Doses Of Caffeine Research Articles

Motor improvement in Parkinson's disease patients receiving caffeine adjuvants: A double-blind randomized controlled trial in Indonesia.

Parkinson's disease (PD) manifests as a movement and brain function disorder characterized by symptoms such as resting tremors, rigidity, bradykinesia, and postural instability, leading to disability among patients. The use of psychostimulants such as caffeine has been associated with the improvement of motor symptoms in PD patients; however, studies regarding the effect of caffeine adjuvant therapy on motor function among PD patients in the Indonesian population are lacking. The aim of this study was to evaluate motor improvement as measured by the change in scores of the Movement Disorder Society - Unified Parkinson's Disease Rating Scale Part III (MDS-UPDRS-III) among PD patients receiving caffeine adjuvant. A double-blind randomized controlled trial (RCT) was conducted among PD patients at Dr. Soetomo General Academic Hospital and Universitas Airlangga Hospital, Surabaya, Indonesia, from April to August 2023. A total of 27 patients were enrolled and randomly assigned to an intervention (receiving caffeine adjuvant, n=15) and control group (receiving placebo, n=12). Motor improvement was measured using the UPDRS III score prior to intervention and three weeks after. The Chi-squared test was used to analyze the difference in UPDRS III scores between the two groups. Motor improvement, as demonstrated by a reduction in the UPDRS III score, was observed in patients receiving caffeine adjuvant compared to those receiving placebo (80.0% vs 16.7%; p=0.004). Regarding the safety profile, only four out of 15 (26.6%) patients treated with caffeine reported minor adverse events. These conditions improved over time during the intervention. None of the 12 patients in the placebo reported adverse events. This study provides valuable insights into the initial dosage of caffeine that improves motor function in PD patients with minimum adverse effects.

Investigation into the Effects of Caffeine on Reaction Time

How reaction time changed depending on dose of caffeine consumed was investigated by conducting an experiment where participants drank different quantities of coffee each day and measured their reaction time using a website that asked the user to tap the screen when it turned green. This was measured every 30 minutes for 7 hours after the caffeine had been fully consumed. Graphs were plotted for the results obtained and regression fits were added to analyse the data. The observed trends were that reaction time decreased when caffeine consumption was increased, which correlated with expected results. The highest administered dose deviated from this trend, however, was put down to a ‘caffeine crash’ that was experienced by the participants.Important factors that were considered when discussing the results were pre-established caffeine tolerances as well as the diversity within the sample of participants.

Potential of high dose caffeine citrate to cause intracranial hemorrhage in a premature rat model

Potential of high dose caffeine citrate to cause intracranial hemorrhage in a premature rat model

The Analgesic and Anti-inflammatory Properties of Caffeine Co-administration with Nefopam in Mice

This study aimed to evaluate the analgesic properties of nefopam and the adjuvant effects of caffeine. It also investigated the anti-inflammatory effect of co-administering nefopam and caffeine on Prostaglandin E2 level (PGE2). The study involved 56 female albino mice (Mus musculus), divided into seven groups, eight mice per each group. Group A which served as the control group received distilled water; Group B received 30 mg/kg BW of nefopam orally; Group C received 28.5 mg/BW of nefopam and 5 mg/BW of caffeine orally; Group D received 27 mg/BW of nefopam and 10 mg/BW of caffeine orally; Group E received 25.5 mg/BW of nefopam and 15 mg/BW of caffeine orally; Group F received 24 mg/BW of nefopam and 20 mg/BW of caffeine orally; Group G received 22.5 mg/BW of nefopam and 25 mg/BW of caffeine orally. The nociceptive response was assessed using the formalin test, showing a significant (P<0.05) reduction in pain response (accumulative time of flinching and licking) was the first phase (0-5 minutes) in Group E as well as, a significant (P<0.05) decrease in nociceptive response in flinching and licking in second phase (20-60 minutes) was observed in Group D. However, the Prostaglandin level was significantly (P<0.05) lower in Group C. The study concluded that adding low dosages of caffeine to analgesics can boost pain relief in smaller quantities. Caffeine co-administration with nefopam may exert

Warm-up music and low-dose caffeine enhance the activity profile and psychophysiological responses during simulated combat in female taekwondo athletes

