Habitual Caffeine Consumption Research Articles

Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show?

Caffeine is a popular ergogenic aid that has a plethora of evidence highlighting its positive effects. A Google Scholar search using the keywords "caffeine" and "exercise" yields over 200,000 results, emphasizing the extensive research on this topic. However, despite the vast amount of available data, it is intriguing that uncertainties persist regarding the effectiveness and safety of caffeine. These include but are not limited to: 1. Does caffeine dehydrate you at rest? 2. Does caffeine dehydrate you during exercise? 3. Does caffeine promote the loss of body fat? 4. Does habitual caffeine consumption influence the performance response to acute caffeine supplementation? 5. Does caffeine affect upper vs. lower body performance/strength differently? 6. Is there a relationship between caffeine and depression? 7. Can too much caffeine kill you? 8. Are there sex differences regarding caffeine's effects? 9. Does caffeine work for everyone? 10. Does caffeine cause heart problems? 11. Does caffeine promote the loss of bone mineral? 12. Should pregnant women avoid caffeine? 13. Is caffeine addictive? 14. Does waiting 1.5-2.0 hours after waking to consume caffeine help you avoid the afternoon "crash?" To answer these questions, we performed an evidence-based scientific evaluation of the literature regarding caffeine supplementation.

Acute effects of energy drink on arterial stiffness and endothelial function in young male bodybuilders with habitual caffeine consumption

Elite bodybuilders consume energy drink (ED) immediately before or during strength training. However, the effects of ED on cardiovascular responses have not been fully understood. In this study, the carotid-femoral pulse wave velocity (cfPWV) and flow-mediated dilation (FMD), which are indices of arterial stiffness and endothelial function in response to acute ED consumption, were examined. Forty-five young men (30.0 ± 3.9 years) were investigated: sedentary (CON, n = 15), physically active (PA, n = 15), and bodybuilders (BD, n = 15). After they consumed commercial ED, their vascular function was analyzed at the following time points: pre, post, 30 min and 60 min. At baseline, the age, height and systolic and diastolic blood pressure of the groups did not significantly differ; conversely, their weight, body mass index, lean mass, fat percent and grip strengths significantly differed (p < 0.05). After ED consumption, central and peripheral blood pressure markedly increased in the PA and CON groups (p < 0.05) but not in the BD group. cfPWV, augmentation index and wave reflection were not different among the groups and did not change at any time point (p > 0.05). However, FMD notably differed among the groups after ED consumption. The FMD of the BD group increased sharply and significantly after ED consumption at post-time points (pre, 6.5% ± 1.7%; post, 13.1% ± 2.6%; 30 min, 10.7% ± 2.9%; 60 min, 8.9% ± 2.4%, p = 0.001). The FMD markedly increased after ED consumption in the PA group (p = 0.004), but it did not change in the CON group (p > 0.05). ED consumption acutely triggered the increase in endothelial function in the BD and PA groups. Therefore, these findings helped elucidate the distinct cardiovascular responses to ED intake among different populations with varying physical activity or training levels.

Genome-wide Association Study of Caffeine Consumption Using Coriell Personalized Medicine Collaborative Data

More than 90% of Americans consume caffeine daily, but the amount consumed varies widely. Previous studies have shown that genes related to caffeine metabolism and receptor binding may influence caffeine consumption. A better understanding of the relationship between genotype and caffeine consumption has the potential to inform mechanisms of this common dietary behavior. We performed a genome-wide association study (GWAS) of self-reported consumption data combining a wide range of caffeinated beverages including coffee, tea, soda, and energy drinks in the Coriell Personalized Medicine Collaborative (N=2,830) using a generalized linear model. Our analysis identified several candidate loci implicated in caffeine consumption. One previously identified SNP associated with caffeine consumption and replicated in the current study, rs2472297 (P-value=3.8x10-6), is located in an intergenic region between CYP1A1 and CYP1A2 (the gene that encodes the enzyme primarily responsible for caffeine metabolism), and has been associated with caffeine consumption in prior studies. Our results further support follow-up functional studies focused on the role of CYP1A1 and CYP1A2 on caffeine consumption habits, metabolism, and health status and outcomes.

