Absorption of caffeine from tea, coffee, and coca cola

Current therapeutic targets and multifaceted physiological impacts of caffeine

Caffeine, which shares consubstantial structural similarity with purine adenosine, has been demonstrated as a nonselective adenosine receptor antagonist for eliciting most of the biological functions at physiologically relevant dosages. Accumulating evidence supports caffeine's beneficial effects against different disorders, such as total cardiovascular diseases and type 2 diabetes. Conversely, paradoxical effects are also linked to caffeine ingestion in humans including hypertension-hypotension and tachycardia-bradycardia. These observations suggest the association of caffeine action with its ingested concentration and/or concurrent interaction with preferential molecular targets to direct explicit events in the human body. Thus, a coherent analysis of the functional targets of caffeine, relevant to normal physiology, and disease pathophysiology, is required to understand the pharmacology of caffeine. This review provides a broad overview of the experimentally validated targets of caffeine, particularly those of therapeutic interest, and the impacts of caffeine on organ-specific physiology and pathophysiology. Overall, the available empirical and epidemiological evidence supports the dose-dependent functional activities of caffeine and advocates for further studies to get insights into the caffeine-induced changes under specific conditions, such as asthma, DNA repair, and cancer, in view of its therapeutic applications.

Potential Benefits of Coffee Consumption on Improving Biomarkers of Oxidative Stress and Inflammation in Healthy Individuals and Those at Increased Risk of Cardiovascular Disease

Cardiovascular diseases (CVDs) are considered the predominant cause of death globally. An abnormal increase in biomarkers of oxidative stress and inflammation are consistently linked with the development and even progression of metabolic diseases, including enhanced CVD risk. Coffee is considered one of the most consumed beverages in the world, while reviewed evidence regarding its capacity to modulate biomarkers of oxidative stress and inflammation remains limited. The current study made use of prominent electronic databases, including PubMed, Google Scholar, and Scopus to retrieve information from randomized controlled trials reporting on any association between coffee consumption and modulation of biomarkers of oxidative stress and inflammation in healthy individuals or those at increased risk of developing CVD. In fact, summarized evidence indicates that coffee consumption, mainly due to its abundant antioxidant properties, can reduce biomarkers of oxidative stress and inflammation, which can be essential in alleviating the CVD risk in healthy individuals. However, more evidence suggests that regular/prolonged use or long term (>4 weeks) consumption of coffee appeared to be more beneficial in comparison with short-term intake (<4 weeks). These positive effects are also observed in individuals already presenting with increased CVD risk, although such evidence is very limited. The current analysis of data highlights the importance of understanding how coffee consumption can be beneficial in strengthening intracellular antioxidants to alleviate pathological features of oxidative stress and inflammation to reduce CVD risk within the general population. Also covered within the review is essential information on the metabolism and bioavailability profile of coffee, especially caffeine as one of its major bioactive compounds.

The human lens: An antioxidant-dependent tissue revealed by the role of caffeine

Cataract is the leading cause of blindness worldwide and surgery is the only option to treat the disease. Although the surgery is considered to be relatively safe, complications may occur in a subset of patients and access to ophthalmic care may be limited. Due to a growing and ageing population, an increase in cataract prevalence is expected and its management will become a socioeconomic challenge. Hence, there is a need for an alternative to cataract surgery. It is well known that oxidative stress is one of the main pathological processes leading to the generation of the disease. Antioxidant supplementation may, therefore, be a strategy to delay or to prevent the progression of cataract. Caffeine is a widely consumed high-potency antioxidant and may be of interest for the prevention of the disease. This review aims to give an overview of the anatomy and function of the lens, its antioxidant and reactive oxygen species (ROS) composition, and the role of oxidative stress in cataractogenesis. Also, the pharmacokinetics and -dynamics of caffeine will be described and the literature will be reviewed to give an overview of its anti-cataract potential and its possible role in the prevention of the disease.

Pharmacokinetics of Caffeine: A Systematic Analysis of Reported Data for Application in Metabolic Phenotyping and Liver Function Testing

Caffeine is by far the most ubiquitous psychostimulant worldwide found in tea, coffee, cocoa, energy drinks, and many other beverages and food. Caffeine is almost exclusively metabolized in the liver by the cytochrome P-450 enzyme system to the main product paraxanthine and the additional products theobromine and theophylline. Besides its stimulating properties, two important applications of caffeine are metabolic phenotyping of cytochrome P450 1A2 (CYP1A2) and liver function testing. An open challenge in this context is to identify underlying causes of the large inter-individual variability in caffeine pharmacokinetics. Data is urgently needed to understand and quantify confounding factors such as lifestyle (e.g., smoking), the effects of drug-caffeine interactions (e.g., medication metabolized via CYP1A2), and the effect of disease. Here we report the first integrative and systematic analysis of data on caffeine pharmacokinetics from 141 publications and provide a comprehensive high-quality data set on the pharmacokinetics of caffeine, caffeine metabolites, and their metabolic ratios in human adults. The data set is enriched by meta-data on the characteristics of studied patient cohorts and subjects (e.g., age, body weight, smoking status, health status), the applied interventions (e.g., dosing, substance, route of application), measured pharmacokinetic time-courses, and pharmacokinetic parameters (e.g., clearance, half-life, area under the curve). We demonstrate via multiple applications how the data set can be used to solidify existing knowledge and gain new insights relevant for metabolic phenotyping and liver function testing based on caffeine. Specifically, we analyzed 1) the alteration of caffeine pharmacokinetics with smoking and use of oral contraceptives; 2) drug-drug interactions with caffeine as possible confounding factors of caffeine pharmacokinetics or source of adverse effects; 3) alteration of caffeine pharmacokinetics in disease; and 4) the applicability of caffeine as a salivary test substance by comparison of plasma and saliva data. In conclusion, our data set and analyses provide important resources which could enable more accurate caffeine-based metabolic phenotyping and liver function testing.

