Caffeine Abstinence Research Articles

Submaximal adenosine‐induced coronary hyperaemia with 12 h caffeine abstinence: implications for clinical adenosine perfusion imaging tests

Adenosine is widely used as a vasodilator agent in myocardial perfusion imaging. Caffeine inhibits the effect, but the time of caffeine abstinence needed is under discussion and varies from 12 to 24h. Therefore, our aim was to examine whether the time of caffeine abstinence affects the hyperaemic response using quantification of coronary sinus flow (CS F) with cardiac magnetic resonance (CMR) during adenosine infusion. Healthy individuals (n=16, eight females, age 41±3years) underwent two CMR examinations with 12 and 24h of caffeine abstinence. CS F was quantified with phase-contrast velocity mapping (PC-)CMR during adenosine infusion (140μgkg(-1) min(-1) ) and rest and the CS F reserve between adenosine and rest was calculated. Myocardial perfusion (MP) was calculated as CS F×heart rate/left ventricular mass. Cardiac output (CO) was quantified using PC-CMR of the ascending aorta. The CS F reserve was lower after 12h abstinence compared to 24h (4·31±0·57 versus 5·32±0·76, P=0·03). In six of 16 subjects (38%), CS F reserve was >30% higher with longer caffeine abstinence. MP during adenosine was lower after 12h compared to 24h caffeine abstinence (3·59±0·37 versus 4·23±0·28 mlmin(-1) g(-1) ; P=0·046). The increase in CO during adenosine between the two occasions did not differ (55±7% and 55±6%, P=0·11). Interobserver variability for CS F/heartbeat was -0·05±1·00ml. Hyperaemia during adenosine is lower in some patients with 12h of caffeine abstinence compared to 24h. Longer caffeine abstinence, that is 24h, is of value before pharmacological stress testing as the individual response is not known and the individual variation is large.

Caffeine withdrawal: Cost or benefit?

Caffeine ingestion has been shown to enhance alertness and performance. However, caffeine ingestion before bed has also been shown to lower the quality and quantity of sleep. For several reasons, including improved sleep hygiene to prevent or treat insomnia, caffeine withdrawal may be suggested. Many studies have shown negative effects during the first few days of caffeine withdrawal including headaches, lethargy, and irritability. Very few studies have continued observations beyond these immediate negative effects to determine the longer term effects. In other words, are individuals benefited or impaired given a longer period free of caffeine compared to the normal caffeine consumption period? The present study investigated a period of several weeks following caffeine withdrawal. Participants were 23 healthy young adult caffeine consumers. In addition to a caffeine consumption diary they recorded subjective evaluations of their day at 6 pm each day on a web based survey. The evaluations included headache symptoms, alertness, fatigue, moods, sleep, and overall quality of daily functioning. Measures were collected daily for a baseline week of normal caffeine consumption, a week of gradual withdrawal, and four additional weeks of caffeine abstention. Repeated measures statistical analyses compared means for the baseline week, withdrawal week and the fourth week free of caffeine. During the week of withdrawal reported headaches and sleep length increased while alertness and overall day quality decreased compared to baseline caffeine consumption. However, by the last week all of these measures had returned to be comparable with the baseline week and in most cases were marginally but not significantly better than baseline week. From this initial pilot study of the longer term subjective effects of caffeine withdrawal it appears that individuals rate their moods, sleep, and daytime functioning at least as favorably as during the baseline period of their normal caffeine consumption. Further studies including randomized placebo control trials using objective measures of sleep and performance are required to confirm these initial pilot findings. Kristen Johannson who carried out this study as part of her Psychology Honours degree.

Caffeine: Public Concern and the Precautionary Principle

Caffeine: Public Concern and the Precautionary Principle

The effects of caffeine abstinence on sleep: A pilot study

AimThe aim of this study was to examine whether caffeine abstinence in the evening could improve the sleep quality of those who habitually consume coffee. DesignA double-blind control group design (caffeine and caffeine-free groups). SettingA university. SubjectsA convenience sampling of 10 students (mean age 21.4years). MethodsIt was a 14-day experiment. For the first 7days, all participants consumed caffeinated coffee. In the following 7days, subjects consumed caffeinated or decaffeinated coffee according to their assigned group. MeasuresSleep–wake parameters, self-reported sleep quality and level of refreshment. ResultsThere were no significant differences (p>.05) among the data of the two groups identified. No significant changes (p>.05) were found in the sleep quality of either group during the study. ConclusionThis study confirms that caffeine abstinence in the evening might not be helpful in sleep promotion. It highlights the need to implement evidence-based practice in health promotion.

