New caffeine consumption patterns
Coffee and tea are the main food sources containing caffeine, and 80% of the caffeine in the average diet comes from coffee. Although caffeine has been consumed throughout history and throughout the world, today it is also used to fortify various foods and beverages, including the popular "so-called energy drinks". In its opinion on the assessment of risks of the consumption of so-called energy drinks, which contain large amounts of caffeine, ANSES showed that these new consumption patterns impact consumers who until recently were rarely exposed to caffeine, especially children and adolescents, at often high levels, and sometimes in conjunction with a sporting activity or combined with alcohol.
ANSES has drawn special attention to the role of caffeine in the onset of the adverse effects that have been reported to the Agency (in particular cardiovascular, psycho-behavioural, neurological, etc.) in a nutrivigilance context. These results have prompted ANSES to issue recommendations on caffeine consumption, especially in "susceptible" population groups (children, adolescents, pregnant and breastfeeding women and individuals who are intolerant to the effects of caffeine).
Caffeine: description and mode of action
Caffeine is naturally present in over 60 different plants, including coffee, kola nut, guarana and yerba mate, and can also be produced through chemical synthesis. Once ingested, caffeine spreads rapidly throughout the body. It can cross the blood-brain and placental barriers, and can also pass into breast milk. Its main effect is to counter sleepiness thanks to the activation of certain receptors in the brain.
However, individuals show significantly different responses to caffeine, both with regard to its ability to delay sleep and the quality of sleep itself, and to its expected effects on physical performance. This variability is due to a person’s genotype, physiological state, individual caffeine consumption habits and to factors such as co-exposure with cigarette smoking or certain medications. Such inter-individual variability makes it difficult to establish specific daily doses not to be exceeded if one is to maintain good health. Moreover, in individuals suffering from certain pathologies (i.e. liver disease), the metabolism of caffeine is slowed down and its adverse effects (hypertension, mental disorders, urinary and faecal incontinence, ulcers, gastro-oesophageal reflux disease) can be amplified. This variability in the biological effects of caffeine makes the risk analysis of certain consumption levels difficult. And since the interactions between these different variability factors can be complex, it is difficult to isolate the effects of each factor.
Specific health effects in children and adolescents
Harmful effects on sleep
Caffeine is used specifically for staying awake and alert, and the negative effects of caffeine on sleep are also well known. They include delayed sleep, shorter sleep periods and poor-quality sleep. However, caffeine’s effects on sleep are highly variable and depend on the age, sex and consumption habits of individuals.
Sleep characteristics (duration of sleep, waking and sleeping hours) evolve with age, and major changes occur at puberty. Adolescents therefore have a natural tendency to fall asleep late, which can be exacerbated by the consumption of stimulants such as caffeine. Since school obligations require them to wake up early, a lack of sleep is frequently the result. However, the consequences of a sleep deficiency are numerous. It can cause daytime drowsiness (which may lead to a vicious cycle of caffeine consumption to fight this drowsiness), can affect cognitive abilities and learning performance, and engender a number of behavioural problems. Sleep disorders are also linked to an increased risk of diseases such as high blood pressure, cardiovascular disease, diabetes, obesity, anxiety and depression, although the nature of this relationship has not yet been elucidated.
In children and adolescents, agitation and excitement, nervousness, tachycardia and thoracic pains are symptoms that can be observed following ingestion of large amounts of caffeine. It is therefore troubling to observe that large amounts of so-called energy drinks (3-4 cans) are being consumed by young children.
Developmental risks and addictive behaviour
Although the risk of developing a dependency on caffeine remains controversial, certain studies show that according to generally accepted criteria approximately 20% of adolescents who consume caffeine could be considered as caffeine-dependent. Early consumption of caffeine might also promote the onset of addictive behaviours (as is the case with other substances such as alcohol, tobacco and marijuana). This could be explained by the immature neocortex (the part of the brain involved in perception and reaction) of children and young adolescents, and a negative effect on control over a part of the brain involved in emotions and in the sleep-wake cycle.
Poor-quality sleep could also increase the risk of addictive behaviour, especially in children and adolescents, whose brains are still immature.
Avoid mixing alcohol or physical exercise with caffeine
Caffeine raises blood pressure and can cause tachycardia, one of the typical symptoms of caffeine intoxication. The intensity of this effect seems to increase when high doses of caffeine are ingested and when the subject is not used to caffeine consumption. Additionally, in predisposed individuals alcohol tends to worsen the heart rhythm disorders that can caffeine can cause. It is therefore recommended to avoid mixing alcohol and caffeine, especially since this can promote several other risks, including masking the depressive effects of alcohol, alcohol dependence, dehydration, and impaired kidney function.
Furthermore, certain people consume caffeine-rich energy drinks in order to improve their physical performance. While these beverages seem to have no effect on performance during short periods of very intense exercise, the caffeine in them may improve performance in certain individuals during endurance-type activities. However, during physical exercise, caffeine consumption is a cardiac risk factor in people with a predisposition for heart problems and brings about an increase in body temperature, which in turn increases the risk of heat stroke. For these reasons, caffeine should not be consumed during physical activity. So-called energy drinks should not be used as a substitute for sports drinks, which are beverages specifically formulated to fulfil a certain number of nutritional requirements during physical exercise.
ANSES's recommendations and research to be conducted
Based on the results of its study, ANSES recommends that all consumers use moderation when drinking caffeine-based beverages. Based on the various internationally-based thresholds, a significant proportion of the French population was found to exceed recommended caffeine levels:
- approximately 30% of the adult population and 1 to 2% of children and adolescents exceed the limit set for anxiety;
- 11% of 3- to 10-year-olds and 7% of 11- to 14-year-olds exceed the limit for the development of a tolerance to caffeine and the onset of withdrawal symptoms;
- close to 7% of the adult population exceed the limit above which more general chronic toxicity is suspected (effects on bone and heart health, cancer, male fertility, etc.).
The Agency recommends that consumers:
- be particularly vigilant concerning caffeine intake, especially:
- pregnant and breastfeeding women (caffeine can increase the risk of impaired foetal growth and can pass into breast milk);
- children and adolescents, who are especially susceptible to caffeine, and who may suffer from sleep disturbances, daytime drowsiness and a risk of developing addictive behaviour later in life;
- people susceptible to the effects of caffeine or who suffer from certain pathologies, especially certain cardiovascular, psychiatric or neurological disorders, kidney failure, or severe liver disease.
- avoid consuming caffeine along with alcohol;
- avoid consuming caffeine along with physical exercise
ANSES considers that it is necessary to conduct further research, since interindividual variability in the effects of caffeine need to be better accounted for in studies, and the dose-effect relationship for caffeine as well as possible interactions with other substances (such as the taurine found in certain so-called energy drinks) need to be better documented.
In a study of American school children aged 12-18, 33% of those studied declared that they often fell asleep during class, and caffeine consumption was 76% higher in this group. Children (aged 6-10) who drank caffeine-based beverages also got an average of 15 minutes less sleep each night than those who did not. In addition, a comparison of adolescents (aged 14-18) who were "night birds" and those who were "early birds" showed that those who tended to stay up late slept less, complained more frequently of daytime drowsiness and suffered from higher rates of attention disorders. They also consumed more caffeine-based beverages in addition to substances for inducing sleep.