ASSOCIATION BETWEEN CAFFEINE, ANXIETY AND THE OCCURRENCE OF APHTHOUS STOMATITIS IN THE ARMENIAN ETHNICITY

Abstract Introduction: Aphthous stomatitis is a recurring oral ulceration condition that affects a significant proportion of the population. While several factors have been proposed to contribute to its occurrence, the link between caffeine consumption, anxiety levels, and the development of aphthous stomatitis remains unknown. This survey-based study aimed to understand the association between coffee, anxiety, and the development of aphthous stomatitis in this specific demographic, which can provide useful insights for medical management as well as preventive strategies. Material and methods: A structured online questionnaire was distributed via various social media platforms targeting a sample of the Armenian population. The questionnaire collected information on participants’ demographics, coffee use patterns, anxiety levels as measured by perceived stress scales, and the occurrence of aphthous stomatitis. Statistical analyses, including Kendall’s tau, were carried out to investigate the relationships. Results: The results revealed a significant negative association between caffeine consumption and the occurrence of aphthous stomatitis among Armenian individuals Kendall’s tau-b (τb) correlation - 240* (p<0.05). Participants who reported regular caffeine consumption, such as coffee, tea, and energy drinks, had a lesser prevalence of aphthous stomatitis than non-consumers. Furthermore, Armenians in the survey showed that the majority (83.5%) had a low to moderate stress level. Conclusion: The data we collected in our research indicate that the prevalence of Recurrent Aphthous Stomatitis in the Armenian ethnicity was infrequent; over half of the participants didn’t report Recurrent Aphthous Stomatitis in the past 12 months. Which may correlate to their caffeine consumption habits, which can lead to stress reduction.

Secondary School Students and Caffeine: Consumption Habits, Motivations, and Experiences

Adolescents may be particularly vulnerable to the effects of caffeine due to a lack of tolerance, their small size, changing brain physiology, and increasing independence. Concerns about adolescent caffeine consumption relate to potentially serious physiological and psychological effects following consumption. Motivations driving caffeine intake are not well understood among adolescents but are important to understand to reduce harmful behavioural patterns. This study explored caffeine consumption habits (sources, amount, frequency) of New Zealand adolescents; and factors motivating caffeine consumption and avoidance. The previously validated caffeine consumption habits questionnaire (CaffCo) was completed by 216 participants (15-18 years), with most (94.9%) consuming at least one caffeinated product daily. Chocolate, coffee, tea, and kola drinks were the most consumed sources. The median caffeine intake was 68 mg·day-1. Gender (boy) and being employed influenced the source, but not the quantity of caffeine consumed. One-fifth (21.2%) of adolescents consumed more than the recommended European Food Safety Authority (EFSA) safe level (3 mg·kg-1·day-1). Taste, energy, and temperature were the main motivators for consumption, and increased energy, excitement, restlessness, and sleep disturbances were reported effects following caffeine consumption. This study provides information on caffeinated product consumption among New Zealand adolescents, some of whom consumed caffeine above the EFSA safe level. Public health initiatives directed at adolescents may be important to reduce potential caffeine-related harm.

Caffeine and sport.

Caffeine is a trimethylxanthine found in coffee and several other foods and beverages. Its stimulatory effects make it an interesting strategy to boost performance for athletic populations. Scientific evidence supports its efficacy to improve high-intensity endurance exercise, explosive and high-intensity efforts, resistance exercise, team sports and combat sports, though individual variation in the ergogenic response to caffeine exists. Supplementation can be taken in many forms including dissolved in water, via capsules, coffee, energy drinks and caffeinated gum; ingestion via capsules, dissolved in water or in caffeinated gum appear to be most effective. Variability in the exercise response following caffeine supplementation may be explained by genetic factors or habitual caffeine consumption. Caffeine is an excellent supplement for athletes looking to improve their exercise performance, though some consideration of side-effects and impact on sleep are warranted.

