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Effects of caffeine on energy metabolism, heart rate, and methylxanthine metabolism in lean and obese women
Abstract
The magnitude of coffee-induced thermogenesis and the influence of coffee ingestion on substrate oxidation were investigated in 10 lean and 10 obese women, over two 24-h periods in a respiratory chamber. On one occasion the subjects consumed caffeinated coffee and on the other occasion, decaffeinated coffee. The magnitude of thermogenesis was smaller in obese (4.9 +/- 2.0%) than in lean subjects (7.6 +/- 1.3%). The thermogeneic response to caffeine was prolonged during the night in lean women only. The coffee-induced stimulation of energy expenditure was mediated by a concomitant increase in lipid and carbohydrate oxidation. During the next day, in postabsorptive basal conditions, the thermogenic effect of coffee had vanished, but a significant increase in lipid oxidation was observed in both groups. The magnitude of this effect was, however, blunted in obese women (lipid oxidation increased by 29 and 10% in lean and obese women, respectively). Caffeine increased urinary epinephrine excretion. Whereas urinary caffeine excretion was similar in both groups, obese women excreted more theobromine, theophylline, and paraxanthine than lean women. Despite the high levels of urinary methylxanthine excretion, thermogenesis and lipid oxidation were less stimulated in obese than in lean subjects.
... O consumo de alimentos que possuem em sua estrutura compostos bioativos pode influenciar modestamente o equilíbrio de energia, alterando gasto energético, oxidação de substratos, e / ou a sensação de fome [13,14]. Esta alternativa no tratamento da obesidade e/ou controle de peso é eficaz, pois a perda de peso, mesmo quando modesta, reduz o risco de mortalidade e morbidade em indivíduos com excesso de peso e leva a efeitos benéficos à saúde [15,16]. Um alimento que apresenta em sua estrutura bioativos importantes é a pimenta vermelha. ...
... Artigos encontrados Artigos utilizados Red pepper and obesity 16 2 Red pepper and satiety 3 1 Red pepper and thermogenesis 7 2 ...
Introdução: As pimentas vermelhas são frutos membros do gênero Capsicum. Seus principais compostos bioativos são denominados capsaicinóides. Atualmente tem sido proposto que esses compostos possuem propriedades que podem trazer efeitos benéficos para a saúde. Objetivo: Analisar estudos de intervenção com objetivo de verificar os efeitos do consumo de pimenta vermelha no emagrecimento e no controle de peso. Metodologia: Foram realizadas diferentes buscas em uma base de dados (Pubmed) 86 artigos foram localizados, dos quais oito foram selecionados para esta revisão. Resultados: Dos oito artigos incluídos, seis demonstraram efeitos benéficos do consumo da pimenta vermelha no emagrecimento ou controle de peso. Foi observado que o consumo de pimenta vermelha aumenta o gasto energético pós-prandial. Foi observada a influência do consumo de pimenta vermelha na termogênese induzida pela dieta, oxidação de substratos, aumento da saciedade e redução do consumo energético. O mecanismo de ação ainda não é completamente esclarecido, embora seja proposto que a maioria destes efeitos seja resultado da estimulação do sistema nervoso simpático. Conclusão: Sugere-se que existem evidências de que a pimenta vermelha pode desempenhar um papel benéfico no emagrecimento e controle de peso.Palavras-chave: pimenta vermelha, emagrecimento, termogênese, obesidade.
... In vitro and in vivo studies discovered that caffeine increased the expression of thermogenesis-related genes such as PGC-1α and mitochondrial biogenesis, as well as levels of UCP1 in brown adipocytes [84]. Another study involving lean and obese individuals demonstrated that caffeine led to increased energy expenditure and lipid oxidation [85]. Additionally, a focused study observed that caffeine treatment resulted in increased expression of UCP1 and thermogenic genes in BAT, indicating the potential for BAT activation [86]. ...