Self-Medication of ADHD Symptoms: Does Caffeine Have a Role?

OBJECTIVE

Stimulants are the most effective treatment for Attention Deficit/ Hyperactivity disorder (ADHD). In addition, studies have shown that nicotine dependence in patients with ADHD is probably best explained by self-medication. The question is whether this is also true for caffeine use and caffeine dependence. The aim of our study was, therefore, to examine the relationship of ADHD symptoms, caffeine consumption, caffeine use disorder (CUD) and well-being. We hypothesized that those who have more ADHD symptoms and regularly consume caffeine have higher psychological well-being than those who have more ADHD symptoms, but do not consume caffeine.

METHODS

A general population sample (N = 2,259, 70.5% male, mean age 34.0) filled out the 10-item Caffeine Use Disorder Questionnaire (CUDQ), the Adult ADHD Self-report Scale (ASRS) and the WHO-5 Well-Being Index (WHO-5) and were asked about their caffeine consumption habits in an online survey.

RESULTS

There were no associations between ADHD and coffee, tea, energy drink or cola consumption or daily caffeine consumption. However, the results of the path analysis showed that the level of ADHD symptoms was positively associated with the level of CUD (β = 0.350) and negatively with the WHO-5 (β = -0.259).

CONCLUSIONS

Caffeine consumption was not associated with ADHD symptom severity and thus not likely to represent self-medication. On the contrary, caffeine use disorder severity is associated with more ADHD symptoms and both caffeine use disorder and ADHD are associated with lower well-being.

International society of sports nutrition position stand: caffeine and exercise performance

Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: 1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions. 2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals. 3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3-6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect. 4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session. 5. Caffeine appears to improve physical performance in both trained and untrained individuals. 6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation. 7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals. 8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. 9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4-6 mg/kg, respectively. 10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise. 11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.

The Effect of Coffee and Caffeine Consumption on Patients with Multiple Sclerosis-Related Fatigue

Background: Coffee and caffeine are considered to have beneficial effects in patients with multiple sclerosis (MS), an autoimmune disease of the central nervous system (CNS) that can lead to disability and chronic fatigue. Methods: In the present study the preference in terms of coffee and caffeine consumption in patients with MS was assessed. In total the opinions of 124 MS patients were explored with a questionnaire, which was developed to investigate the consumption behavior and associated beneficial and harmful effects of coffee and caffeine concerning symptoms of fatigue. Results: Our study showed that 37.1% of the included patients experience severe symptoms of fatigue. In our cohort, fatigue was not related to age, type of diagnosis or duration of the disease. The effects of coffee did not differ between MS patients with and without fatigue. Very few side effects linked to coffee consumption were reported, and we could demonstrate that coffee consumption had no negative impact on quality of sleep. A positive effect on everyday life was observed particularly among patients with a mid-level expanded disability status scale (EDSS). The strongest effects of coffee consumption were observed regarding a better ability to concentrate while fulfilling tasks, an expanded attention span and a better structured daily routine. Conclusions: Since coffee showed no severe side effects and in the absence of an effective fatigue therapy, coffee consumption might be a therapeutic approach for selected patients with MS-related fatigue.

Caffeine Uptake into the Vitreous after Peroral Coffee Consumption

INTRODUCTION

Caffeine and its metabolites have antioxidant activity, scavenging reactive oxygen species. The aim of our study was to measure caffeine concentrations in vitreous samples after peroral caffeine intake.

METHODS

This prospective study included patients scheduled for 23-G pars plana vitrectomy with membrane peeling due to epiretinal membranes. The study was performed in two parts: in the first part, patients were recruited into three different groups: group A consisted of habitual coffee drinkers who agreed to drink coffee containing 180 mg caffeine 1 h before surgery (n = 10), group B consisted of habitual coffee drinkers who were not offered coffee before surgery (n = 5), and group C consisted of non-habitual coffee drinkers, forming the control group (n = 5). In the second part (group D) patients (habitual coffee drinkers) agreed to give additional blood serum samples for measurement of caffeine concentration. Harvested samples of vitreous (groups A-D), epiretinal membranes (groups A-C), and blood serum samples (group D) were examined for concentrations of caffeine with gas chromatography-mass spectrometry.