To assess the effects of warm-up music and low dose (3 mg·kg−1) of caffeine (CAF) on female taekwondo athlete’s activity profile and psychophysiological responses during simulated combat. In a double-blinded, randomized, crossover study, 16 female athletes participated in simulated combats under one control and 5 experimental conditions [i.e., CAF alone (CAF), placebo alone (PL), CAF with music (CAF + M), PL with music (PL + M), and no supplement with music (M)]. After warming-up, athletes rated their felt arousal (FAS). Mean (HRmean) and peak (HRpeak) heart rate values were determined for each combat. After fighting, athletes rated their perceived exertion (RPE), feeling scale (FS), FAS, and physical enjoyment (PACES). Time-motion and technical-tactical variables were analyzed. CAF + M induced shorter skip and pause time, while attack time increased compared to other conditions (p < 0.05). Moreover, CAF + M increased single attacks, combined attacks, counter-attacks (p < 0.001), and defensive actions (p < 0.05) than other conditions. HRmean and HRpeak were lower under CAF + M than other conditions (p < 0.05). Additionally, higher FAS post-combat, FS, and PACES were observed under CAF + M, while RPE was lower (except CAF condition) compared to the other conditions (p < 0.05.Using CAF with warm-up music may increase combat cadence and improve the psychological state in female athletes more effectively than either strategy alone.

When to sleep and consume caffeine to boost alertness.

Sleep loss can cause cognitive impairments that increase the risk of mistakes and accidents. However, existing guidelines to counteract the effects of sleep loss are generic and are not designed to address individual-specific conditions, leading to suboptimal alertness levels. Here, we developed an optimization algorithm that automatically identifies sleep schedules and caffeine-dosing strategies to minimize alertness impairment due to sleep loss for desired times of the day. We combined our previous algorithms that separately optimize sleep or caffeine to simultaneously identify the best sleep schedules and caffeine doses that minimize alertness impairment at desired times. The optimization algorithm uses the predictions of the well-validated Unified Model of Performance to estimate the effectiveness and physiological feasibility of a large number of possible solutions and identify the best one. To assess the optimization algorithm, we used it to identify the best sleep schedules and caffeine-dosing strategies for four studies that exemplify common sleep-loss conditions and compared the predicted alertness-impairment reduction achieved by using the algorithm's recommendations against that achieved by following the U.S. Army caffeine guidelines. Compared to the alertness-impairment levels in the original studies, the algorithm's recommendations reduced alertness impairment on average by 63%, an improvement of 24 percentage points over the U.S. Army caffeine guidelines. We provide an optimization algorithm that simultaneously identifies effective and safe sleep schedules and caffeine-dosing strategies to minimize alertness impairment at user-specified times.

Effects of Acute Guarana (Paullinia cupana) Ingestion on Mental Performance and Vagal Modulation Compared to a Low Dose of Caffeine.

Guarana (GUA), a Brazilian seed extract, contains caffeine and other bioactive compounds that may have psychoactive effects. To assess the acute effects of GUA compared to a low dose of caffeine (CAF) on cognitive and mood parameters, twenty participants completed a double-blind, crossover experiment where they ingested capsules containing the following: (1) 100 mg CAF, (2) 500 mg GUA containing 130 mg caffeine, or (3) placebo (PLA). Cognitive tests (Simon and 2N-Back Task) were performed at the baseline (pre-ingestion) and 60 min after ingestion. The response time for the cognitive tests and heart rate variability were unaffected (p > 0.05) by treatment, although 2N-Back was overall faster (p = 0.001) across time. The accuracy in the 2N-Back Task showed a significant interaction effect (p = 0.029) due to higher post-ingestion versus pre-ingestion levels (p = 0.033), but only with the PLA. The supplements also had no effect on cognitive measures following physical fatigue (n = 11). There was an interaction effect on perceived mental energy, where the pre-ingestion of GUA had lower mental pep ratings compared to post-ingestion (p = 0.006) and post-exercise (p = 0.018) levels. Neither the acute ingestion of GUA nor low dose of CAF influenced cognitive performance or provided consistent benefit on mood or mental workload through vagal modulation. Additional investigations are beneficial to determining the lowest effective dose for CAF or GUA to influence mood and/or cognitive performance.

Effect of caffeine ingestion on time trial performance in cyclists: a systematic review and meta-analysis.