Caffeine and Team ball performances: A Mini-Review

Background: Caffeine is the most consumed psychoactive substance globally, second only to water in beverage consumption. Its impact on athletic performance, particularly in team sports, has been a subject of growing research interest. This review focuses on recent studies investigating caffeine's influence on various aspects of team ball sports performance. Objectives: This mini-review aimed to (i) synthesize current research findings on caffeine supplementation in team sports, considering different doses, forms, and its effects across genders and (ii) to highlight key considerations for optimal caffeine use in these sports. Methods: THIS mini-review examined recent studies on caffeine's effects in team ball sports, analyzing variables such as supplementation strategies, habitual consumption, gender, washout periods, individual responses, and supplement forms (capsules or powders). The focus is on studies that have used caffeine doses ranging from 3 to 6 mg·kg -1, administered 60 minutes before competition. Results: Findings suggest beneficial effects of caffeine ingestion (3 to 6 mg·kg-1) in enhancing technical and physical aspects of team ball sports. However, results vary based on factors like the supplementation strategy, individual caffeine consumption habits, and gender. Most research has focused on single-dose effects, revealing a lack of comprehensive, gender-specific guidelines for caffeine's optimal use in team sports. Conclusion: While caffeine supplementation shows promise in enhancing team sports performance, there is a need for more comprehensive research, especially regarding gender-specific effects and optimal consumption strategies. Current evidence points to the potential benefits of caffeine in morning competitions or training sessions but indicates possible detrimental effects in afternoon or evening settings. Further research is needed to develop robust guidelines for caffeine use in team sports, considering dosage, timing, form, and differential gender effects.

Assessment of caffeine consumption behavior among Jazan University students in the south of Saudi Arabia: A cross-sectional study

Caffeine is a central nervous system stimulant. High consumption levels of caffeine can lead to intoxication and serious side effects. Saudi Arabia is witnessing a rise in the commercialization and consumption of caffeine. Young adults such as university students may exhibit high levels of caffeine consumption. This investigation aims to assess caffeine consumption habits among a sample of Jazan University students in the south of Saudi Arabia. This study was a cross-sectional investigation that utilized multistage sampling to recruit the students. Data was collected via a self-administered questionnaire that measured student demographics, their frequency of consuming caffeine-containing food, portion sizes, and patterns of consumption during different times of the day. Caffeine consumption levels were estimated based on a cutoff point of 400 mg per day. A chi-squared test was used to investigate the association between levels of caffeine consumption and measured study characteristics. A sample of 964 students was recruited with a mean age of 21.8 years. The most frequently consumed product among the recruited students was coffee (32%), followed by chocolate bars (16%) and soft drinks (12%). The median total consumed caffeine amount was 185 mg per day. 194 (20%) students of the sample exceeded the recommended level of daily caffeine consumption (>400 mg/day). Among the measured demographics, only the year of study was associated with caffeine consumption (P value of .003), suggesting that students in their earlier years of university are likely to exceed the recommended daily consumption of caffeine in comparison with those who are in their later years of study. Our investigation identified high levels of caffeine consumption among some students. The findings imply the need to enhance the awareness of students who exceed the recommended daily intake of caffeine regarding the harmful impacts of caffeine toxicity.

Variability of caffeine content in green and roasted Coffea arabica regarding the origin, post-harvest processing, and altitude, and overview of recommended daily allowance

Caffeine content is a crucial attribute of coffee. Its concentration and thus maximum cups of Coffea arabica from Africa, Asia, Central America, and South America from different altitudes of growing areas, altitude, and process using different post-harvest processing (dry, wet, and pulped natural). Our results suggest that geographical origin might affect the alkaloid concentration in C. arabica. The caffeine concentration pattern in green samples was as follows: Central America > South America > Asia > Africa. Altitude affected the concentrations, lowlands > midlands > highlands, however, not significantly. Given caffeine is thermostable, the medium roasting process did not affect the concentration of caffeine directly, but a small increase was observed. Scientific opinion on the safety of habitual caffeine consumption of up to 400 mg per day does not raise safety concerns for non-pregnant adults. A cup (7 g coffee in 120 mL of water) was used for recalculation. Results suggest that mostly highlands and midlands coffee from Africa reached levels of caffeine that might be consumed in more than 5.5 cups a day.