Effect of an Energy Drink on Physical and Cognitive Performance in Trained Cyclists

Background: Caffeine and carbohydrates are used by consumers to increase exercise and certain aspects of cognitive performance. This study investigated the effectiveness of an energy drink (ED) containing caffeine to enhance cycling time-trial performance and cognitive performance at rest, during strenuous exercise, and after exercise. Methods: The experimental protocol was a double-blind, placebo-controlled, randomized, crossover design. The treatments were ED containing caffeine (160 mg), carbohydrate (54 g), taurine, and Panax ginseng, and a caffeine-free noncaloric placebo beverage (PLA). After a 12-hour calorie and caffeine abstention, exercise performance was measured by time to finish a simulated 35-km cycling time-trial course. Cognitive performance was measured by a Stroop Test, a tapping task, a reaction time task, and an executive function task consisting of both tapping and reaction time. Participants (n=15, seven women, eight men) were grouped as low-baseline (LO) or high-baseline (HI) since 5 of 15 participants (3 women, 2 men) had elevated baseline blood caffeine concentrations at both experimental trials. Results: Race performance improved by an average of 3% in both LO and HI groups when participants consumed ED compared with PLA. Although VO2 and heart rate were greater throughout the race for ED compared with PLA, there was no difference in perceived exertion between treatments. ED also increased taps per second in the tapping task before and after exercise. Conclusions: The results suggest that ED is an effective pre-exercise supplement that can improve cycling time-trial performance and possibly simple aspects of cognitive function even under elevated basal blood caffeine levels.

The effects of a caffeine-containing beverage on neuromuscular performance during a multi-joint, lower body power exercise

Background Current research has shown varied results when comparing the effects of caffeinated beverages on explosive exercise movements. We hypothesized that lower body muscular explosiveness would be significantly increased (p < 0.05) after Redline ® energy drink ingestion versus a similar placebo (PLB) drink in recreationally active subjects (n=16). Methods After a day of dietary control and caffeine abstinence, otherwise-fasted participants performed four separate, strict squat jumps (SJ) under both conditions 48 – 96 hours apart. The variables measured included peak power (POW), peak force (FOR), peak velocity (VEL), maximal displacement (DSP), and maximal rate of force development (RFD) in the SJ for both Redline ® energy drink and

Effect of Caffeine on Plasma Glucose and Insulin Response to Mixed Meal Tolerance Test in Type II Diabetes

Caffeine containing beverages is widely used and popular world-wide. Studies showed that caffeine acutely decreased insulin sensitivity in young, non-diabetic adults.3-5 This double-blind study was carried out with habitual coffee drinkers who had at least a 6-months history of type II diabetes. The effects of caffeine on fasting glucose &amp; insulin levels and on glucose &amp; insulin response to a mixed-meal tolerance test were studied. The total daily caffeine intake was 375 mg in a divided schedule. Overnight fast and caffeine abstinence baseline fasting blood samples were drawn then after administration of caffeine (250 mg/day) or placebo they consumed a commercial meal that contained 75 gram of carbohydrate for mixed-meal tolerance test. Comparisons of the AUC2h values demonstrated significant caffeine effects for both plasma glucose and plasma insulin (P &lt; 0.05) responses to the mixed-meal tolerance test. Caffeine did not affect the fasting levels of plasma glucose or insulin when compared with placebo. It may be concluded that acute administration of caffeine plus carbohydrate impaired post-prandial glucose metabolism and insulin responses. Such effects could have implication for the management of type II diabetic patients. Medicine Today 2010 Volume 22 Number 02 Page 73-74 DOI: http://dx.doi.org/10.3329/medtoday.v22i2.12437

Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance

Despite 100years of psychopharmacological research, the extent to which caffeine consumption benefits human functioning remains unclear. To measure the effects of overnight caffeine abstinence and caffeine administration as a function of level of habitual caffeine consumption. Medium-high (n = 212) and non-low (n = 157) caffeine consumers completed self-report measures and computer-based tasks before (starting at 10:30AM) and after double-blind treatment with either caffeine (100mg, then 150mg) or placebo. The first treatment was given at 11:15AM and the second at 12:45PM, with post-treatment measures repeated twice between 1:45PM and 3:30PM. Caffeine withdrawal was associated with some detrimental effects at 10:30AM, and more severe effects, including greater sleepiness, lower mental alertness, and poorer performance on simple reaction time, choice reaction time and recognition memory tasks, later in the afternoon. Caffeine improved these measures in medium-high consumers but, apart from decreasing sleepiness, had little effect on them in non-low consumers. The failure of caffeine to increase mental alertness and improve mental performance in non-low consumers was related to a substantial caffeine-induced increase in anxiety/jitteriness that offset the benefit of decreased sleepiness. Caffeine enhanced physical performance (faster tapping speed and faster simple and choice reaction times) in both medium-high and non-low consumers. While caffeine benefits motor performance and tolerance develops to its tendency to increase anxiety/jitteriness, tolerance to its effects on sleepiness means that frequent consumption fails to enhance mental alertness and mental performance.

The effects of caffeinated and decaffeinated coffee on sex hormone-binding globulin and endogenous sex hormone levels: a randomized controlled trial

BackgroundFindings from observational studies suggest that sex hormone-binding globulin (SHBG) and endogenous sex hormones may be mediators of the putative relation between coffee consumption and lower risk of type 2 diabetes. The objective of this study was to evaluate the effects of caffeinated and decaffeinated coffee on SHBG and sex hormone levels.FindingsAfter a two-week run-in phase with caffeine abstention, we conducted an 8-week parallel-arm randomized controlled trial. Healthy adults (n = 42) were recruited from the Boston community who were regular coffee consumers, nonsmokers, and overweight. Participants were randomized to five 6-ounce cups of caffeinated or decaffeinated instant coffee or water (control group) per day consumed with each meal, mid-morning, and mid-afternoon. The main outcome measures were SHBG and sex hormones [i.e., testosterone, estradiol, dehydroepiandrosterone sulfate].No significant differences were found between treatment groups for any of the studied outcomes at week 8. At 4 weeks, decaffeinated coffee was associated with a borderline significant increase in SHBG in women, but not in men. At week 4, we also observed several differences in hormone concentrations between the treatment groups. Among men, consumption of caffeinated coffee increased total testosterone and decreased total and free estradiol. Among women, decaffeinated coffee decreased total and free testosterone and caffeinated coffee decreased total testosterone.ConclusionsOur data do not indicate a consistent effect of caffeinated coffee consumption on SHBG in men or women, however results should be interpreted with caution given the small sample size. This is the first randomized trial investigating the effects of caffeinated and decaffeinated coffee on SHBG and sex hormones and our findings necessitate further examination in a larger intervention trial.

Caffeine Occupancy of Human Cerebral A1 Adenosine Receptors: In Vivo Quantification with 18F-CPFPX and PET