RESULTS

Samples of 40 eyes of 40 patients were harvested. The concentrations of caffeine in the vitreous samples were 1,998 ± 967 ng/mL in group A and 1,108 ± 874 ng/mL in group B. In group C, caffeine concentrations were below 176 ng/mL in all vitreous samples. Both groups A and B had significantly higher concentrations of caffeine in the vitreous samples than group C (p < 0.002, p < 0.01, Mann-Whitney U test). Caffeine concentrations in epiretinal membranes were below the limits of detection. Correlation of caffeine concentrations between blood serum samples and vitreous samples in group D was high, with significantly higher caffeine concentrations in the blood serum.

CONCLUSION

Coffee consumption leads to significant caffeine levels in the vitreous compared to patients in the control group, and caffeine concentrations in the vitreous showed a high correlation to blood serum concentrations of caffeine after peroral coffee consumption.

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.

The Impact of Coffee and Caffeine on Multiple Sclerosis Compared to Other Neurodegenerative Diseases

Background: The literature concerning the effect of coffee and caffeine on Multiple Sclerosis (MS) with focus on fatigue is investigated in this review. Potentially clinically relevant effects were also assessed in studies concerning comparable neurodegenerative diseases, such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Since the existing studies obtained very inconclusive results, we systematically reviewed these studies to summarize the evidence on the possible effects of coffee and caffeine on those disease entities. Previous studies suggested that coffee and caffeine intake is associated with a reduced risk of developing MS and other neurological diseases.

Methods: The PubMed database was searched using the keywords “coffee” OR “caffeine” in combination with keywords for each of the different diseases. Besides the keyword search, we included studies by reference list search. Studies on the effects of coffee and caffeine on the single neurological diseases were included for this review. A total of 51 articles met our inclusion criteria. The reviewed articles assessed the impact of coffee and caffeine on the susceptibility for neurological diseases, as well as the effect of coffee and caffeine on disease progression and possible symptomatic effects like on performance enhancement.

Results: Higher intake of coffee and caffeine was associated with a lower risk of developing PD. In some of the MS studies there, is evidence for a similar effect and experimental studies confirmed the positive impact. Interestingly in MS coffee and caffeine may have a stronger impact on disease course compared to effects on disease susceptibility. In ALS no such beneficial effect could be observed in the clinical and experimental studies.

Conclusion: This literature assessment revealed that coffee and especially caffeine could have a preventative role in the development of several neurodegenerative diseases if provided in comparatively high doses. The systematic assessment indicates that coffee and caffeine intake must not be considered as a health risk. Additional clinical studies are needed to fully understand how far coffee and caffeine intake should be considered as a potential therapeutic approach for certain disease entities and conditions.

Mendelian Randomization Studies of Coffee and Caffeine Consumption

Habitual coffee and caffeine consumption has been reported to be associated with numerous health outcomes. This perspective focuses on Mendelian Randomization (MR) approaches for determining whether such associations are causal. Genetic instruments for coffee and caffeine consumption are described, along with key concepts of MR and particular challenges when applying this approach to studies of coffee and caffeine. To date, at least fifteen MR studies have investigated the causal role of coffee or caffeine use on risk of type 2 diabetes, cardiovascular disease, Alzheimer's disease, Parkinson's disease, gout, osteoarthritis, cancers, sleep disturbances and other substance use. Most studies provide no consistent support for a causal role of coffee or caffeine on these health outcomes. Common study limitations include low statistical power, potential pleiotropy, and risk of collider bias. As a result, in many cases a causal role cannot confidently be ruled out. Conceptual challenges also arise from the different aspects of coffee and caffeine use captured by current genetic instruments. Nevertheless, with continued genome-wide searches for coffee and caffeine related loci along with advanced statistical methods and MR designs, MR promises to be a valuable approach to understanding the causal impact that coffee and caffeine have in human health.

Adherence to the Caffeine Intake Guideline during Pregnancy and Birth Outcomes: A Prospective Cohort Study

The aims of this study were to identify: (i) the proportion of women exceeding the caffeine intake guideline (>200 mg/day) during each trimester, accounting for point of pregnancy awareness; (ii) guideline adherence trajectories across pregnancy; (iii) maternal characteristics associated with trajectories; and (iv) association between adherence and growth restriction birth outcomes. Typical and maximal intake per consumption day for the first trimester (T1; pre- and post-pregnancy awareness), second (T2), and third trimester (T3) were recorded for a prospective cohort of pregnant Australian women with singleton births (n = 1232). Birth outcomes were birth weight, small for gestational age, and head circumference. For each period, participants were classified as abstinent, within (≤200 mg), or in excess (>200 mg). Latent class growth analyses identified guideline adherence trajectories; regression analyses identified associations between adherence in each trimester and birth outcomes. The percentage of participants who reported caffeine use declined between T1 pre- and post-pregnancy awareness (89% to 68%), and increased in T2 and T3 (79% and 80%). Trajectories were: ‘low consumption’ (22%): low probability of any use; ‘within-guideline’ (70%): high probability of guideline adherence; and ‘decreasing heavy use’ (8%): decreasing probability of excess use. The latter two groups were more likely to report alcohol and tobacco use, and less likely to report planning pregnancy and fertility problems. Exceeding the guideline T1 pre-pregnancy awareness was associated with lower birth weight after covariate control (b = −143.16, p = 0.011). Overall, high caffeine intake pre-pregnancy awareness occurs amongst a significant minority of women, and continued excess use post-pregnancy awareness is more common where pregnancy is unplanned. Excess caffeine consumption pre-pregnancy awareness may increase the risk for lower birth weight. Increasing awareness of the guideline in pregnancy and preconception health care may be warranted.

Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption

Most individuals adjust their caffeine intake according to the objective and subjective effects induced by the methylxanthine. However, to reach the desired effects, the quantity of caffeine consumed varies largely among individuals. It has been known for decades that the metabolism, clearance, and pharmacokinetics of caffeine is affected by many factors such as age, sex and hormones, liver disease, obesity, smoking, and diet. Caffeine also interacts with many medications. All these factors will be reviewed in the present document and discussed in light of the most recent data concerning the genetic variability affecting caffeine levels and effects at the pharmacokinetic and pharmacodynamic levels that both critically drive the level of caffeine consumption. The pharmacokinetics of caffeine are highly variable among individuals due to a polymorphism at the level of the CYP1A2 isoform of cytochrome P450, which metabolizes 95% of the caffeine ingested. Moreover there is a polymorphism at the level of another critical enzyme, N-acetyltransferase 2. At the pharmacodynamic level, there are several polymorphisms at the main brain target of caffeine, the adenosine A2A receptor or ADORA2. Genetic studies, including genome-wide association studies, identified several loci critically involved in caffeine consumption and its consequences on sleep, anxiety, and potentially in neurodegenerative and psychiatric diseases. We start reaching a better picture on how a multiplicity of biologic mechanisms seems to drive the levels of caffeine consumption, although much more knowledge is still required to understand caffeine consumption and effects on body functions.

Caffeine intake is associated with pupil dilation and enhanced accommodation

PurposeIt is purported that caffeine, an autonomic stimulant, affects visual performance. This study sought to assess whether caffeine intake was associated with changes in pupil size and/or amplitude of accommodation.Patients and methodsA double-masked, crossover study was conducted in 50 healthy subjects of age range 19 to 25 years. Subjects were randomized to treatments such that subjects consumed either 250 mg caffeine drink or vehicle on separate days. Amplitude of accommodation was measured by the push-up technique, and pupil size using a millimeter ruler fixed to a slit lamp biomicroscope in dim illumination (5 lux). Amplitude of accommodation and pupil size were taken at baseline, and at 30, 60 and 90 min time points post treatment. Repeated measures one-way ANOVA and paired t-test were used in analyzing data.ResultsAmplitude of accommodation and pupil size after caffeine intake were significantly greater than vehicle (P<0.001) at each time point. Consumption of the caffeine beverage was associated with significant increases in amplitude of accommodation and pupil size with time (P<0.001). Amplitude of accommodation rose from 12.4 (±2.2 D) at baseline to 15.8(±2.6 D) at 90 min. Similarly, pupil size increased from 3.4 (±0.4 mm) at baseline to 4.5 (±0.72 mm) at 90 min. Consumption of vehicle was not associated with increase in amplitude of accommodation or pupil size with time.ConclusionPupil size and accommodation are affected after ingestion of caffeine. This study suggests caffeine may have some influence on visual functions.

Pharmacokinetic analysis and comparison of caffeine administered rapidly or slowly in coffee chilled or hot versus chilled energy drink in healthy young adults

Context: There is a paucity of data describing the impact of type of beverage (coffee versus energy drink), different rates of consumption and different temperature of beverages on the pharmacokinetic disposition of caffeine. Additionally, there is concern that inordinately high levels of caffeine may result from the rapid consumption of cold energy drinks. Objective: The objective of this study was to compare the pharmacokinetics of caffeine under various drink temperature, rate of consumption and vehicle (coffee versus energy drink) conditions. Materials: Five caffeine (dose = 160 mg) conditions were evaluated in an open-label, group-randomized, crossover fashion. After the administration of each caffeine dose, 10 serial plasma samples were harvested. Caffeine concentration was measured via liquid chromatography–mass spectrometry (LC–MS), and those concentrations were assessed by non-compartmental pharmacokinetic analysis. The calculated mean pharmacokinetic parameters were analyzed statistically by one-way repeated measures analysis of variance (RM ANOVA). If differences were found, each group was compared to the other by all pair-wise multiple comparison. Results: Twenty-four healthy subjects ranging in age from 18 to 30 completed the study. The mean caffeine concentration time profiles were similar with overlapping SDs at all measured time points. The ANOVA revealed significant differences in mean C_max and V_d ss/F, but no pair-wise comparisons reached statistical significance. No other differences in pharmacokinetic parameters were found. Discussion: The results of this study are consistent with previous caffeine pharmacokinetic studies and suggest that while rate of consumption, temperature of beverage and vehicle (coffee versus energy drink) may be associated with slightly different pharmacokinetic parameters, the overall impact of these variables is small. Conclusion: This study suggests that caffeine absorption and exposure from coffee and energy drink is similar irrespective of beverage temperature or rate of consumption.