Brown and beige adipocytes are renowned for their unique ability to generate heat through a mechanism known as thermogenesis. This process can be induced by exposure to cold, hormonal signals, drugs, and dietary factors. The activation of these thermogenic adipocytes holds promise for improving glucose metabolism, reducing fat accumulation, and enhancing insulin sensitivity. However, the translation of preclinical findings into effective clinical therapies poses challenges, warranting further research to identify the molecular mechanisms underlying the differentiation and function of brown and beige adipocytes. Consequently, research has focused on the development of drugs, such as mirabegron, ephedrine, and thyroid hormone, that mimic the effects of cold exposure to activate brown fat activity. Additionally, nutritional interventions have been explored as an alternative approach to minimize potential side effects. Brown fat and beige fat have emerged as promising targets for addressing nutritional imbalances, with the potential to develop strategies for mitigating the impact of metabolic diseases. Understanding the influence of nutritional factors on brown fat activity can facilitate the development of strategies to promote its activation and mitigate metabolic disorders.
... However, weight loss observed with yerba mate consumption has been previously attributed to the caffeine content of the tea, which has been demonstrated to make up 1-2% of dry leaf weight [38]. As a stimulant, caffeine has been shown to increase basal metabolic rate, improve aerobic performance and muscle oxygen content during exercise tests [39], and increase lipid oxidation [40,41]. Additionally, caffeine has been reported to increase the in vivo and in vitro expression of adipose UCP1 (uncoupling protein 1), a mitochondrial uncoupling protein that releases energy stored in the mitochondrial proton gradient in the form of heat, in brown adipose [42]. ...
Yerba maté, an herbal tea derived from Ilex paraguariensis, has previously been reported to be protective against obesity-related and other cardiometabolic disorders. Using high-resolution respirometry and reverse-phase high-performance liquid chromatography, the effects of four weeks of yerba maté consumption on mitochondrial efficiency and cellular redox status in skeletal muscle, adipose, and liver, tissues highly relevant to whole body metabolism, were explored in healthy adult mice. Yerba maté treatment increased mitochondrial oxygen consumption in adipose, but not in other tissues examined. Yerba maté increased ATP concentration in skeletal muscle and decreased ATP concentration in adipose. Combined with observed changes in oxygen consumption, these data yielded a significantly higher ATP:O2, a measure of mitochondrial efficiency, in muscle and a significantly lower ATP:O2 in adipose, which were consistent with yerba maté-induced weight loss. Yerba maté treatment also altered the hepatic glutathione (GSH)/glutathione disulfide (GSSG) redox potential to a more reduced redox state, suggesting potential protective effects against oxidative stress and preservation of cellular function. Together, these data indicate beneficial, tissue-specific effects of yerba maté supplementation on mitochondrial bioenergetics and redox states in healthy mice that are protective against obesity.
... Combining sibutramine with stimulants such as amphetamines can further enhance the effects and potentially increase the risk of cardiovascular problems [44]. When taken together, sibutramine and caffeine may have additive stimulant effects. ...
The use of dietary supplements (DSs) has dramatically increased in recent decades. However, around 20% of these products are reported to contain pharmacologically active undeclared compounds, most of which could expose consumers to serious side effects. According to recent data, some of the most commonly detected undeclared compounds are also considered doping and are prohibited by the World Anti-Doping Agency (WADA). One of the most frequently detected undeclared substances in DSs used for promoting weight loss is sibutramine. In 2011, all medicines containing sibutramine were urgently withdrawn from Europe and US markets because of serious side effects. In the present study, in order to detect and quantify sibutramine in DSs, a rapid, sensitive, and reliable gas chromatography with mass spectrometry (GC-MS) method was developed. The method was validated according to the ICH guidelines and demonstrated good linearity, accuracy, precision, and robustness. The limits of detection and quantification were 0.181 μg/mL and 0.5488 μg/mL, respectively. The method was applied to analyze 50 DSs promoting weight loss, fat burning, and performance enhancement. Sibutramine was detected in six of them in a range of 16.59–14,854.94 μg/per capsule. The high concentrations of sibutramine detected in some samples raise concerns about the potential health risks associated with the use of adulterated DSs. The proposed GC-MS method could be used successfully in the quality control of DSs or in different research programs, contributing to safety and the prevention of associated side effects.
