Stay alert to the perils of too much caffeine

The Irish Times
Health Supplement, p. 13
13 January 2009

DOES IT WORK? GUARANA IS a vine that grows in the rainforests of the Amazon. The name comes from the Guarani tribe who first cultivated the plant to make a drink that gave people energy and brought healing. A 17th century Jesuit missionary reported that the Amazonian tribes valued guarana like Europeans did gold because it gave them enough energy to hunt for days without feeling hungry.

The traditional drink is made from the seeds found within the berries of the vine. These are removed from the fruit, dried and processed into a paste which is then dried. Guarana seeds contain more caffeine than any other plant in the world, and about four times as much caffeine as coffee beans. Traditionally, dried guarana was ground up as needed to make a stimulant drink.

Early in the 20th century, commercial production of guarana drinks began in Brazil. A carbonated beverage was introduced in 1909 and became very popular. More recently, street vendors prepare guarana drinks mixed with fruit and nuts, much like coffee drinks are available here.

Guarana has now emerged onto the global market, especially in sports drinks. These often contain other herbs and claim to provide energy and many other benefits. Commonly, the drinks are said to reduce fatigue, boost sports performance and help people lose weight.

Evidence from studies 

Very little research has been conducted with guarana itself. A few studies have confirmed that guarana keeps people alert, as would be expected given its high caffeine content. However, results have been contradictory regarding people’s performance after taking guarana.

One study found that memory and attention were improved between 2pm and 4pm in sleep-deprived people, but were no different at all other times. Other studies found no benefits in those who were not sleep-deprived.

Many claims about guarana’s beneficial effects are based on studies where people took caffeine. As a weight-loss supplement, caffeine has inconsistent results. It sometimes helps people overcome fatigue to increase physical activity.

Short-term weight loss may occur, but this may result from caffeine’s diuretic effect leading to water loss. One study found that people felt full more quickly after drinking a herbal drink containing guarana.

However, those taking the guarana drink lost only 1lb more than those drinking a placebo. More importantly, guarana has a bitter taste which leads many producers to add large quantities of sugar to these drinks. This may be beneficial for sports performance, but not for those trying to lose weight.

No studies were found using guarana as a sports drink. Studies with caffeine have shown that it releases stored fatty acids which can make more energy available during endurance events. However, large doses of caffeine produced headaches and gastrointestinal disturbances which negatively impacted performances. Since caffeine stimulates frequent urination, it could also lead to dehydration.

Problematic aspects 

As anyone who has had too much tea or coffee knows, there are side effects to large amounts of caffeine. Headaches, tremors and stomach upset can develop into more serious heart palpitations, dizziness and agitation.

People with cardiac arrhythmias, and others seeking to limit caffeine intake, should avoid guarana. The amount of caffeine in guarana products varies considerably and often precise amounts are not stated on labels.


Guarana is commonly found in energy drinks as a natural source of caffeine. Ironically, while the market for such drinks has expanded rapidly around the world, production of guarana in Brazil has barely increased. This has led to questions of how much guarana is being put into these drinks.

Drinks containing guarana provide similar effects as coffee, tea and other caffeinated beverages. Some claim its effects are longer lasting due to other components in guarana, but this has not been evaluated well. As with many things, guarana can be used to excess, leading to physical, psychological and social problems. Beverages high in caffeine may provide a short-term stimulus, but cannot replace getting adequate sleep, exercise or a healthy diet.

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