Caffeine is the neuroactive agent in coffee and tea and is a broadly consumed stimulant. It is a nonselective antagonist of the neuromodulator adenosine and, if applied in commonly consumed doses, evokes its stimulating effects through the blockade of adenosine receptors. (18)F-8-cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine ((18)F-CPFPX) has been established as a highly selective and affine PET ligand for the A(1) adenosine receptor (A(1)AR). The objective of the present study was to visualize and quantify the in vivo occupancy of the human cerebral A(1)AR by caffeine using (18)F-CPFPX and PET. Fifteen subjects (age range, 24-68 y) underwent a 140-min bolus-plus-constant-infusion PET experiment after at least 36 h of caffeine abstinence. Metabolite-corrected blood data were used to calculate steady-state distribution volumes (V(T)) during the baseline condition of the scan between 70 and 90 min. Subsequently, subjects received a 10-min infusion of varying concentrations (0.5-4.3 mg/kg of body weight) of caffeine at 90 min. Occupancy V(T) of the A(1)AR was thereafter estimated using data acquired between 120 and 140 min. Occupancy levels were calculated using the Lassen plot, from which the inhibitory concentrations of 50% were derived. Plasma levels of caffeine were determined at regular intervals. One subject received an intravenous vehicle as a placebo. Caffeine displaced 5%-44% of (18)F-CPFPX binding in a concentration-dependent manner. There was no change of radioligand binding after the administration of placebo. Half-maximal displacement was achieved at a plasma caffeine concentration of 67 μM, which corresponds to 450 mg in a 70-kg subject or approximately 4.5 cups of coffee. Given a biologic half-life of about 5 h, caffeine might therefore occupy up to 50% of the cerebral A(1)AR when caffeinated beverages are repeatedly consumed during a day. Furthermore, the present study provides evidence that (18)F-CPFPX PET is suitable for studying the cerebral actions of caffeine, the most popular neurostimulant worldwide.

Pilot Study of Caffeine Abstinence for Control of Chronic Glucose in Type 2 Diabetes

BACKGROUND: A growing body of evidence suggests that caffeinated beverages may impair chronic glucose control in type 2 diabetes. This pilot study tested the chronic effects of caffeine abstinence on glucose control in type 2 diabetic patients who were daily coffee drinkers. METHODS: Twelve coffee drinkers (six males) with established type 2 diabetes participated. Seven (five males) completed 3 months of total caffeine abstinence. Measures of chronic glucose control, long-term (hemoglobin A1c [HbA1c]) and short-term (1,5-anhydroglucitol [1,5-AG]), were collected at baseline and during follow-up. Abstinence was established by diaries confirmed by saliva caffeine assays. RESULTS: Abstinence produced significant decreases in HbA1c and increases in 1,5-AG, both indicating improvements in chronic glucose control. Fasting glucose and insulin did not change, nor were changes in body weight observed. CONCLUSIONS: Although preliminary, these results suggest that caffeine abstinence may be beneficial for patients with type 2 diabetes. This hypothesis should be confirmed in larger controlled clinical trials.

Development of the Caffeine Withdrawal Symptom Questionnaire: Caffeine withdrawal symptoms cluster into 7 factors

BackgroundHabitual caffeine consumers who abstain from caffeine experience withdrawal symptoms such as headache, fatigue, difficulty concentrating, mood disturbances, and flu-like symptoms (Juliano and Griffiths, 2004). The caffeine withdrawal syndrome has been documented across many experimental studies; however, little is known about how withdrawal symptoms co-vary during a discrete episode. Furthermore, a validated measure of caffeine withdrawal is lacking. ObjectiveTo develop, evaluate, and reduce a 23-item measure of caffeine withdrawal symptoms; the Caffeine Withdrawal Symptom Questionnaire (CWSQ), to a set of composite variables. MethodsCaffeine consumers (N=213) completed the CWSQ after 16h of caffeine abstinence. A subset of participants also completed the CWSQ during a preceding baseline period and/or after double-blind consumption of caffeinated coffee. ResultsPrincipal components analysis resulted in a solution comprised of 7-factors: 1. Fatigue/drowsiness; 2. Low alertness/difficulty concentrating; 3. Mood disturbances; 4. Low sociability/motivation to work; 5. Nausea/upset stomach; 6. Flu-like feelings; and 7. Headache. With the exception of nausea/upset stomach, the CWSQ total score and individual composite scores were significantly greater during caffeine abstinence relative to both baseline and double-blind consumption of caffeinated coffee, thereby demonstrating sensitivity of the measure. Compared to non-daily coffee consumers, daily consumers had greater increases in total withdrawal, fatigue/drowsiness, low alertness/difficulty concentrating, mood disturbances, and headache. ConclusionsFuture directions include replication, assessment on a clinical population, and further examination of psychometric properties of the CWSQ. The CWSQ should facilitate the assessment and diagnosis of caffeine withdrawal and increase our knowledge of the caffeine withdrawal syndrome.

