drinks”, and sporting confidence-inspiring names, like “Bawls”.
What’s in it Guarana contains the stimulant purine alkaloids caffeine (2-7.5%) and smaller amounts of theophylline and theobromine. Its tannins are proanthocyanidins (12%), and also contains cyanolipids such as 2,4-dihydroxy-3-butyronitrile. It also contains trace amounts of the saponin fish poison timbonine.
How Scientists Think it Works
Guarana’s main active ingredient is caffeine. Like tea, coffee, cocoa, and mate’, these unrelated plants all possess differing amounts of stimulant molecules called methylxanthines: the classic stimulant trio of caffeine, theophylline, and theobromine. They all tend to work the same way, with different potencies and subspecialities. Caffeine is the most prominent one in guarana, and guarana has more caffeine than coffee. People taking guarana typically experience the same effects as those drinking coffee.
You may already be familiar with caffeine’s most obvious effects, like stimulation, faster heartbeat, and an exceptional urge to urinate. Caffeine also stimulates your gut’s release of digestive enzymes and acid, discourages blood clots, and briefly raises your blood pressure, as if you have been climbing a flight of stairs. Regular caffeine consumers, however, do not have high blood pressure.
A lot of caffeine’s other effects are signature moves of the “fight or flight” nervous system. This readies you for action, and some of these effects can be exploited therapeutically. For example, blood vessels in muscles are widened, allowing them greater access to blood sugar. At the same time, blood sugar is released from stores in the liver, and fat breakdown is stimulated (hooray!), the products of which can also be used to feed cells poised for action. Caffeine tends to suppress appetite—eating is not something you need to do while fighting or fleeing—plus its stimulating effects form the rationale for its addition to diet aids. Blood vessels in other areas are constricted, like in the brain and skin, conserving its delivery to muscles and lungs. The constriction of blood vessels in your brain by caffeine makes it useful in treating vascular headaches, and you may notice its addition to some over the counter analgesics and prescription migraine medicines. Caffeine opens up the respiratory system, allowing you to get more oxygen. Theophylline, one of the other methylxanthines, is better at this than caffeine, however, and is therefore used in asthma medications.
How does the caffeine in guarana and other plants perform these tricks? Caffeine is an adenosine receptor antagonist. The main effects of caffeine are attributed to its antagonism of a molecule called adenosine. Caffeine does other things, too, like increasing calcium in muscle cells, making them twitchy by lowering the threshold stimulus needed for them to contract. Caffeine may also stimulate histamine receptors in your gut, too, increasing digestive juices. But the main effects of caffeine are through its inhibition of a sleep-inducing molecule called adenosine.
Adenosine is released as part of a larger molecule called adenosine triphosphate, or ATP, from stimulatory nerves, but it doesn’t stimulate. It is released at the same time as the stimulatory fight-or-flight neurotransmitter, norepinephrine, perhaps as a means to keep norepinephrine from getting out of hand. The slow, spontaneous breakdown of ATP lingering outside the nerve releases adenosine. This adenosine doubles back on its tracks, and binds to adenosine receptors on the nerve that released it.
Adenosine blunts the nerves’ ability to release the stimulatory norepinephrine, so adenosine inhibits brain activity, and it makes you sleepy. Adenosine also accumulates throughout the day as ATP is broken down during its use to fuel reactions that just would not go on their own; reactions that require energy.
So, as you spend energy throughout the day, adenosine builds up, and it’s binding to adenosine receptors in your brain shuts down your brains’ activity.
Caffeine and other methylxanthines look a lot like adenosine, and also temporarily stick to adenosine receptors, blocking adenosine’s access to them. This keeps you from getting sleepy. Besides allowing the fight-or-flight stimulant norepinephrine to work unopposed by adenosine, caffeine has indirect effects that boost dopamine and serotonin, and this could explain why we get a pleasure-enhancing mood reward from consuming it.
Scientists speculate that caffeine’s effect on these hormones may explain why large studies have shown that habitual caffeine consumers are less likely to get Parkinson’s disease or to commit suicide. Despite our puritanical impulses to portray anything that makes us feel so good as a danger, caffeine has several health benefits, although certain people should not have it. For a summary of all of caffeine’s positive and negative disease risks, see “interesting facts”, below.
Guarana also contains a lot of tannin. The effects of guarana tannin are less well known. Small doses of tannin are benign and can even be helpful. Tannin cross-link proteins, pulling them tight, and this skin-tightening effect is meant by “astringent”. Tannins “tan” the lining of your mouth and digestive tract in a mild way. This forms a temporary, protective barrier against gastrointestinal irritants, hence guarana’s traditional use in treating indigestion. Large doses, however, can upset your stomach.