... Capsinoids exert similar effects in increasing BAT-dependent energy expenditure as does cold exposure (Luo et al. 2012). Caffeine (1,3,7-trimethylxantine), a widely consumed plant alkaloid found in coffee, and tea has been shown to aid weight loss and increased energy expenditure in both human and animals, thus reducing the risk of type 2 diabetes (Bukowiecki et al. 1983, Dulloo et al. 1989, Astrup et al. 1990, Bracco et al. 1995, Kobayashi-Hattori et al. 2005, Bhupathiraju et al. 2013. By using a stem cell model of adipocyte browning (Velickovic et al. 2018) a physiological amount of caffeine was shown to promote UCP1 function (Velickovic et al. 2019). ...
... Estos mecanismos podrían reforzar el hecho que el café y la cafeína ayudan en la reducción de peso. No obstante, este efecto se ha visto reducido en los pacientes con obesidad (29) . Por eso mismo, no se considera útil agregar cafeína a un producto y venderlo como coadyuvante para bajar de peso. ...
El café es la sustancia psicoactiva más consumida en el mundo, con múltiples propiedades beneficiosas. En esta investigación se revisan estudios sobre los efectos del café y la cafeína en la salud. Se realizó una revisión bibliográfica de revisiones sistemáticas y artículos originales de diversas bases de datos relacionados al café y la cafeína. Se encontraron estudios sobre el café y sus efectos en el sistema nervioso central, digestivo y cardiovascular. Asimismo, se revisan las formas del consumo de café como descafeinado, instantáneo y molido. Aunque agrava la gastritis, disminuye la absorción ósea de calcio, aumenta la presión arterial y reduce la biodisponibilidad del hierro; el café también es un antiinflamatorio, disminuye el apetito, aumenta la diuresis y alivia la cefalea.
... The ability of caffeine to stimulate SNS activity, and thus, thermogenesis, is due to its ability to inhibit PDE and allow the accumulation of cAMP, as well as induce an increase in lipolysis, which makes caffeine a primary ingredient in many thermogenic supplements. Caffeine alone has been shown to increase metabolic rate in trained and untrained males and females at various moderate doses [13][14][15][16][17][18][19][20]. Similar to the findings of the present study, multiple studies have demonstrated that metabolic rate was moderately increased in both normal weight [13,14,19] and clinically obese [14,20] women for a short period. ...
Background
Thermogenic supplements are widely used in the general population to support attempted fat loss; however, the efficacy and safety of these supplements are questioned.
Purpose
To determine whether a thermogenic supplement affects metabolic rate, hemodynamic responses, and mood states.
Methods
In a randomized double-blind crossover design, 23 females (22.2 ± 3.5 years; 164.8 ± 6.4 cm; 73.5 ± 6.9 kg) who were moderate caffeine consumers (<150 mg/day) reported to the lab after a 12 h fast for baseline assessments of resting energy expenditure (REE) via indirect calorimetry, heart rate (HR), blood pressure (SBP and DBP), blood variables, and hunger, satiety, and mood states. Thereafter, subjects ingested the assigned treatment (active treatment containing caffeine, micronutrients, and phytochemicals [TR] or placebo [PL]). All variables were reassessed at 30-, 60-, 120-, and 180 min post-ingestion. Subjects repeated the same protocol with ingestion of the opposite treatment on a separate day. All data were analyzed using a 2 × 5 ANOVA with repeated measures and significance was accepted a priori at p < 0.05.