Pharmacokinetics of caffeine in plasma and saliva, and the influence of caffeine abstinence on CYP1A2 metrics

To investigate the utility of metrics of CYP1A2 activity using caffeine as a probe, and saliva and plasma sampling with or without a 24-h caffeine abstinence. This was a cross-over pharmacokinetic study in 30 healthy male subjects who received a single oral 100mg caffeine dose after 24-h caffeine abstinence or after maintaining their regular caffeine intake (no caffeine abstinence). Serial blood and saliva samples were collected simultaneously over 24h. Caffeine and paraxanthine concentrations were measured using a validated HPLC assay. There was a strong correlation between the paraxanthine/caffeine AUC(0-24) ratio (reference metric) and the paraxanthine/caffeine concentration (C(t) ) ratio at 4h (C(4) ) in both saliva and plasma (r≥0.75). The paraxanthine/caffeine AUC(0-24) ratio in plasma and saliva did not differ between the 24-h caffeine abstinence and the no abstinence period (P>0.05). The optimal paraxanthine/caffeine C(t) that correlated with the plasma paraxanthine/caffeine AUC(0-24) ratio in the 24-h abstinence period was 2 and 4h (r=0.88) in plasma, and 4 and 6h in saliva (r=0.70), while it was the saliva 4h time-point in the no abstinence period (r=0.78). The saliva paraxanthine/caffeine concentration ratio at 4h was a suitable metric to assess CYP1A2 activity after oral administration of caffeine without the need for 24-h caffeine abstinence.

Caffeine Supplementation Had No Effect on Endurance Capacity in Elderly Subjects Who Had Abstained from Caffeine-Containing Nutrition for 8 Hours

Background: In this study, we investigated the effect of acute caffeine ingestion on physical performance after only 8 hours of caffeine abstinence. Methods: The study was a randomized, double-blind, cross-over study and included 30 healthy subject aged ≥70 years who had been recruited by their general practitioner. The participants abstained from caffeine for 8 hours (overnight) and the next morning they received placebo and then caffeine (6 mg/kg), or caffeine and then placebo at an interval of 1 week. One hour after the intervention we measured cycling endurance (ergometer), perceived effort during cycling (Borg scale), postural stability (force platform), and maximal isometric arm flexion strength and endurance (dynamometer chair). Blood samples were taken before the intervention, before cycling, after 5 minutes of cycling, and at exhaustion. Results: The participants had a usual coffee intake of six cups/day and after 8 hours of caffeine abstinence the plasma concentration of caffeine was 4.1 μM. Caf...

Caffeine And Sprinting Performance: Dose Responses And Efficacy

PURPOSE: The aims of this study were to evaluate the effects of caffeine supplementation on short-duration sprint cycling performance and to determine if there was a dose-response effect. METHODS: Using a randomised, double-blind, placebo-controlled design, 17 well-trained males (means ± standard deviation for age, height, body mass, and body fat of the subjects were: 24 ± 6 years, 1.82 ± 0.06 m, 82.2 ± 6.9 kg, and 13.5 ± 3.4%, respectively) completed seven maximal 10 s sprint trials on an electromagnetically-braked cycle ergometer, with a minimum of 48 hours between trials. Apart from Trial 1, which was used for familiarisation purposes, all trials required subjects to ingest a gelatine capsule containing either caffeine or placebo (maltodextrin) one hour prior to performing each sprint. To examine dose-response effects, the following doses of caffeine were used: 2, 4, 6, 8, and 10 mg·kg-1. RESULTS: The absence of significant differences in baseline measures of plasma caffeine concentration (established via high performance liquid chromatography) (grand mean: 0.14 ± 0.28 μg·ml-1; p = 0.30) confirmed subject compliance with caffeine abstinence prior to each trial. There was, as anticipated, a significant supplement × time interaction (p < 0.001) with larger caffeine doses producing higher post-supplementation plasma caffeine levels. In comparison with placebo, the results revealed no significant effect of supplementation on peak power (grand mean: 1135 ± 192 W; p = 0.11), mean power (grand mean: 774 ± 111 W; p = 0.55), or time to peak power (grand mean: 4.45 ± 1.16 s; p = 0.17). CONCLUSION: In contrast with the established benefits of caffeine supplementation on endurance performance, the results of this study show that caffeine supplementation has no effect on short-duration sprint cycling performance, irrespective of the dosage used.