Unlike mate', guarana is not (so far at least) linked to increased cancer risk. Another tannin-containing South American herb, yerba mate’ (see also), is very popular and part of South American cultural traditions, just as wine drinking is among European ones. Like guarana, it has both caffeine and a high tannin content. Mate’, however, has been repeatedly linked to an increased risk of certain cancers, and we aren’t sure why. It certainly isn’t its caffeine content. Early studies suggesting caffeine was a carcinogen were confounded by coffee drinkers’ tendency to smoke.
Caffeine has been vindicated of these charges in numerous, better-designed studies, and the American Cancer Society officially states that caffeine does not cause cancer. Tannin, on the other hand, theoretically could, if you have loads of it, and some have proposed this is behind mate’s’ increased cancer risk.
There have been no associations of guarana with cancer, but no one has performed epidemiological cancer-risk studies on it, either. If you want to limit any tannin’s actions, have it with protein. The tannin reacts with the protein and not with you.
Good Uses…And Not So Good
Guarana gives you an energy boost, and can stop a vascular headache, but don’t overdo it. Too much stimulation will make you jittery and bad-tempered, and any fine motor controls you require go down the drain. I’ll never forget being impressed by the latter effect, staying up late doing lab work, drinking coffee, and discovering that my hands under my microscope magnified their tiny caffeine-induced tremors into awesome, large scale oscillations. It dawned on me as the explanation for my clumsy work, and I sadly pitched my coffee in order to continue my microscopy. If you do fine artwork or anything requiring careful control of your hands, don’t have guarana beforehand.
Watch out for withdrawal. Like other caffeine containing beverages, guarana is pleasure-enhancing and addictive; though this is not as sinister as it sounds. The tolerance you develop to caffeine is mild, and unlike many other additive drugs, caffeine pharmacology works differently. It isn’t something that you need more and more of to continue having the same effect. You won’t end up selling your house and car to fund your caffeine habit, for example.
There are health benefits to moderate regular caffeine drinking, too though not everyone should have it. It you are used to guarana or other caffeinated substances, their sudden withdrawal may cause blood to flood into your brain, causing headache, and the increased number of adenosine receptors that you make while taking caffeine makes you more susceptible to adenosine’s sleep-inducing effects, making you groggy.
Certain people should limit their guarana. It is not for the insomniac. Caffeine is a common culprit in causing insomnia, and guarana’s caffeine content is higher than coffee’s. Caffeine can cause some people to have an irregular heartbeat, and if you think you are one of these people, don’t have guarana. Certainly, if you don’t like how it makes you feel, don’t take it! If you are not a regular consumer of caffeine, it may boost your blood pressure, though those who take it regularly don’t experience this effect. Because caffeine can enter fetal circulation, pregnant women are advised to have no more than one cup of coffee per day, and since guarana has more caffeine, guarana abstinence seems wise. Unless you want a fussy, sleepless baby, don’t nurse while taking guarana, either. The caffeine in it is transported through breast milk.
Guarana is not for pets. Although the problem is more often seen with chocolate, pets should not be exposed to methylxanthines in general, because they resond differently than humans and in some cases it can kill them.
Various forms of guarana have precautions, too. The diet and cognitive aids containing guarana typically contain many other herbs with unknown safety records, and since it’s not clear they work, avoid them. And although there are some “diet” versions, most guarana sodas and “energy drinks” are brimming with sugar. Since energy is measured in calories, why not rename them “calorie drinks”? Their sugar can certainly make you gain weight. Sugary sodas cause tooth decay, too.
The tannins in guarana are an unknown, but a concern. It is not known if their presence in the herb mate’ causes cancer, for example. Tannins do limit your absorption of protein, because they bind to proteins in your gut. To limit the action of tannins in your gut, some have suggested taking high-tannin containing herbs like guarana with milk, to keep them preoccupied enough with milk proteins.