Caffeine, widely recognized as an ergogenic aid, has undergone extensive research, demonstrating its effectiveness to enhance endurance performance. However, there remains a significant gap in systematically evaluating its effects on time trial (TT) performance in cyclists. This meta-analysis aimed to determine the efficacy of caffeine ingestion to increase cycling TT performance in cyclists and to evaluate the optimal dosage range for maximum effect. A search of four databases was completed on 1 December 2023. The selected studies comprised crossover, placebo-controlled investigations into the effects of caffeine ingestion on cycling TT performance. Completion time (Time) and mean power output (MPO) were used as performance measures for TT. Meta-analyses were performed using a random-effects model to assess the standardized mean differences (SMD) in individual studies. Fifteen studies met the inclusion criteria for the meta-analyses. Subgroup analysis showed that moderate doses of caffeine intake (4-6 mg/kg) significantly improved cycling performance (SMD Time = -0.55, 95% confidence interval (CI) = -0.84 ~ -0.26, p < 0.01, I2 = 35%; SMD MPO = 0.44, 95% CI = 0.09 ~ 0.79, p < 0.05, I2 = 39%), while the effects of low doses (1-3 mg/kg) of caffeine were not significant (SMD Time = -0.34, 95% CI = -0.84 ~ 0.17, p = 0.19, I2 = 0%; SMD MPO = 0.31, 95% CI = -0.02 ~ 0.65, p = 0.07, I2 = 0%). A moderate dosage (4-6 mg/kg) of caffeine, identified as the optimal dose range, can significantly improve the time trial performance of cyclists, while a low dose (1-3 mg/kg) does not yield improvement. In addition, the improvements in completion time and mean power output resulting from a moderate dose of caffeine are essentially the same in cycling time trails.

Effect of Long-term Oral Administration of Different Dosages of Caffeine on Anesthetic Emerging Time

This paper aims to investigate the effect of prolonged oral ingestion of different doses of caffeine on anesthetic emergence time. In our experiment, eighteen male mice were selected and randomly divided into three groups of six mice, each according to the concentration of caffeine administered: a high-concentration caffeine group, a low-concentration caffeine group, and a blank control group. Mice were anesthetized with isoflurane and Zoletil 50, and the time of emergence was recorded for both anesthesia and the time of entry into anesthesia was recorded for Zoletil 50 anesthesia. Twenty-four hours after the anesthesia experiments, the mice were subjected to Morris water maze experiments, visual station experiments, hidden station experiments, and spatial exploration experiments. The results showed that both high-dose and low-dose coffee ig accelerated isoflurane and Zoletil 50 anesthesia emerging, with the high-dose being statistically more significant for the acceleration of anesthesia emerging. Prolonged oral coffee administration did not affect the time to enter anesthesia. Long-term oral coffee administration enhanced spatial exploration and spatial learning memory after anesthesia.

A cost-effectiveness analysis for high versus standard (low) dose caffeine for the treatment of apnea in neonatal intensive care unit

A cost-effectiveness analysis for high versus standard (low) dose caffeine for the treatment of apnea in neonatal intensive care unit

Timing Matters: Time of Day Impacts the Ergogenic Effects of Caffeine—A Narrative Review

Caffeine has attracted significant attention from researchers in the sports field due to its well-documented ergogenic effects across various athletic disciplines. As research on caffeine continues to progress, there has been a growing emphasis on evaluating caffeine dosage and administration methods. However, investigations into the optimal timing of caffeine intake remain limited. Therefore, this narrative review aimed to assess the ergogenic effects of caffeine administration at different times during the morning (06:00 to 10:00) and evening (16:00 to 21:00). The review findings suggest that circadian rhythms play a substantial role in influencing sports performance, potentially contributing to a decline in morning performance. Caffeine administration has demonstrated effectiveness in mitigating this phenomenon, resulting in ergogenic effects and performance enhancement, even comparable to nighttime levels. While the specific mechanisms by which caffeine regulates circadian rhythms and influences sports performance remain unclear, this review also explores the mechanisms underlying caffeine’s ergogenic effects, including the adenosine receptor blockade, increased muscle calcium release, and modulation of catecholamines. Additionally, the narrative review underscores caffeine’s indirect impact on circadian rhythms by enhancing responsiveness to light-induced phase shifts. Although the precise mechanisms through which caffeine improves morning performance declines via circadian rhythm regulation necessitate further investigations, it is noteworthy that the timing of caffeine administration significantly affects its ergogenic effects during exercise. This emphasizes the importance of considering caffeine intake timing in future research endeavors to optimize its ergogenic potential and elucidate its mechanisms.