Results
In the TR group, mean increases in REE of 121 to 166 kcal/d were observed at 30-, 60-, and 180 min post-ingestion (p < 0.01 for all). PL group mean decreases in REE of 72 to 91 kcal/day were observed at 60-, 120-, and 180 min (p < 0.05 for all). Respiratory quotient decreased at 120 and 180 min in both treatments. Slight increases in SBP of 3–4 mmHg were observed at 30, 120, and 180 min (p < 0.05 for all) post-ingestion of TR, while no effects were observed for DBP. Observed increases in SBP were within normal blood pressure ranges. TR decreased subjective fatigue with no other significant changes in mood states. Glycerol was maintained in TR, while there was a decrease at 30, 60, and 180 min (p < 0.05 for all) post-ingestion of PLA. Free fatty acids increased in TR at 60 and 180 min (p < 0.05) post-ingestion as well as a significant difference between treatments at 30 min post-ingestion indicating greater circulating free fatty acids levels in TR vs. PL (p < 0.01).
Conclusion
These findings indicate that ingestion of a specific thermogenic supplement formulation produces a sustained increase in metabolic rate and caloric expenditure and reduces fatigue over 3 h without producing adverse hemodynamic responses.
استهدفت هذه الدراسة اختبار تأثير المستخلص الإيثانولي المائي لأوراق نبات المرسين على الغدة الدرقية وهرموناتها في الجرذان البيضاء ، حيث استخدمت جرعة بتركيز 2 جرام/كجم وأعطيت للجرذان عن طريق الفم . وشملت هذه الدراسة عدد 43 جرذ قسمت إلى ثلاث مجموعات ، المجموعة الأولى تم ذبحها بعد 7 أيام والمجموعة الثانية تم ذبحها بعد 14 يوم من بداية المعاملة ، أما المجموعة الثالثة فقد قسمت إلى 5 مجاميع صغيرة تم ذبحها بعد 2 و 4 و 8 و 12 ساعة من بداية المعاملة ، واشتملت كل مجموعة على بعض الجرذان كمجموعة ضابطة .
بين الفحص المورفولوجي في هذه الدراسة ظهور بعض الأعراض المرضية على الجرذان المعاملة بالمستخلص تمثلت في حدوث نزف في الفم والأنف وعند الأطراف ، كما لوحظ على هذه الحيوانات الهزال والتعب وفقدان الشهية للأكل بعد حوالي 72 ساعة من بداية المعاملة ، إضافة إلى حدوث انخفاض معنوي في وزن الجرذان . وقد أظهرت نتائج الاختبارات الهرمونية للمصل حدوث ارتفاع معنوي في مستوى هرمونات الغدة الدرقية والهرمون المحفز لإفرازها في الجرذان المعاملة بالمستخلص لمدة أسبوع وأسبوعين .
وعلى مستوى الفحص النسيجي ازدادت الجريبات الدرقية زيادة ملحوظة في الحجم ، وخاصة الجريبات المتواجدة في أطراف الغدة . وامتلأت العديد من الجريبات بتجمعات من المادة الغروية غير المتجانسة التي ازدادت الفجوات عند أطرافها ، كما ظهرت بعض الخلايا الإلتهابية داخل المادة الغروية لبعض الجريبات . وأصبحت الجريبات غير منتظمة الحدود ، وظهرت الخلايا الجريبية بصورة منضغطة وذات أنوية مسطحة ، إضافة إلى وجود بعض الجريبات غير محددة المعالم .
Accurate resting metabolic rate readings are essential for dietary planning and body composition monitoring not only for healthy individuals but also for athletes. A number of factors can alter resting metabolic rate during its measurement by indirect calorimetry. The methodology used may affect the results of the study. A clear standardisation of this procedure is needed to obtain the most accurate results.
Purpose: To review the literature to determine the optimal subject condition and methodology for the resting metabolism measurement procedure using indirect calorimetry.
Materials and methods: A literature search was conducted in PubMed, MEDLINE and Cochrane Library databases. The query included key words and logical phrases: “calorimetry”, “indirect calorimetry”, “resting metabolic rate”, “energy metabolism”, “basal metabolism”, “standards”. Only Englishlanguage studies and human studies were considered. Additional information was identified because of the review and included in the review.
Results: the parameters of standardization during the resting metabolism measurement procedure are described: consumption of food, ethanol, caffeine, nicotine; daily activities and physical activity; body position in space and environmental conditions during the measurement; actions of the specialist performing the procedure, etc. The article outlines effective methods for measuring resting metabolism to obtain the most accurate results in both athletes and non-athletes.