Short-term effects of espresso coffee on heart rate variability and blood pressure in habitual and non-habitual coffee consumers--a randomized crossover study

OBJECTIVE

Coffee is one of the most widely consumed beverages worldwide. Aim of this study was to investigate short-term effects of espresso coffee on heart rate variability (HRV), a marker of vagal activity, in healthy habitual and non-habitual coffee consumers.

METHODS

Seventy-seven healthy subjects (38 habitual and 39 non-habitual coffee consumers, 74% women, mean age 26.97 ± 6.88 years) took part in three laboratory sessions in a randomized order. In condition 1, subjects consumed espresso; in condition 2, subjects consumed decaffeinated espresso; and in condition 3, subjects consumed warm water. HRV and blood pressure were assessed at rest before and after ingestion of the respective beverage.

RESULTS

HRV was significantly increased after consumption of caffeinated espresso, decaffeinated espresso, or water, indicating increased vagal activity in the course of the experiments. In the habitual coffee consumers, the increase in vagally mediated HRV was significantly lower after consumption of decaffeinated espresso compared to caffeinated espresso. Increases of systolic blood pressure were only found in the non-habitual consumers.

CONCLUSION

We found no evidence for specific short-term effects of caffeinated espresso on vagal activity in healthy subjects. Instead, consumption of decaffeinated espresso inhibited vagal activity in habitual consumers. This may be explained by an attempt of the organism to establish a sympathovagal equilibrium comparable to that after caffeine consumption. In the absence of caffeine-induced sympathetic activation, this may have been achieved by relative vagal withdrawal.

Caffeine delays autonomic recovery following acute exercise

BACKGROUND

Impaired autonomic recovery of heart rate (HR) following exercise is associated with an increased risk of sudden death. Caffeine, a potent stimulator of catecholamine release, has been shown to augment blood pressure (BP) and sympathetic nerve activity; however, whether caffeine alters autonomic function after a bout of exercise bout remains unclear.

METHODS

In a randomized, crossover study, 18 healthy individuals (26 ± 1 years; 23.9 ± 0.8 kg·m(-2)) ingested caffeine (400 mg) or placebo pills, followed by a maximal treadmill test to exhaustion. Autonomic function and ventricular depolarization/repolarization were determined using heart rate variability (HRV) and corrected QT interval (QTc), respectively, at baseline, 5, 15, and 30 minutes post-exercise.

RESULTS

Maximal HR (HRmax) was greater with caffeine (192 ± 2 vs. 190 ± 2 beat·min(-1), p < 0.05). During recovery, HR, mean arterial pressure (MAP), and diastolic blood pressure (DBP) remained elevated with caffeine (p < 0.05). Natural log transformation of low-to-high frequency ratio (LnLF/LnHF) of HRV was increased compared with baseline at all time points in both trials (p < 0.05), with less of an increase during 5 and 15 minutes post-exercise in the caffeine trial (p < 0.05). QTc increased from baseline at all time points in both trials, with greater increases in the caffeine trial (p < 0.05).

CONCLUSIONS

Caffeine ingestion disrupts post-exercise autonomic recovery because of increased sympathetic nerve activity. The prolonged sympathetic recovery time could subsequently hinder baroreflex function during recovery and disrupt the stability of autonomic function, potentiating a pro-arrhythmogenic state in young adults.

Removal of caffeine in sewage by Pseudomonas putida: Implications for water pollution index

A strain of Pseudomonas putida (biotype A) capable of growing on caffeine (1,3,7-trimethylxanthine) was isolated from a domestic wastewater processing operation. It used caffeine as the sole carbon source with a mean growth rate constant (k) of 0.049 h(-1) (approximately 20 h per generation), whereas k for glucose utilization under similar incubation conditions was 0.31 (3.3 h per generation). The isolate contained at least two plasmids, and the increased expression of a 40 kDa protein was attributable to growth on caffeine. Degradation byproducts of caffeine metabolism by the bacterial isolate included other xanthine derivatives. The slow bacterial catabolism of caffeine in sewage has implications for the effectiveness of wastewater purification, re-use and disposal.

Caffeine in tea Camellia sinensis--content, absorption, benefits and risks of consumption

Therapeutic properties of tea Camellia sinensis are of particular interest since it has been consumed for ages and was always regarded as safe beverage. Tea is most popular beverage in the world because of its attractive aroma, exceptional taste, health promoting and pharmaceutical potential. Current results showed that antioxidative, antibacterial and other health effects are attributed to its caffeine content and caffeine - polyphenols interactions. An overview is given on caffeine content in different tea leaves beverage. Special attention is drawn to caffeine physiological effect on human organism. Controversies concerning the possible caffeine influence on human physical and psychological health are briefly summarized and presented.

Maternal caffeine consumption and risk of congenital limb deficiencies

BACKGROUND

Animal studies have shown that high doses of caffeine might cause congenital limb deficiencies (LDs); however, no epidemiologic studies have explored this relation.