Synergetic effects of a low caffeine dose and pre-exercise music on psychophysical performance in female taekwondo athletes

Synergetic effects of a low caffeine dose and pre-exercise music on psychophysical performance in female taekwondo athletes

The association of caffeine and nandrolone decanoate modulates aversive memory and nociception in rats

Caffeine and anabolic–androgenic steroids (AAS) are commonly used to improve muscle mass and athletic performance. Nandrolone Decanoate (ND) is one of the most abused AAS worldwide, leading to behavioral changes in both humans and rodents. Caffeine, the most widely consumed psychostimulant globally, is present in various thermogenic and gym supplements. Low and moderate doses of caffeine antagonize adenosine receptors and have been linked to improved memory and pain relief. We have previously demonstrated that consuming caffeine prevents the risk-taking behavior triggered by nandrolone. In this study, we aimed to investigate the long-term effects of ND and caffeine, either alone or in combination, on passive avoidance memory and nociception. We used the step-down and hot-plate tasks in male and female Lister Hooded rats. Our results confirmed the antinociceptive effect of caffeine and indicated that chronic administration of the ND-caffeine association promotes the evocation of aversive memory in female rats.

Dose-Response Study of Caffeine on Postnatal Weight Gain in Premature Neonates-A Retrospective Cohort Study.

Caffeine citrate (CC)-induced excessive energy expenditure, diuresis, natriuresis, and other CC-associated potential side effects (CC-APSEs) result in lower daily weight gain (WG) in premature neonates. This study aimed to assess higher CC-doses' effect on the mean daily-WG (MD-WG) and CC-APSE development, considering 5mg/kg/day as the standard regimen. This retrospective cohort study included neonates of ≤36weeks gestational age and received CC-therapy. The same participants were followed for data analysis in two postnatal phases: 15-28 and 29-42days of life (DOL). Based on daily CC-dose, formed group-I=(5mg/kg/day), group-II=(>5-7mg/kg/day), and group-III=(>7mg/kg/day). Data was analyzed separately for group-II and group-III using group-I as the standard. The study included 284 neonates. During phase-I, the MD-WG was significantly higher in group-I than group-II (19.9 ± .88g/kg/d vs 17.5 ± .49, P = .031) and group-III (19.9 ± .88g/kg/d vs 16.7 ± .71, P < .001). During 29-42 DOL, the MD-WG of group-I was only significantly higher than group-III (21.5 ± .42g/kg/d vs 18.1 ± .39g/kg/d, P = .003) and comparable with group-II. During 15-28 DOL, CC-APSEs were significantly higher in group-II and group-III but during 29-42 DOL was significant only in group-III. Exposure to higher caffeine doses in this study cohort is associated with lower postnatal WG in preterm neonates than standard daily doses may be due to its catabolic effects and CC-APSEs.

Daily Caffeine Consumption May Increase the Risk of Acute Kidney Injury Related to Platinum-Salt Chemotherapy in Thoracic Cancer Patients: A Translational Study.

Although their efficacy has been well-established in Oncology, the use of platinum salts remains limited due to the occurrence of acute kidney injury (AKI). Caffeine has been suggested as a potential pathophysiological actor of platinum-salt-induced AKI, through its hemodynamic effects. This work aims to study the association between caffeine consumption and the risk of platinum-salt-induced AKI, based on both clinical and experimental data. The clinical study involved a single-center prospective cohort study including all consecutive thoracic cancer patients receiving a first-line platinum-salt (cisplatin or carboplatin) chemotherapy between January 2017 and December 2018. The association between daily caffeine consumption (assessed by a validated auto-questionnaire) and the risk of platinum-salt induced AKI or death was estimated by cause-specific Cox proportional hazards models adjusted for several known confounders. Cellular viability, relative renal NGAL expression and/or BUN levels were assessed in models of renal tubular cells and mice co-exposed to cisplatin and increasing doses of caffeine. Overall, 108 patients were included (mean age 61.7 years, 65% men, 80% tobacco users), among whom 34 (31.5%) experienced a platinum-salt-induced AKI (67% Grade 1) over a 6-month median follow-up. The group of high-caffeine consumption (≥386 mg/day) had a two-fold higher hazard of AKI (adjusted HR [95% CI], 2.19 [1.05; 4.57]), without any significant association with mortality. These results are consistent with experimental data confirming enhanced cisplatin-related nephrotoxicity in the presence of increasing doses of caffeine, in both in vitro and in vivo models. Overall, this study suggests a potentially deleterious effect of high doses of daily caffeine consumption on the risk of platinum-salt-related AKI, in both clinical and experimental settings.

Effects of Various Caffeine Doses on Cognitive Abilities in Female Athletes with Low Caffeine Consumption.

