Behavioral correlates of caffeine consumption by children

Caffeine Consumption through Coffee: Content in the Beverage, Metabolism, Health Benefits and Risks

Caffeine (1,3,7-trimethylxanthine) is the most consumed psychoactive substance in the world, acting by means of antagonism to adenosine receptors, mainly A1 and A2A. Coffee is the main natural source of the alkaloid which is quite soluble and well extracted during the brew’s preparation. After consumption, caffeine is almost completely absorbed and extensively metabolized in the liver by phase I (cytochrome P450) enzymes, mainly CYP1A2, which appears to be polymorphically distributed in human populations. Paraxanthine is the major caffeine metabolite in plasma, while methylated xanthines and methyluric acids are the main metabolites excreted in urine. In addition to stimulating the central nervous system, caffeine exerts positive effects in the body, often in association with other substances, contributing to prevention of several chronic diseases. The potential adverse effects of caffeine have also been extensively studied in animal species and in humans. These aspects will be approached in the present review.

Effects of adolescent caffeine consumption on cocaine self-administration and reinstatement of cocaine seeking

BACKGROUND:

Caffeine consumption by children and adolescents has risen dramatically in recent years, yet the lasting effects of caffeine consumption during adolescence remain poorly understood.

AIM:

These experiments explore the effects of adolescent caffeine consumption on cocaine self-administration and seeking using a rodent model.

METHODS:

Sprague-Dawley rats consumed caffeine for 28 days during the adolescent period. Following the caffeine consumption period, the caffeine solution was replaced with water for the remainder of the experiment. Age-matched control rats received water for the duration of the study. Behavioral testing in a cocaine self-administration procedure occurred during adulthood (postnatal days 62-82) to evaluate how adolescent caffeine exposure influenced the reinforcing properties of cocaine. Cocaine seeking was also tested during extinction training and reinstatement tests following cocaine self-administration.

RESULTS:

Adolescent caffeine consumption increased the acquisition of cocaine self-administration and increased performance on different schedules of reinforcement. Consumption of caffeine in adult rats did not produce similar enhancements in cocaine self-administration. Adolescent caffeine consumption also produced an upward shift in the U-shaped dose response curve on cocaine self-administration maintained on a within-session dose-response procedure. Adolescent caffeine consumption had no effect on cocaine seeking during extinction training or reinstatement of cocaine seeking by cues or cocaine.

CONCLUSIONS:

These findings suggest that caffeine consumption during adolescence may enhance the reinforcing properties of cocaine, leading to enhanced acquisition that may contribute to increased addiction vulnerability.

Mechanisms of the psychostimulant effects of caffeine: implications for substance use disorders

BACKGROUND

The psychostimulant properties of caffeine are reviewed and compared with those of prototypical psychostimulants able to cause substance use disorders (SUD). Caffeine produces psychomotor-activating, reinforcing, and arousing effects, which depend on its ability to disinhibit the brake that endogenous adenosine imposes on the ascending dopamine and arousal systems.

OBJECTIVES

A model that considers the striatal adenosine A2A-dopamine D2 receptor heteromer as a key modulator of dopamine-dependent striatal functions (reward-oriented behavior and learning of stimulus-reward and reward-response associations) is introduced, which should explain most of the psychomotor and reinforcing effects of caffeine.

HIGHLIGHTS

The model can explain the caffeine-induced rotational behavior in rats with unilateral striatal dopamine denervation and the ability of caffeine to reverse the adipsic-aphagic syndrome in dopamine-deficient rodents. The model can also explain the weaker reinforcing effects and low abuse liability of caffeine, compared with prototypical psychostimulants. Finally, the model can explain the actual major societal dangers of caffeine: the ability of caffeine to potentiate the addictive and toxic effects of drugs of abuse, with the particularly alarming associations of caffeine (as adulterant) with cocaine, amphetamine derivatives, synthetic cathinones, and energy drinks with alcohol, and the higher sensitivity of children and adolescents to the psychostimulant effects of caffeine and its potential to increase vulnerability to SUD.

CONCLUSIONS

The striatal A2A-D2 receptor heteromer constitutes an unequivocal main pharmacological target of caffeine and provides the main mechanisms by which caffeine potentiates the acute and long-term effects of prototypical psychostimulants.

Caffeine intake from food and beverage sources and trends among children and adolescents in the United States: review of national quantitative studies from 1999 to 2011