Relationship between genetic polymorphisms of cytokines and self-reported sleep complaints and habitual caffeine consumption

Pro-inflammatory cytokines are involved in sleep-wake regulation and are associated with caffeine consumption. This is a cross-sectional study in 1023 active French workers investigating associations between self-reported sleep complaints (>3months) and total sleep time (TST) with nine single-nucleotide-polymorphisms (SNPs) including pro-inflammatory cytokines, according to caffeine consumption. Participants were characterized as low, moderate and high (0–50, 51–300, and >300 mg/day) caffeine consumers. After adjusting the odd ratios (OR) for age, gender, and smoking, the risk of sleep complaints was higher in subjects with genetic mutations in tumor necrosis factor alpha (TNF-α, rs 1800629) (ORa [95%CI] = 1.43 [1.07–1.92] for both G/A and A/A aggregate genotypes) or interleukin-1 beta (IL-1β, rs1143627) (ORa = 1.61 [1.08–2.44] for homozygous A/A genotype), and the risk was higher when subjects carry the mutations in TNF-α plus IL-1β regardless of caffeine consumption. When stratified with caffeine consumption, the risk of sleep complaints was higher in TNF-α A allele carriers in high caffeine consumers, and in homozygous A/A genotype of IL-1β in moderate and high consumers. None of the nine SNPs influence TST, with the exception of the mutation on CYP1A2 and only when stratified with caffeine consumption. Our results also indicated more caffeine side-effects when carrying mutation on IL1β. This study showed that polymorphisms in TNF-α and/or IL-1β influenced sleep complaints but did not influence total sleep time. This suggests that management of sleep complaints, which can be addressed by clinical interventions, should consider the influence of the genetic profile of pro-inflammatory cytokines.

The characteristics of caffeine intake in Croatian university students

Abstract Background Excessive caffeine intake combined with increasing numbers and availability of caffeine-containing products in modern societies are causes for concern. University students may be at increased risk of excessive caffeine consumption due to seeking caffeinated products with well-known wakefulness effects and cognitive benefits. This study aimed to highlight the characteristics of caffeine consumption among Croatian university students. Methods This cross-sectional questionnaire study was conducted from May 2020 to April 2021 period. A validated, anonymous questionnaire that contained questions regarding demographic data, data about caffeine consumption habits, and its sources was self-administered via an online link to a cross-faculty representative student sample of the University of Osijek in Eastern Croatia. Results The study sample included 1197 subjects with, median age of 22 years (interquartile range 21-24), 24.1% males, and 75.9% females. The median caffeine intake was 512.0 mg/day (interquartile range 228.0-972.0). The higher caffeine intake was observed in part-time students (p = 0.026), students who were preparing for exams during the participation in this study (p = 0.010), and students who smoked cigarettes (p < 0.001). There was a poor positive correlation between the amount of caffeine intake and academic success connected with caffeine consumption (rs = 0.225; p < 0.001). There were fair positive correlations between the amount of caffeine intake and caffeine consumption because of the avoidance of the withdrawal symptoms (rs = 0.490; p < 0.001) and between the amount of caffeine intake and knowledge of the impact of caffeine consumption on the occurrence of social conflicts (rs = 0.349; p < 0.001). Conclusions The study revealed high caffeine intake among Croatian university students. The implementation of specific preventive measures directed toward the protection of students’ health from adverse health effects related to caffeine is needed. Key messages • Croatian university students have displayed high caffeine intake in their everyday life. • There is a need for the implementation of specific preventive measures directed toward the protection of students’ health from adverse health effects related to caffeine consumption.

Reply to Zhang and Chen’s Comment on “Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine”

Reply to Zhang and Chen’s Comment on “Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine”

Comment on “Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine”

Comment on “Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine”

Cardiometabolic Biomarkers and Habitual Caffeine Consumption Associate with the Adverse Ambulatory Blood Pressure Response to Strenuous Physical Exertion among Firefighters.