Caffeine (CAF), a prevalent psychoactive stimulant, is believed to potentially enhance cognitive ability. However, studies on the effects of various doses are limited and yield inconsistent results, particularly in female athletes. Therefore, we aimed to assess the association between three different dosages of CAF intake (low, moderate, and high) and cognitive skills in female athletes with low CAF consumption. This study had a randomized, crossover, double-blind design in which each athlete performed four experimental sessions after ingesting either a placebo (PLAC), 3 mg·kg-1 of CAF (3 mg of CAF), 6 mg·kg-1 of CAF (6 mg of CAF), or 9 mg·kg-1 of CAF (9 mg of CAF) with an in-between washout period of at least 72 h. Following a 60 min window post-capsule consumption, fourteen female athletes (age: 17.4 ± 0.8 years) were assessed through various cognitive tests, namely, simple reaction time (SRT), choice reaction time (CRT), and attentional task (AT) tests, along with the mental rotation test (MRT). Additionally, they were required to complete a questionnaire about the undesirable side effects of CAF. Our results indicated that, compared to those of PLAC, the SRT, CRT, and AT performance were significantly improved following the administration of both 3 mg of CAF and 6 mg of CAF. While the greatest enhancement was observed after consuming 3 mg of CAF, no significant differences were found between the effects of 3 mg and 6 mg of CAF. Interestingly, MRT performance did not improve with any of the CAF dosages. Moreover, the ingestion of 9 mg of CAF did not enhance cognitive skills and was linked to the highest occurrence of CAF-related side effects. In conclusion, our results highlight the recommendation for a low CAF dosage of 3 mg·kg-1, in contrast to a higher dose of 6 mg·kg-1 or 9 mg·kg-1 of CAF, to enhance various aspects of cognitive performance in female athletes with low CAF consumption without adverse side effects.

Combined effects of Rhodiola rosea and caffeine supplementation on aerobic endurance and muscle explosiveness: a synergistic approach.

This study examined the synergistic effects of combining Rhodiola rosea (RHO) and caffeine (CAF) supplementation on muscle endurance and explosiveness in SD rats and human subjects, encompassing individuals without prior exercise training experience and seasoned aerobic athletes. Male SD rats and healthy human volunteers were randomly divided into four groups: CAF, RHO, CAF + RHO, and a control group (CTR). Nutritional supplements were administered throughout the training period, and pre-and post-measurement data were collected. In both the rat model and human subjects, the RHO+CAF group demonstrated significantly greater effects compared to the use of RHO or CAF supplements individually. Rats in the RHO+CAF group demonstrated extended running and swimming times and an increase in erythropoietin (EPO) mRNA expression in comparison to the CTR. Blood parameters, such as serum EPO levels, were enhanced in the CAF + RHO group, while blood urea nitrogen (BUN) and lactate (LA) levels significantly decreased in both the RHO and CAF + RHO groups. Hepatic and muscle glycogen contents were also higher in these groups. The gene expression analysis in rats demonstrated an elevation in the mRNA levels of glucose transporter-4 (GLUT-4), peroxisome proliferator-activated receptor γ coactivator-1 alpha (PGC-1α), Monocarboxylate transporter 1 (MCT-1), and Heme Oxygenase-1 (HO-1) in both the RHO and RHO+CAF groups. For individuals without prior aerobic training experience, the RHO+CAF group showed significant improvements compared to the CTR group in maximal oxygen consumption (VO2max), 5 km run, countermovement jump (CMJ), standing long jump, and 30 m sprint. For individuals with years of aerobic training experience, the RHO+CAF group exhibited enhanced performance in the 5 km run, CMJ, and standing long jump compared to the CTR group. In conclusion, the continuous 30 days supplementation of RHO, combined with a single dose of CAF, demonstrated superior effects on muscle endurance and explosiveness in both animal and human studies when compared to the use of RHO or CAF individually.

Effect of Coffee and Chocolate Ingestion on Clozapine Dose and on Plasma Clozapine and Norclozapine Concentrations in Clinical Practice.