There is increasing concern about potential adverse effects of caffeine in children. Our understanding of caffeine intake relies on studies dating to the late 1990s. This article synthesizes information from national studies since then to describe caffeine consumption, its association with sociodemographic factors, key dietary sources including caffeine-containing energy drinks (CCEDs), and trends in caffeine intake and sources among US children. Findings from the Kanter Worldpanel (KWP) Beverage Consumption Panel and the NHANES showed that caffeine consumption prevalence was generally consistent across studies and over time; more than one-half of 2- to 5-y-olds and ∼75% of older children (>5 y) consumed caffeine. The usual intakes of caffeine were 25 and 50 mg/d for children and adolescents aged 2-11 and 12-17 y, respectively (NHANES 2007-2010). Caffeine consumption correlated with age and was higher in non-Hispanic white children. The key sources of caffeine were soda and tea as well as flavored dairy (for children aged <12 y) and coffee (for those aged ≥12 y). The frequency of CCED use varied (2-30%) depending on study setting, methods, and demographic characteristics. A statistically significant but small decline in caffeine intake was noted in children overall during the 10- to 12-y period examined; intakes remained stable among older children (≥12 y). A significant increasing trend in CCED and coffee consumption and a decline in soda intake were noted (1999-2010). In 2009-2010, 10% of 12- to 19-y-olds and 10-25% of caffeine consumers (aged 12-19 y) had intakes exceeding Canadian maximal guidelines. Continued monitoring can help better understand changes in caffeine consumption patterns of youth.

Caffeine intake in children in the United States and 10-y trends: 2001-2010

BACKGROUND

Because of the increasing concern of the potential adverse effects of caffeine intake in children, recent estimates of caffeine consumption in a representative sample of children are needed.

OBJECTIVES

We provide estimates of caffeine intake in children in absolute amounts (mg) and in relation to body weight (mg/kg) to examine the association of caffeine consumption with sociodemographic factors and describe trends in caffeine intake in children in the United States.

DESIGN

We analyzed caffeine intake in 3280 children aged 2-19 y who participated in a 24-h dietary recall as part of the NHANES, which is a nationally representative survey of the US population with a cross-sectional design, in 2009-2010. Trends over time between 2001 and 2010 were examined in 2-19-y-old children (n = 18,530). Analyses were conducted for all children and repeated for caffeine consumers.

RESULTS

In 2009-2010, 71% of US children consumed caffeine on a given day. Median caffeine intakes for 2-5-, 6-11-, and 12-19-y olds were 1.3, 4.5, and 13.6 mg, respectively, and 4.7, 9.1, and 40.6 mg, respectively, in caffeine consumers. Non-Hispanic black children had lower caffeine intake than that of non-Hispanic white counterparts. Caffeine intake correlated positively with age; this association was independent of body weight. On a given day, 10% of 12-19-y-olds exceeded the suggested maximum caffeine intake of 2.5 mg/kg by Health Canada. A significant linear trend of decline in caffeine intake (in mg or mg/kg) was noted overall for children aged 2-19 y during 2001-2010. Specifically, caffeine intake declined by 3.0 and 4.6 mg in 2-5- and 6-11-y-old caffeine consumers, respectively; no change was noted in 12-19-y-olds.

CONCLUSION

A majority of US children including preschoolers consumed caffeine. Caffeine intake was highest in 12-19-y-olds and remained stable over the 10-y study period in this age group.

Acute and adaptive motor responses to caffeine in adolescent and adult rats

Caffeine is a psychostimulant with intake through foods or beverages tending to increase from childhood through adolescence. The goals of the present study were to examine the effects of caffeine on young adolescent Long-Evans rats and to compare the motor-behavioral responses of adolescent and adult rats to acute and chronic caffeine. Adolescent rats had a biphasic dose-response to caffeine comparable to that reported for adult rats. The magnitude of the motor response to a challenge dose of caffeine (30mg/kg, ip) was similar between adolescent and adult rats. Administration of caffeine in the drinking water (1mg/ml) for a period of 2 weeks led to overall consumption of caffeine which was not significantly different between adolescents and adults when normalized to body mass. There were no impacts of caffeinated drinking water on volume of fluid consumed nor weight gain in either age group compared to age matched controls drinking non-caffeinated tap water. Following this period of caffeine consumption, return to regular drinking water (caffeine withdrawal) led to a significant decrease in baseline movement compared to caffeine-naïve rats. This effect inversion was observed for adolescents but not adults. In addition, the response of the adolescents to the challenge dose of caffeine (30mg/kg, ip) was reduced significantly after chronic caffeine consumption and withdrawal. This apparent tolerance to the caffeine challenge dose was not seen with the adults. Thus, the developing brain of these adolescents may show similar sensitivity to adults in acute caffeine exposure but greater responsiveness to adaptive changes associated with chronic caffeine consumption.

Caffeine use: association with nicotine use, aggression, and other psychopathology in psychiatric and pediatric outpatient adolescents

The objective of this study was to evaluate the relationship between caffeine use, other drug use, and psychopathology in adolescents, using self-report measures. The study group consisted of 132 adolescents (average age 14.01 ± 2.06 years, 52% female, 19% African American, 5% other categories, 76% Caucasian). Most (47%) were recruited from a child psychiatry clinic with emphasis on youth with disruptive disorders, with 35% from an adolescent pediatric clinic with emphasis on prevention of risk-taking behavior and 18% from a pediatric clinic for families with limited resources. Subjects were consecutively recruited before or after regular clinic visits. Consent was obtained from parents and assent from the youth. High caffeine consumption was associated with daily cigarette use; aggressive behavior; conduct, attention deficit/hyperactivity, and social problems; and increased somatic complaints in adolescents.