Conclusion: an attempt has been made to formulate precise methodological rules for standardization and recommendations for measuring resting metabolism by indirect calorimetry.
Accurate resting metabolic rate readings are essential for dietary planning and body composition monitoring not only for healthy individuals but also for athletes. A number of factors can alter resting metabolic rate during its measurement by indirect calorimetry. The methodology used may affect the results of the study. A clear standardisation of this procedure is needed to obtain the most accurate results.
Purpose: To review the literature to determine the optimal subject condition and methodology for the resting metabolism measurement procedure using indirect calorimetry.
Materials and methods: A literature search was conducted in PubMed, MEDLINE and Cochrane Library databases. The query included key words and logical phrases: “calorimetry”, “indirect calorimetry”, “resting metabolic rate”, “energy metabolism”, “basal metabolism”, “standards”. Only English-language studies and human studies were considered. Additional information was identified because of the review and included in the review.
Results: the parameters of standardization during the resting metabolism measurement procedure are described: consumption of food, ethanol, caffeine, nicotine; daily activities and physical activity; body position in space and environmental conditions during the measurement; actions of the specialist performing the procedure, etc. The article outlines effective methods for measuring resting metabolism to obtain the most accurate results in both healthy individuals and athletes.
Conclusion: an attempt has been made to formulate precise methodological rules for standardisation and recommendations for measuring resting metabolism by indirect calorimetry.
Several studies report a substantial rise in plasma catecholamines after caffeine. Epinephrine infusion induces a pressor response after nonselective -blockade. We studied the hemodynamic and humoral effects of drinking coffee after placebo and after both nonselective (propranolol) and 1-selective (metoprolol) blockade in 12 normotensive subjects. After placebo, coffee induced a rise in systolic and diastolic blood pressure and a fall in heart rate, whereas forearm blood flow did not change. Plasma catecholamines, especially epinephrine (+150%), rose and plasma renin activity, fell after drinking coffee. The effects of coffee on blood pressure, forearm blood flow, and all humoral parameters were not altered by pretreatment with propranolol or metoprolol. The fall in heart rate after coffee, however, seemed to be greater during propranolol. We conclude that the rise in plasma epinephrine after coffee was too small to reveal differences in reaction in propranolol- and metoprolol-pretreated subjects.
Single-dose oral administration of 100 mg caffeine increased the resting metabolic rate of both lean and postobese human volunteers by 3-4% (p less than 0.02) over 150 min and improved the defective diet-induced thermogenesis observed in the postobese subjects. Measurements of energy expenditure (EE) in a room respirometer indicate that repeated caffeine administration (100 mg) at 2-h intervals over a 12-h day period increased the EE of both subject groups by 8-11% (p less than 0.01) during that period but had no influence on the subsequent 12-h night EE. The net effect was a significant increase (p less than 0.02) in daily EE of 150 kcal in the lean volunteers and 79 kcal in the postobese subjects. Caffeine at commonly consumed doses can have a significant influence on energy balance and may promote thermogenesis in the treatment of obesity.
The overall thermogenic response to food intake measured over a whole day in 20 young nondiabetic obese women (body fat mean ± SEM: 38.6 ± 0.7%), was compared with that obtained in eight nonobese control women (body fat: 24.7 ± 0.9%). The energy expenditure of the subjects was continuously measured over 24 h with a respiration chamber, and the spontaneous activity was assessed by a radar system. A new approach was used to obtain the integrated thermogenic response to the three meals ingested over the day (from 8:30 AM to 10:30 PM). This method allows to subtract the energy expended for physical activity from total energy expenditure and to calculate the integrated dietary-induced thermogenesis as the difference between the energy expended without physical activity and basal metabolic rate. The thermogenic response to the three meals (expressed in percentage of the total energy ingested) was found to be blunted in obese women (8.7 ± 0.8%) as compared with that of controls ( 14.8 ± 1.1 %). There was an inverse correlation between the percentage body fat and the diet-induced thermogenesis (r = −0.61, p < 0.001). In addition, the relative increase in diurnal urinary norepinephrine excretion was lower in obese than in the control subjects. It is concluded that a low overall thermogenic response to feeding may be a contributing factor for energy storage in some obese subjects; a blunted response of the sympathetic nervous system could explain this low thermogenic response.