Interesting facts: Through caffeine, nature teaches us once again that no molecule is entirely bad or entirely good. Regular caffeine consumption has been associated with a decreased risk of committing suicide, and less risk of developing Parkinson’s disease, gallstones, liver disease, and type 2 diabetes. On the other hand, it can increase urinary loss of calcium, although studies attempting to link it to osteoporosis have been inconclusive, perhaps because dietary calcium compensated for the loss in the people studied. It was once believed caffeine stimulated breast cyst formation, but this is no longer held to be true; well-designed studies have found no evidence to support this. Caffeine can cause some people to have an irregular heart beat, although it is not associated with causing heart disease. It can enter fetal circulation and its effects on fetuses are unknown, but not associated with birth defects. However, a Danish study found that women consuming more than 300 mg of caffeine a day were more likely to risk a stillborn child, so pregnant women should limit it or avoid it entirely.
Evidence of Action There are not many studies of the effects of guarana on humans. Its effects on cognitive performance are contradictory. One double blind study says it had no significant effect on elderly volunteers compared to caffeine or placebo(1), while another double blind placebo controlled study suggested guarana gave participants moderately better attention on mental tests, but slightly worse accuracy in their answers(2).
Two studies examine guarana as a weight loss agent, but unfortunately, mixed with other herbs, so it is hard to say which herb is doing what. Healthy volunteers consuming guarana mixed with yerba mate’ and damiana, showed significantly delayed gastric emptying compared to placebo, theoretically helping them retain a feeling of fullness(3). Mice fed solely guarana, or caffeine, however, showed no change gastrointestinal transit, in another study(4). After 45 days of taking this mixture, significant weight loss of around 11 pounds (5 kg) was seen, and for those who continued on the extract for a year, the weight was not regained.
Another mixture containing guarana and the now widely banned ephedra showed significantly greater loss of weight and fat than those taking placeboes(5), but it should be noted that 11 of the 35 subjects in the active group withdrew before the study was complete, complaining of chest pain, heart palpitations, increased blood pressure, and irritability, and it is likely that a lot of these side effects were caused by ephedra, which was banned for its toxic and sometimes fatal effects on the heart.
Guarana contributes caffeine, which is an appetite suppressant and stimulant, and this theoretically could have contributed to the effects in these studies. However, there is no way to tell whether guarana caused the weight loss in these studies of herbal mixtures.
Caffeine also stimulates an increase in blood sugar, blood pressure, and heart rate, all of which were significantly elevated in the later studies’ herb-taking volunteers as well. Mice fed guarana also experienced a significant surge in blood sugar after an hour, from its storage form, glycogen, in the liver(6). This significantly prevented them from experiencing a drop in blood sugar during exercise. Rats fed guarana had better endurance in swimming tests, and showed no ill effects from the herb(7).
Animal studies hint that guarana isn’t harmful, and it could provide certain health benefits. A study with rabbits fed guarana showed their platelets were less likely to clot(8), a known effect of caffeine. Guarana also prevented chemical induced liver cancer in mice(9), and protected rats from indomethacin or alcohol caused stomach injury(10). No toxic or adverse effects of guarana on behavior or organ tissues of rats or mice were seen even at high doses(11). Additionally, an antioxidant effect was observed in the form of decreased membrane oxidation (lipid peroxidation.)
The Bottom Line
· Guarana exhibits therapeutic actions through its high caffeine content. Caffeine works primarily by blocking a sleep-inducing molecule called adenosine.
· Because of its caffeine, guarana is a stimulant, and can be effectively used to treat vascular headaches. It is not clear whether it boosts mental ability or works as a diet aid, however.
· Guarana also has tannins, which in small doses can relieve indigestion, but in large doses can cause it. The high dose of tannins from another stimulant South American herb mate’ might increase cancer risk, but no one knows whether guarana is associated with cancer, as well.
· Although regular, moderate caffeine intake is associated with health benefits, it should not be taken in excess, it can cause withdrawal, and certain people should not have it. People prone to irregular heartbeat and pregnant or nursing women should avoid guarana.
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7 Espinola EB, Dias RF, Mattei R, Carlini EA. Pharmacological activity of Guarana (Paullinia cupana Mart.) in laboratory animals. J Ethnopharmacol. 1997 Feb;55(3):223-9.
8 Bydlowski SP, Yunker RL, Subbiah MT. A novel property of an aqueous guarana extract (Paullinia cupana): inhibition of platelet aggregation in vitro and in vivo. Braz J Med Biol Res. 1988;21(3):535-8.
9 Fukumasu H, Silva TC, Avanzo JL, Lima CE, Mackowiak II, Atroch A, Spinosa HD, Moreno FS, Dagli ML. Chemopreventive effects of Paullinia cupana Mart var. sorbilis, the guarana, on mouse hepatocarcinogenesis. Cancer Lett. 2005 May 7
10 Campos AR., et. al,. op. cit.
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