Caffeine has beneficial effects on firefighter job performance reducing fatigue and improving psychomotor vigilance. However, excessive caffeine intake may raise blood pressure (BP) following a bout of acute exercise among adults with elevated BP. The influence of caffeine intake on the ambulatory BP (ABP) response to vigorous physical exertion among firefighters has not been studied. In this sub-study we conducted secondary statistical analyses from a larger clinical trial (NCT04514354) that included examining the influence of habitual caffeine intake, and cardiometabolic biomarkers shown to influence BP, on the ABP response following a bout of sudden vigorous exertion over 19 h among firefighters. Previously, we found high amounts of calcium and sodium intake raised BP following a bout of acute exercise among adults with elevated BP. Thus, other secondary aims were to examine the influence of habitual calcium and sodium intake, and cardiometabolic biomarkers have shown to influence BP, on the ABP response following sudden vigorous exertion over 19 h among firefighters. Firefighters (n = 15) completed a Food-Frequency Questionnaire assessing habitual dietary intake over the past year. They randomly completed a maximal graded exercise stress test (GEST) and non-exercise CONTROL on separate non-workdays leaving the laboratory wearing an ABP monitor for 19 h. Prior to and immediately after the GEST, fasting venous blood was collected to measure lipid-lipoproteins, c-reactive protein, and blood glucose. Height and weight were taken to calculate body mass index. Repeated measures ANCOVA tested if the ABP response differed after GEST vs. CONTROL. Linear mixed models examined the relationships among caffeine, calcium, sodium, cardiometabolic biomarkers, and the ABP response following GEST vs. CONTROL. Firefighters were middle-aged (40.2 ± 9.5 year), overweight (29.0 ± 3.9 kg/m2) men with elevated BP (124.1 ± 10.3/79.6 ± 11.5 mmHg) who consumed 542.0 ± 348.9 mg of caffeine/day, about ~50% more than the dietary reference intake. Unexpectedly, systolic ABP was higher by 18.0 ± 6.7 mmHg and diastolic ABP by 9.1 ± 5.4 mmHg (ps < 0.01) over 19 h following GEST vs. CONTROL. We found 24% of the variance in the adverse ABP response to maximal physical exertion was explained by caffeine intake, and when combined with c-reactive protein, non-high-density lipoprotein-cholesterol, body mass index, blood glucose, and resting heart rate, up to 74% of the variability in the ABP response was explained. Additionally, we found calcium (ps < 0.001) and sodium (p < 0.0001) intake each explained up to 24% of the ABP response. Further investigation is needed in a larger, more diverse sample of firefighters to better establish how caffeine contributes to the adverse BP response to strenuous physical exertion.

No Influence Of Habitual Caffeine Consumption On Its Ergogenic Effects: A Systematic Review And Meta-analysis.

Caffeine can improve exercise capacity and performance, although there appears to be substantial inter-individual variation in the performance response following caffeine intake. There is contrasting evidence as to whether habitual caffeine consumption influences the acute response to caffeine supplementation. PURPOSE: To quantify the proportion of the literature on caffeine supplementation that reports habitual caffeine consumption and determine its influence on the acute exercise response to caffeine supplementation using a systematic review and meta-analytic approach. METHODS: MedLine, Embase, and SPORTDiscus were searched, and articles were screened for inclusion/exclusion criteria. Random-effects meta-analyses and meta-regression models were used to examine the influence of habitual caffeine consumption on the overall ergogenic effects of caffeine and on different types of exercise types (endurance, strength, power). Subanalyses - were performed by acute relative dose (< 3, 3-6, > 6 mg/kg body weight), by whether the acute caffeine dose was lower or higher than the average daily caffeine dose, and by caffeine withdrawal time before the intervention (< 24, 24-48, > 48 h). RESULTS: Fifty-two (18%) of 289 caffeine studies contained sufficient information on habitual caffeine consumption to be included in the meta-analysis. There was a positive overall effect of caffeine compared with placebo (SMD=0.23, 95%CI: 0.19-0.28; p<0.001), with relative habitual caffeine consumption having no effect (p=0.99). Sub-analyses showed a significant ergogenic effect when the caffeine dose was <3 mg/kgBM (SMD=0.19, 95%CI: 0.09-0.29; p=0.004) and 3-6 mg/kgBM (SMD=0.25, 95%CI: 0.20-0.30; p<0.001), but not >6 mg/kgBM (SMD=0.12, 95%CI: -0.04-0.27; p = 0.10); when the dose was both higher (SMD=0.23, 95%CI: 0.18-0.28; p<0.001) and lower (SMD=0.19, 95%CI: 0.01-0.38; p=0.04) than the habitual caffeine dose; and when withdrawal was <24h, 24-48h and >48h. Caffeine was effective for endurance, strength and endurance training, with no influence of relative habitual caffeine consumption within exercise types (all p>0.05). CONCLUSION: Habitual caffeine consumption does not appear to influence the acute ergogenic effects of caffeine.