The purpose of this investigation was to study the sparing effects of caffeine on the utilization of muscle glycogen during 30 min of leg ergometer cycling (70% V̇O 2 max). A caffeine solution (250 ml; 5 ml/kg body weight) ingested 1 h prior to exercise (CAF trial) decreased the use of muscle glycogen by 42% (P < 0.025) in seven subjects when compared to a decaffeinated control trial (CON). There was a modest increase in serum FFA and muscle triglyceride use was 150% greater in the CAF as compared to the CON trial. Respiratory exchange during exercise also reflected a shift in carbon source from carbohydrate to lipid. Since known in vitro effects of caffeine include an increased use of muscle lipid and an inhibitory influence on phosphorylase a, it is suggested that the ergogenic effects of caffeine on endurance performance are, in part, the result of direct actions in muscle rather than solely to enhanced mobilization, uptake, and oxidation of blood-borne FFA.
The effect of coffee, decaffeinated coffee and a control beverage on plasma FFA was studied in a group of normal human subjects. The effect of caffeine sodium benzoate was also studied in the dog. Significant elevations in FFA were observed after coffee and caffeine which usually reached their peak in 3 or 4 hours. The administration of sucrose significantly reduced the immediate FFA response. The FFA effects with decaffeinated coffee were markedly less than with regular coffee and were similar to that of the control beverage. These effects are considered to be of importance, particularly in that they may be related to other disturbances in lipid metabolism.
Using a double-blind, randomized, cross-over protocol, we studied the effect of a single dose of oral caffeine on plasma renin activity, catecholamines and cardiovascular control in nine healthy, young, non-coffee drinkers maintained in sodium balance throughout the study period. Caffeine (250 mg) or placebo was administered in a methylxanthine-free beverage to overnight-fasted supine subjects who had had no coffee, tea or cola in the previous three weeks. Caffeine increased plasma renin activity by 57 per cent, plasma norepinephrine by 75 per cent and plasma epinephrine by 207 per cent. Urinary normetanephrine and metanephrine were increased 52 per cent and 100 per cent respectively. Mean blood pressure rose 14/10 mm Hg one hour after caffeine ingestion. There was a slight fall and then a rise in heart rate. Plasma caffeine levels were usually maximal one hour after ingestion but there was considerable individual variation. A 20 per cent increase in respiratory rate correlated well with plasma caffeine levels. Under the conditions of study caffeine was a potent stimulator of plasma renin activity and adrenomedullary secretion. Whether habitual ingestion has similar effects remains to be determined.