METHODS

This case-control study assessed associations between maternal dietary caffeine and congenital LDs using data from the National Birth Defects Prevention Study (NBDPS), with 844 LD cases and 8069 controls from 1997 to 2007. Caffeine intakes from beverages (coffee, tea, and soda) and chocolate combined and by beverage type were examined. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were estimated for subtypes of isolated LDs (no additional major anomalies) and LDs with other major anomalies separately, comparing the odds of 10 to <100, 100 to <200, 200 to <300, and 300+ mg/day total caffeine intake to 0 to <10 mg/day.

RESULTS

All total dietary caffeine intake categories of 10 mg/day and above were marginally associated with odds of all isolated LDs combined (aOR, 1.4-1.7), isolated longitudinal LDs (aOR, 1.2-1.6), and isolated transverse LDs (aOR, 1.3-1.8) compared to the lowest intake category. A dose-response pattern for total dietary caffeine intake was not observed.

CONCLUSIONS

A weak increased risk of congenital LDs associated with maternal dietary caffeine consumption was observed in this study; however, risk did not vary by amount of caffeine consumed.

Caffeine Use in Sports, Pharmacokinetics in Man, and Cellular Mechanisms of Action

Caffeine is the most widely consumed psychoactive 'drug' in the world and probably one of the most commonly used stimulants in sports. This is not surprising, since it is one of the few ergogenic aids with documented efficiency and minimal side effects. Caffeine is rapidly and completely absorbed by the gastrointestinal tract and is readily distributed throughout all tissues of the body. Peak plasma concentrations after normal consumption are usually around 50 microM, and half-lives for elimination range between 2.5-10 h. The parent compound is extensively metabolized in the liver microsomes to more than 25 derivatives, while considerably less than 5% of the ingested dose is excreted unchanged in the urine. There is, however, considerable inter-individual variability in the handling of caffeine by the body, due to both environmental and genetic factors. Evidence from in vitro studies provides a wealth of different cellular actions that could potentially contribute to the observed effects of caffeine in humans in vivo. These include potentiation of muscle contractility via induction of sarcoplasmic reticulum calcium release, inhibition of phosphodiesterase isoenzymes and concomitant cyclic monophosphate accumulation, inhibition of glycogen phosphorylase enzymes in liver and muscle, non-selective adenosine receptor antagonism, stimulation of the cellular membrane sodium/potassium pump, impairment of phosphoinositide metabolism, as well as other, less thoroughly characterized actions. Not all, however, seem to account for the observed effects in vivo, although a variable degree of contribution cannot be readily discounted on the basis of experimental data. The most physiologically relevant mechanism of action is probably the blockade of adenosine receptors, but evidence suggests that, at least under certain conditions, other biochemical mechanisms may also be operational.

Teratogen update: evaluation of the reproductive and developmental risks of caffeine

Caffeine is a methylated xanthine that acts as a mild central nervous system stimulant. It is present in many beverages, including coffee, tea, and colas, as well as chocolate. Caffeine constitutes 1-2% of roasted coffee beans, 3.5% of fresh tea leaves, and approximately 2% of mate leaves (Spiller, '84; Graham, '84a,b). Many over-the-counter medications, such as cold and allergy tablets, headache medicines, diuretics, and stimulants also contain caffeine, although they lead to relatively minimal intake (FDA, '86). In epidemiological studies, it is assumed that one cup of coffee contains < or =100 mg of caffeine, and soft drinks, such as colas, contain 10-50 mg of caffeine per 12-ounce serving. The per-capita consumption of caffeine from all sources is estimated to be about 3-7 mg/kg per day, or approximately 200 mg/day (Barone and Roberts, '96). Consumption of caffeinated beverages during pregnancy is quite common (Hill et al., '77) and is estimated to be approximately 144 mg/day, or 2.4 mg/kg for a 60-kg human (Morris and Weinstein, '81). However, pregnant women appear to consume slightly less than do other adults, approximately 1 mg/kg per day (Barone and Roberts, '96). This decrease may be interrelated with taste aversion (Hook, '76; Little, '82). The medical literature contains many varied references that appear to indicate that human adverse reproductive/developmental effects are produced by caffeine. If caffeine indeed causes such effects, the reproductive consequences could be very serious because caffeine-containing foods and beverages are consumed by most of the human populations of the world, and consumption in the United States is estimated to be 4.5-kg/person/year (Narod et al., '91). Therefore, the medical literature dealing with developmental and reproductive risks of caffeine was reviewed, and the biological plausibility of the epidemiological and animal findings, as well as the methods and conclusions of previous investigators, were evaluated. The epidemiological studies describe exposures of women to caffeine during pregnancy, as well as the occurrence of congenital malformations, fetal growth retardation, small-for-date babies, miscarriages (spontaneous abortions), behavioral effects, and maternal fertility problems that presumably resulted from the caffeine consumption. A few epidemiological studies were concerned with the genetic effects of preconception exposures to caffeine. Animal studies, conducted mostly in pregnant rats and mice, were designed to produce malformations. The objectives of the present review are to summarize the findings from the various clinical and animals studies, objectively discuss the merits and/or faults inherent in the studies and establish a global reproductive risk assessment for caffeine consumption in humans during pregnancy. It should be noted that evaluation of the developmental risks of caffeine based solely on epidemiological studies is difficult because the findings are inconsistent. Even more important, is the fact that caffeine users are subject to multiple confounding factors that make analyses difficult and prevent investigators from reaching definitive conclusions. For example, the caffeine content of foods and beverages can vary considerably, which can interfere with obtaining valid interpretations from many human studies. Isolated epidemiological studies dealing with the risk of abortion, without evaluating other developmental and reproductive effects, are the most difficult to interpret, because they present special problems that are sometimes ignored in epidemiological studies. The results of animal studies are probably most helpful in solving some of the dilemmas created by the epidemiological studies. An animal study reported in 1960 first focused our attention on the potential developmental effects of caffeine. However, the exposure reported by Nishimura and Nakai ('60) was an intraperitoneal dosage of 250 mg/kg in the mouse, an extremely high dosage that would result in a blood plasma level that could never be obtained from consuming caffeine containing products. More recent animal studies have demonstrated, that depending on the method of administration and species, the developmental NOEL in rodents is approximately 30 mg/kg per day, the teratogenic NOEL is 8,100 mg/kg per day, and the reproductive NOEL approximately 80-120 mg/kg per day. Lack of biological plausibility to support the concept that caffeine has been responsible for human malformations is another important part of this analysis. For example, no one has described the Caffeine "teratogenic syndrome," a cluster of malformations associated with caffeine ingestion. Proven human teratogens have an identifiable syndrome. The malformations described in the animal studies at very high doses fit the description of vascular disruptive types of malformations. (ABSTRACT TRUNCATED)