Higher and lower caffeine consumers: exercise performance and biological responses during a simulated soccer-game protocol following caffeine ingestion.

Research on whether caffeine habituation reduces its ergogenicity is scarce and conflicting. The purpose of the present study was to examine the influence of habitual caffeine consumption on exercise performance and biological responses during a simulated soccer-game protocol following acute caffeine ingestion. Twenty professional male soccer players were categorized as higher (n = 9) or lower caffeine consumers (n = 11) after answering a validated questionnaire. Participants performed a simulated treadmill soccer-game protocol on treadmill following either caffeine (6mg kg-1) or placebo ingestion, during which several variables were evaluated. Time to exhaustion, countermovement jump height, mean arterial pressure, heart rate, plasma glucose, and lactate were higher (P ≤ 0.001), while rating of perceived exertion (RPE) was lower (P = 0.002), following caffeine compared to placebo ingestion, with no differences between groups (P > 0.05). Plasma non-esterified fatty acids exhibited a higher response to caffeine in the higher vs lower caffeine consumers. Reaction time, plasma glycerol and epinephrine, carbohydrate and fat oxidation, and energy expenditure were not affected by caffeine (P > 0.05). Caffeine ingestion largely improved cardiovascular and neuromuscular performance, while reducing RPE, in both higher and lower caffeine consuming athletes during prolonged intermitted exercise to exhaustion.

Caffeine intake exerts dual genome-wide effects on hippocampal metabolism and learning-dependent transcription.

Caffeine is the most widely consumed psychoactive substance in the world. Strikingly, the molecular pathways engaged by its regular consumption remain unclear. We herein addressed the mechanisms associated with habitual (chronic) caffeine consumption in the mouse hippocampus using untargeted orthogonal omics techniques. Our results revealed that chronic caffeine exerts concerted pleiotropic effects in the hippocampus at the epigenomic, proteomic, and metabolomic levels. Caffeine lowered metabolism-related processes (e.g., at the level of metabolomics and gene expression) in bulk tissue, while it induced neuron-specific epigenetic changes at synaptic transmission/plasticity-related genes and increased experience-driven transcriptional activity. Altogether, these findings suggest that regular caffeine intake improves the signal-to-noise ratio during information encoding, in part through fine-tuning of metabolic genes, while boosting the salience of information processing during learning in neuronal circuits.

Can I Have My Coffee and Drink It? A Systematic Review and Meta-analysis to Determine Whether Habitual Caffeine Consumption Affects the Ergogenic Effect of Caffeine.

The aim was to quantify the proportion of the literature on caffeine supplementation that reports habitual caffeine consumption, and determine the influence of habitual consumption on the acute exercise response to caffeine supplementation, using a systematic review and meta-analytic approach. Three databases were searched, and articles screened according to inclusion/exclusion criteria. Three-level meta-analyses and meta-regression models were used to investigate the influence of habitual caffeine consumption on caffeine's overall ergogenic effect and within different exercise types (endurance, power, strength), in men and women, and in trained and untrained individuals. Sub-analyses were performed according to the following: acute relative dose (< 3, 3-6, > 6mg/kg body mass [BM]); whether the acute caffeine dose provided was lower or higher than the mean daily caffeine dose; and the caffeine withdrawal period prior to the intervention (< 24, 24-48, > 48h). Sixty caffeine studies included sufficient information on habitual consumption to be included in the meta-analysis. A positive overall effect of caffeine was shown in comparison to placebo (standard mean difference [SMD] = 0.25, 95% confidence interval [CI] 0.20-0.30; p < 0.001) with no influence of relative habitual caffeine consumption (p = 0.59). Subgroup analyses showed a significant ergogenic effect when the caffeine dose was < 3mg/kg BM (SMD = 0.26, 95% CI 0.12-0.40; p = 0.003) and 3-6mg/kg BM (SMD = 0.26, 95% CI 0.21-0.32; p < 0.0001), but not > 6mg/kg BM (SMD = 0.11, 95% CI - 0.07 to 0.30; p = 0.23); when the dose was both higher (SMD = 0.26, 95% CI 0.20-0.31; p < 0.001) and lower (SMD = 0.21, 95% CI 0.06-0.36; p = 0.006) than the habitual caffeine dose; and when withdrawal was < 24h, 24-48h, and > 48h. Caffeine was effective for endurance, power, and strength exercise, with no influence (all p ≥ 0.23) of relative habitual caffeine consumption within exercise types. Habitual caffeine consumption did not modify the ergogenic effect of caffeine in male, female, trained or untrained individuals. Habitual caffeine consumption does not appear to influence the acute ergogenic effect of caffeine.