Psychostimulant and other effects of caffeine in 9- to 11-year-old children

BACKGROUND

Recent research on adults suggests that "beneficial" psychostimulant effects of caffeine are found only in the context of caffeine deprivation; that is, caffeine improves psychomotor and cognitive performance in habitual caffeine consumers following caffeine withdrawal. Furthermore, no net benefit is gained because performance is merely restored to "baseline" levels. The effects of caffeine in children is an under-researched area, with only a handful of studies being carried out in the US where children's consumption of caffeine appears to be lower on average than in the UK.

METHOD

Twenty-six children aged between 9 and 11 years completed a double-blind, placebo-controlled study. Habitual caffeine consumers (mean daily caffeine intake = 109 mg) and non/low-consumers (12 mg) were tested on two separate days following overnight caffeine abstinence. On each day measures of cognitive performance (a number search task), and self-rated mood and physical symptoms, including alertness and headache, were taken before and after administration of 50 mg of caffeine, or placebo.

RESULTS

At baseline (before treatment), the habitual consumers showed poorer performance on the cognitive test than did the non/low-consumers, although no significant differences in mood or physical symptoms were found between the two groups. There were significant habit by treatment (caffeine vs. placebo) interactions for accuracy of performance and headache, and a significant main effect of treatment for alertness. Post hoc comparisons showed that caffeine administration improved the consumers' accuracy on the cognitive test (to near the level displayed by the non/low-consumers at baseline), but that it had no significant effect on the non/low-consumers' performance. In the consumers, caffeine prevented an increase in headache that occurred after placebo, and it increased alertness relative to placebo. Again, however, caffeine did not significantly affect levels of headache or alertness in the non/low-consumers.

CONCLUSIONS

These results suggest that, like adults, children probably derive little or no benefit from habitual caffeine intake, although negative symptoms associated with overnight caffeine withdrawal are avoided or rapidly reversed by subsequent caffeine consumption.

Beverage caffeine intake in US consumers and subpopulations of interest: estimates from the Share of Intake Panel survey

Concerns exist about the potential adverse health effects of high consumption of dietary caffeine, especially in children and pregnant women. Recommended caffeine intakes corresponding to no adverse health effects have been suggested recently for healthy adults (400-450 mg/day), for women contemplating pregnancy (300 mg/day), and for young children age 4-6 years (45 mg/day). To determine whether current caffeine intake approaches these levels, intake from major dietary sources (coffee, tea and carbonated soft drinks) were measured in 10,712 caffeinated beverage consumers in the 1999 US Share of Intake Panel, a targeted beverage survey. Mean caffeine intakes in adult caffeinated beverage consumers ranged from 106 to 170 mg/day (90th percentile intake was 227-382 mg/day). In children 1-5 and 6-9 years, mean caffeine intakes were 14 and 22 mg/day, respectively; corresponding 90th percentile intakes were 37 and 45 mg/day. Pregnant women consumed an average of 58 mg/day (157 mg/day at the 90th percentile), and women of reproductive age ingested 91-109 mg/day (229-247 mg/day at the 90th percentile). These data show that while mean caffeine intakes are within recommended safe levels, heavy consumers of certain subpopulations, including young children and women contemplating pregnancy, might benefit from dietary advice.

Effects of caffeine on human health

Caffeine is probably the most frequently ingested pharmacologically active substance in the world. It is found in common beverages (coffee, tea, soft drinks), in products containing cocoa or chocolate, and in medications. Because of its wide consumption at different levels by most segments of the population, the public and the scientific community have expressed interest in the potential for caffeine to produce adverse effects on human health. The possibility that caffeine ingestion adversely affects human health was investigated based on reviews of (primarily) published human studies obtained through a comprehensive literature search. Based on the data reviewed, it is concluded that for the healthy adult population, moderate daily caffeine intake at a dose level up to 400 mg day(-1) (equivalent to 6 mg kg(-1) body weight day(-1) in a 65-kg person) is not associated with adverse effects such as general toxicity, cardiovascular effects, effects on bone status and calcium balance (with consumption of adequate calcium), changes in adult behaviour, increased incidence of cancer and effects on male fertility. The data also show that reproductive-aged women and children are 'at risk' subgroups who may require specific advice on moderating their caffeine intake. Based on available evidence, it is suggested that reproductive-aged women should consume </=300 mg caffeine per day (equivalent to 4.6 mg kg(-1) bw day(-1) for a 65-kg person) while children should consume </=2.5 mg kg(-1) bw day(-1).

Effects of caffeine on development and behavior in infancy and childhood: a review of the published literature

The Medline literature on the behavioral effects of caffeine in infants and children are reviewed. There has been little recent work in this area. Generally, caffeine is well tolerated in usual dietary amounts, and there is evidence that individuals differ in their susceptibility to caffeine-related adverse effects, which in turn may influence their consumption. Overall, the effects of caffeine in children seem to be modest and typically innocuous.