The wide variations in urinary bladder and colo-rectal cancer incidence in humans have been attributed in part to metabolic factors associated with exposure to carcinogenic aromatic and heterocyclic amines. Cytochrome P-4501A2 (CYP1A2), which catalyses N-oxidation, and acetyltransferase (NAT2) which catalyses N- and O-acetylation, both appear to be polymorphically distributed in human populations; and slow and rapid NAT2 phenotypes have been implicated as risk factors for these cancers. Caffeine has also been shown to undergo 3-demethylation by CYP1A2, and it is further acetylated to 5-acetylamino-6-formylamino-3-methyluracil (AFMU) by the polymorphic NAT2. In this report, we describe a metabolic phenotyping procedure that can be used to determine concomitantly the hepatic CYP1A2 and NAT2 phenotypes. For the NAT2 phenotype, we confirm the valid use of the urinary molar ratio of AFMU/1-methylxanthine, even in alkaline urines. For the CYP1A2 phenotype, the urinary molar ratio of [1,7-dimethylxanthine + 1,7-dimethyluric acid]/caffeine, taken at 4-5 h after caffeine ingestion, was identified from pharmacokinetic analyses of 12 subjects as being better correlated (r = 0.73; p = 0.007) with the rate constant for caffeine 3-demethylation than other previously suggested ratios. This procedure was then used to determine the CYP1A2 phenotype in subjects from Arkansas (n = 101), Italy (n = 95), and China (n = 78). Statistical and probit analyses of nonsmokers indicated that the CYP1A2 activity was not normally distributed and appeared trimodal. This trimodality allowed arbitrary designation of slow, intermediate, and rapid phenotypes, which ranged from 12-13% slow, 51-67% intermediate, and 20-37% rapid, in the different populations. A reproducibility study of 13 subjects over a 5 day or 5 week period showed that, with one exception, intraindividual variability did not alter this CYP1A2 phenotypic classification. Induction of CYP1A2 by cigarette smoking was also confirmed by the increased caffeine metabolite ratios observed in the Arkansas and Italian smokers (blonde tobacco). However, Italian smokers of black tobacco and Chinese smokers did not appear to be induced. Furthermore, probit analyses of Arkansas and Italian blonde tobacco smokers could not discriminate between phenotypes, apparently as a consequence of enzyme induction.
Urinary excretion of caffeine in two populations (men and women) of cyclotourists was measured, at rest and during exercise, after oral administration of 350 mg of caffeine in aqueous solution. The so-called "total metabolites", as measured by the EMIT test, were also determined, as well as urinary creatinine. At rest, elimination in relation to body weight was identical in men and women. During exercise a fivefold decrease in the female and twofold decrease in the male populations were observed. After exercise, caffeine elimination was greater than during the physical trial but remained lower for women than for men. "Total metabolites" excretion showed evidence for a slowing of caffeine catabolism during exercise and a restart of it after exercise. The caffeine content of beverages varies considerably from one country to another, depending on local customs, so that caffeine intake may be highly variable. Our results lead us to query the validity of the upper authorized official limit for urinary caffeine (12 micrograms.ml-1) in doping controls. The nature of the sporting event, sex, weight, and sampling delay after exercise are all factors that argue against the utilization of a unique standard.
The effect of moderate exercise on the kinetics of caffeine in 12 healthy volunteers-6 heavy coffee drinkers (HD) and 6 light coffee drinkers (LD) has been studied. Kinetics at Rest was measured first (R): the subjects remained at rest for 8 h after a single 250 mg dose of caffeine. One week later, the Exercise Kinetics (E) was measured under the same conditions, but with the subjects performing moderate exercise (30% of VO2 max) during the first hour of the study.
Exercise raised the maximal plasma caffeine concentrations (R: 7.28; E: 10.45) and reduced both the half-life (R 3.99 h; E 2.29 h) and the volume of distribution (R 371; E 20.91). Both during exercise and at rest, HD had a greater half-life elimination and volume of distribution than LD.
The results suggest potentiation of the effects of caffeine during exercise and an increase in its distribution due to regular heavy coffee intake.
Because it has previously been shown that it takes much more caffeine to cause fat mobilization in vitro than in vivo, it has been suggested that there may be an active metabolite working with caffeine causing an increase in lipolysis in vivo. To determine the relationship between the appearance of paraxanthine (caffeine's major dimethylxanthine metabolite) and free fatty acid (FFA) mobilization after intravenous caffeine administration, 10 men were studied at rest after receiving a dose of 4 mg/kg lean body mass. Venous blood samples were obtained before dosing and at minutes 5, 10, 15, 30, 45, 60, 90, 120, 150, and 180. Serum levels of FFA, glycerol, caffeine, and paraxanthine were determined in duplicate. Concentrations of FFA and glycerol were corrected for plasma volume changes. A high negative correlation was seen between decreases in caffeine and increases in FFA (r = -0.90) and a high positive correlation was seen between the appearance of paraxanthine and FFA (r = 0.93). It was concluded that paraxanthine may play a role in increased lipolysis after caffeine administration in humans.