Are we dependent upon coffee and caffeine? A review on human and animal data

Caffeine is the most widely used psychoactive substance and has been considered occasionally as a drug of abuse. The present paper reviews available data on caffeine dependence, tolerance, reinforcement and withdrawal. After sudden caffeine cessation, withdrawal symptoms develop in a small portion of the population but are moderate and transient. Tolerance to caffeine-induced stimulation of locomotor activity has been shown in animals. In humans, tolerance to some subjective effects of caffeine seems to occur, but most of the time complete tolerance to many effects of caffeine on the central nervous system does not occur. In animals, caffeine can act as a reinforcer, but only in a more limited range of conditions than with classical drugs of dependence. In humans, the reinforcing stimuli functions of caffeine are limited to low or rather moderate doses while high doses are usually avoided. The classical drugs of abuse lead to quite specific increases in cerebral functional activity and dopamine release in the shell of the nucleus accumbens, the key structure for reward, motivation and addiction. However, caffeine doses that reflect the daily human consumption, do not induce a release of dopamine in the shell of the nucleus accumbens but lead to a release of dopamine in the prefrontal cortex, which is consistent with caffeine reinforcing properties. Moreover, caffeine increases glucose utilization in the shell of the nucleus accumbens only at rather high doses that stimulate most brain structures, non-specifically, and likely reflect the side effects linked to high caffeine ingestion. That dose is also 5-10-fold higher than the one necessary to stimulate the caudate nucleus, which mediates motor activity and the structures regulating the sleep-wake cycle, the two functions the most sensitive to caffeine. In conclusion, it appears that although caffeine fulfils some of the criteria for drug dependence and shares with amphetamines and cocaine a certain specificity of action on the cerebral dopaminergic system, the methylxanthine does not act on the dopaminergic structures related to reward, motivation and addiction.

The effect of caffeine on pregnancy outcome variables

The American public consumes a wide array of caffeinated products as coffee, tea, chocolate, cola beverages, and caffeine-containing medication. Therefore, it seems of value to inform both the scientific community and the consumer about the potential effects of excessive caffeine consumption, particularly by pregnant women. The results of this literature review suggest that heavy caffeine use (> or = 300 mg per day) during pregnancy is associated with small reductions in infant birth weight that may be especially detrimental to premature or low-birth-weight infants. Some researchers also document an increased risk of spontaneous abortion associated with caffeine consumption prior to and during pregnancy. However, overwhelming evidence indicates that caffeine is not a human teratogen, and that caffeine appears to have no effect on preterm labor and delivery. More research is needed before unambiguous statements about the effects of caffeine on pregnancy outcome variables can be made.

Caffeine effects on learning, performance, and anxiety in normal school-age children

OBJECTIVE

The purpose of this investigation was to study the acute effects of caffeine on learning, performance, and anxiety in normal prepubertal children.

METHOD

Twenty-one children were evaluated in a double-blind, placebo-controlled crossover design. Subjects were studied during four sessions, 1 week apart, under the following conditions: baseline, placebo, 2.5 mg/kg caffeine, and 5.0 mg/kg caffeine. Subjects were randomized to order of placebo and the two dosages of caffeine. Dependent measures included tests of attention, manual dexterity, short-term memory, and processing speed. Anxiety rating scales were also administered. Saliva samples were analyzed for caffeine levels.