Some reports point to dietary caffeine intake as a cause of increased plasma clozapine concentrations in certain patients. We compared clozapine dose and plasma clozapine and N-desmethylclozapine (norclozapine) concentrations in male and female smokers and nonsmokers in relation to reported (i) coffee (caffeine) and (ii) chocolate (caffeine and theobromine) intake in samples submitted for clozapine therapeutic drug monitoring, 1993-2017. There was information on coffee ingestion for 16,558 samples (8833 patients) from males and 5886 samples (3433 patients) from females and on chocolate ingestion for 12,616 samples (7568 patients) from males and 4677 samples (2939 patients) from females. When smoking was considered, there was no discernible effect of either coffee or chocolate ingestion either on the median dose of clozapine or on the median plasma clozapine and norclozapine concentrations in men and in women. However, cigarette smoking was associated with higher coffee and chocolate consumption. Although male nonsmokers who reported drinking 3 or more cups of coffee daily had significantly higher median plasma clozapine and norclozapine concentrations than those who drank less coffee, they were also prescribed a significantly higher clozapine dose. There was no clear effect of coffee ingestion on plasma clozapine and norclozapine in female nonsmokers. Inhibition of clozapine metabolism by caffeine at the doses of caffeine normally encountered in those treated with clozapine is unlikely even in male nonsmokers. Measurement of plasma caffeine in an appropriate sample should be considered in any future investigation into a presumed clozapine-caffeine interaction.

Caffeine pharmacokinetics following umbilical vein injection during delayed cord clamping in preterm lambs.

Spontaneous breathing during and after delayed cord clamping (DCC) stabilizes cardiopulmonary transition at birth. Caffeine stimulates breathing and decreases apnea in premature newborns. We evaluated the pharmacokinetics and physiological effects of early caffeine administration-direct injection into the umbilical vein (UV) during DCC or administered through a UV catheter (UVC) after delivery. Eighteen extremely premature lambs (125-127d, term gestation 145d) were exteriorized and instrumented. Lambs received caffeine-citrate at high (40 mg/kg) or standard-dose (20 mg/kg) via direct UV (DUV) injection during DCC, or via the UVC. Mean peak plasma caffeine concentrations were lower with high-dose DUV compared to UVC (18 ± 4.3 vs. 46 ± 12 mg/L, p < 0.05). With standard-dose caffeine, mean peak plasma levels were 7.48 ± 2.6 with DUV and 28.73 ± 9.4 mg/L with UVC. The volume of distribution was higher in the DUV group compared to UVC (2.5 ± 1.0 vs. 0.69 ± 0.15 L/kg) with an estimated 39 ± 18% entering the maternal circulation. Maternal peak concentrations were 0.79 ± 0.71 and 1.43 ± 0.74 mg/L with standard and high-dose DUV, respectively. Caffeine injected directly into the UV during DCC is feasible but achieves lower concentrations due to high volume of distribution including maternal circulation. Further trials evaluating DUV caffeine injection should use higher caffeine doses. Respiratory stimulation with early caffeine may reduce the need for intubation in preterm infants. In the preterm lambs, caffeine injection directly into the umbilical vein during delayed cord clamping is feasible. Plasma caffeine concentrations are less than half when administered directly into the umbilical vein during delayed cord clamping compared to administration via an umbilical venous catheter following birth likely attributed to a larger volume of distribution or injection site leak. There were no significant hemodynamic alterations following caffeine injection.

Caffeine gum improves 5 km running performance in recreational runners completing parkrun events

PurposeThe purpose of this study was to determine whether caffeine gum improves the performance of recreational runners completing parkruns (weekly, 5 km, mass participant running events).MethodsThirty-six recreational runners (M = 31, F = 5; age 33.7 ± 10.7 y; BMI 23.1 ± 2.4 kg/m2) capable of running 5 km in < 25 min were recruited to a study at the Sheffield Hallam parkrun, UK. Runners were block randomized into one of three double-blind, placebo-controlled, cross-over intervention trials with caffeine gum as the treatment (n = 6 per intervention trial) or into one of three non-intervention trials that ran concurrently with the intervention trials (n = 6 per non-intervention trial). Changes in conditions across different parkruns were adjusted for using data from the non-intervention trials. Runners in the randomized cross-over intervention trials chewed gum supplying 300 mg of caffeine or a placebo gum for 5 min, starting 30 min before each parkrun.ResultsCaffeine gum improved 5 km parkrun performance by a mean of 17.28 s (95% CI 4.19, 30.37; P = 0.01). Adjustment for environmental conditions using data from the non-intervention trials attenuated the statistical significance (P = 0.04). Caffeine gum also decreased RPE by 1.21 (95% CI 0.30, 2.13; P = 0·01) units relative to placebo.ConclusionsA 300 mg dose of caffeine supplied in chewing gum improved the performance of recreational runners completing 5 km parkruns by an average of 17 s.Trial RegistrationThe study was registered at ClinicalTrials.gov: NCT02473575 before recruitment commenced.