Caffeine Supplementation Strategies Among Endurance Athletes.

Caffeine is widely accepted as an endurance-performance enhancing supplement. Most scientific research studies use doses of 3–6 mg/kg of caffeine 60 min prior to exercise based on pharmacokinetics. It is not well understood whether endurance athletes employ similar supplementation strategies in practice. The purpose of this study was to investigate caffeine supplementation protocols among endurance athletes. A survey conducted on Qualtrics returned responses regarding caffeine supplementation from 254 endurance athletes (f = 134, m =120; age = 39.4 ± 13.9 y; pro = 11, current collegiate athlete = 37, recreational = 206; running = 98, triathlon = 83, cycling = 54, other = 19; training days per week = 5.4 ± 1.3). Most participants reported habitual caffeine consumption (85.0%; 41.2% multiple times daily). However, only 24.0% used caffeine supplements. A greater proportion of men (31.7%) used caffeine supplements compared with women (17.2%; p = 0.007). Caffeine use was also more prevalent among professional (45.5%) and recreational athletes (25.1%) than in collegiate athletes (9.4%). Type of sport (p = 0.641), household income (p = 0.263), education (p = 0.570) or working with a coach (p = 0.612) did not have an impact on caffeine supplementation prevalence. Of those reporting specific timing of caffeine supplementation, 49.1% and 34.9% reported consuming caffeine within 30 min of training and races respectively; 38.6 and 36.5% used caffeine 30–60 min before training and races. Recreational athletes reported consuming smaller amounts of caffeine before training (1.6 ± 1.0 mg/kg) and races (2.0 ± 1.2 mg/kg) compared with collegiate (TRG: 2.1 ± 1.2 mg/kg; RACE: 3.6 ± 0.2 mg/kg) and professional (TRG: 2.4 ± 1.1 mg/kg; RACE: 3.5 ± 0.6 mg/kg) athletes. Overall, participants reported minor to moderate perceived effectiveness of caffeine supplementation (2.31 ± 0.9 on a four-point Likert-type scale) with greatest effectiveness during longer sessions (2.8 ± 1.1). It appears that recreational athletes use lower caffeine amounts than what has been established as ergogenic in laboratory protocols; further, they consume caffeine closer to exercise compared with typical research protocols. Thus, better education of recreational athletes and additional research into alternative supplementation strategies are warranted.

Cerebral hemodynamic response to caffeine: effect of dietary caffeine consumption.

Caffeine has a significant effect on cerebrovascular systems, and the dual action of caffeine on both neural and vascular responses leads to concerns for the interpretation of blood oxygenation level-dependent (BOLD) functional MRI. However, potential differences in the brain response to caffeine with regard to consumption habits have not been fully elucidated, as BOLD responses may vary with the dietary caffeine consumption history. The main aim of this study was to characterize the acute effect of caffeine on cerebral hemodynamic responses in participants with different patterns of caffeine consumption habits. Fifteen non-habitual and 11 habitual volunteers were included in this study. The cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) to the breath-hold challenge were measured before and after 200 mg caffeine administration. The non-habitual individuals exhibited a pattern of progressive reduction in CBF with time. The CVR was diminished in the caffeinated condition (P < 0.05). In the habitual group, the pattern of CBF decrease was smaller and homogeneous across the brain, and reached steady state rapidly. The CVR was not affected in the presence of caffeine (P > 0.05). Our results demonstrated that the cerebral hemodynamic response to caffeine was subject to the habitual consumption patterns of the participants. The compromised CVR following caffeine administration in the non-habitual group may partially explain the suppressed BOLD response to a visual stimulation in low-caffeine-level users.