RESULTS

Caffeine improved performance on two of four measures of the Test of Variables of Attention and on a test of manual dexterity in the dominant hand. There was a trend toward increased current level of self-reported anxiety after caffeine on a visual analogue measure of anxiety. Children reported feeling significantly less "sluggish" after caffeine ingestion than after placebo ingestion.

CONCLUSIONS

In a small sample size, there was indication that caffeine enhanced performance on a test of attention and on a motor task. Children also reported feeling less "sluggish" but somewhat more anxious. Because caffeine is so widely available and frequently consumed by children, these results are important and need replication.

Salivary caffeine and neonatal behavior: assay modification and functional significance

A radioimmunoassay (RIA) was developed for the quantification of caffeine in saliva. The mean salivary caffeine level for this sample of 40 full-term, AGA, healthy 1-2 day old human neonates was consistent with levels reported in previous studies. Salivary caffeine was significantly correlated with the number of state changes and startles observed during administration of the Brazelton Neonatal Behavior Assessment Scale. There was also a nonsignificant trend correlating salivary caffeine with visual orienting and consolability.

The clinical use and measurement of theophylline

This report reviews the clinical use, metabolism and toxicity of theophylline (Section 1). Current chromatographic and immunoassay methods for theophylline measurement are discussed and practical methods using high-performance liquid chromatography are described (Section 2). Results from the UK National scheme for theophylline quality control and from an experiment to investigate the degree of interference by 1,7-dimethylxanthine in routine assays for theophylline are discussed in Section 3.

Influence of alcohol and caffeine consumption on caffeine elimination

Ten healthy male volunteers were each studied on four separate occasions to assess the role of regular caffeine and alcohol intake on caffeine elimination. Antipyrine disappearance was also studied as an established quantitative test of hepatic microsomal function. Regular caffeine intake in high doses for 1 week failed to alter either antipyrine or caffeine pharmacokinetics. In contrast, alcohol intake of 50 g/day significantly prolonged caffeine half-life by 72% (P less than 0.005) and diminished caffeine clearance by 36% (P less than 0.0005). However, antipyrine kinetics were unaltered. These results demonstrate that alcohol, in amounts commonly consumed, is a strong inhibitor of caffeine metabolism.

The influence of fasting and of caffeine intake on finger tremor

The effect of finger tremor of the administration of 150 mg of caffeine three times daily for two days was measured using an accelerometer in 7 healthy subjects taking their normal diet (excluding caffeine-containing beverages). The effect on finger tremor of a short period of fasting with and without the 450 mg daily dose of caffeine was also studied in the same 7 subjects. Fasting increased finger tremor significantly when caffeine was administered. In doses comparable to the likely adult daily intake in this country, caffeine did not increase finger tremor whilst subjects were taking their normal diet.

Caffeine: implications of recent research for clinical practice

Caffeine is a central nervous system stimulant that has come under increasing scrutiny due to its effects on the health and mental health of those who consume it. This article summarizes the physiological effects of caffeine, reviews recent research on behavioral and mood changes associated with consumption, and discusses clinical implications for the mental health professional. Data on caffeine consumption and principal sources of caffeine are outlined.

Caffeine determination in rat plasma. A comparative study of micromethods

Confronted with the need for a sensitive (1 mg/1), specific and reproducible (less than 5%) method for the determination of caffeine in small plasma samples (10-50 microliter) of small laboratory animals, two existing methods, radioactive labelling and gas chromatography, were adapted. The first step, common to both methods, is chloroform extraction, followed by either gas-chromatographic analysis or radioactivity measurement. These methods were compared by using a common internal standard, labelled caffeine, measured before and after the extraction step. The initial requirements were fulfilled and the correlation of the results proved to be excellent. The methods can be extended to animals other than the rat, and to organs or biological fluids other than plasma. The very small amount of plasma needed for the determination allows pharmacokinetic studies to be conducted in small laboratory animals. Further, by combining the two methods it is possible to perform rather complex investigations, such as evaluating the extent of caffeine metabolism and, at the same time, determining levels in the case of chromic administration.

Effect of carbonated beverages and of an antiemetic containing carbohydrate and phosphoric acid on riboflavin bioavailability and salicylamide biotransformation in humans

Two carbohydrate-phosphoric acid solutions, one a widely used beverage (Solution C) and the other a pharmaceutical product used as an antiemetic (Solution E), administered together with riboflavin-5'-phosphate or salicylamide to healthy human adults, significantly increased the bioavailability of riboflavin and appreciably altered the metabolic fate of salicylamide (increased conversion to the sulfate and decreased formation of the glucuronide). A beverage containing phosphoric acid but no carbohydrates (Solution T) also increased the bioavailability of riboflavin but not as much as Solution C. These effects are attributed to a decrease of the gastric emptying rate caused by carbohydrates and phosphoric acid, consistent with the empirical use of Solution C syrup and Solution E as antinauseants and antiemetics. The results demonstrate also that the choice of beverage to be taken with medication can affect the bioavailability and/or metabolic fate of medicinals with saturable absorption and/or biotransformation characteristics.