Caffeine, Glucose Metabolism, and Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a serious public health problem. A growing body of evidence suggests that consumption of caffeine leads to disruptions of glucose metabolism that could be of concern for both the development of T2DM and its clinical management. At least 17 studies have consistently demonstrated that caffeine administration in healthy, nondiabetic adults produces an acute increase in insulin resistance or impairment of glucose tolerance, an effect that could contribute to T2DM disease progression in susceptible individuals. Studies of coffee drinkers who have T2DM have found that caffeine exaggerates the rise in glucose after carbohydrate ingestion, an effect that could contribute to higher chronic glucose levels and impaired clinical control. The results of these well-controlled experimental studies contradict epidemiological studies that find that heavy coffee drinking is associated with a lower risk of T2DM. Although it is premature to recommend caffeine abstinence for patients with T2...

Habitual coffee and tea drinkers experienced increases in blood pressure after consuming low to moderate doses of caffeine; these increases were larger upright than in the supine posture

Caffeine users have been encouraged to consume caffeine regularly to maintain their caffeine tolerance and so avoid caffeine's acute pressor effects. In controlled conditions complete caffeine tolerance to intervention doses of 250 mg develops rapidly following several days of caffeine ingestion, nevertheless, complete tolerance is not evident for lower intervention doses. Similarly complete caffeine tolerance to 250 mg intervention doses has been demonstrated in habitual coffee and tea drinkers' but for lower intervention doses complete tolerance is not evident. This study investigated a group of habitual caffeine users following their self-determined consumption pattern involving two to six servings daily. Cardiovascular responses following the ingestion of low to moderate amounts caffeine (67, 133 and 200 mg) were compared with placebo in a double-blind, randomised design without caffeine abstinence. Pre-intervention and post-intervention (30 and 60 min) 90 s continuous cardiovascular recordings were obtained with the Finometer in both the supine and upright postures. Participants were 12 healthy habitual coffee and tea drinkers (10 female, mean age 36). Doses of 67 and 133 mg increased systolic pressure in both postures while in the upright posture diastolic pressure and aortic impedance increased while arterial compliance decreased. These vascular changes were larger upright than supine for 133 mg caffeine. Additionally 67 mg caffeine increased dp/dt and indexed peripheral resistance in the upright posture. For 200 mg caffeine there was complete caffeine tolerance. Cardiovascular responses to caffeine appear to be associated with the size of the intervention dose. Habitual tea and coffee drinking does not generate complete tolerance to caffeine as has been previously suggested. Both the type and the extent of caffeine induced cardiovascular changes were influenced by posture.

Association of the Anxiogenic and Alerting Effects of Caffeine with ADORA2A and ADORA1 Polymorphisms and Habitual Level of Caffeine Consumption

Caffeine, a widely consumed adenosine A(1) and A(2A) receptor antagonist, is valued as a psychostimulant, but it is also anxiogenic. An association between a variant within the ADORA2A gene (rs5751876) and caffeine-induced anxiety has been reported for individuals who habitually consume little caffeine. This study investigated whether this single nucleotide polymorphism (SNP) might also affect habitual caffeine intake, and whether habitual intake might moderate the anxiogenic effect of caffeine. Participants were 162 non-/low (NL) and 217 medium/high (MH) caffeine consumers. In a randomized, double-blind, parallel groups design they rated anxiety, alertness, and headache before and after 100 mg caffeine and again after another 150 mg caffeine given 90 min later, or after placebo on both occasions. Caffeine intake was prohibited for 16 h before the first dose of caffeine/placebo. Results showed greater susceptibility to caffeine-induced anxiety, but not lower habitual caffeine intake (indeed coffee intake was higher), in the rs5751876 TT genotype group, and a reduced anxiety response in MH vs NL participants irrespective of genotype. Apart from the almost completely linked ADORA2A SNP rs3761422, no other of eight ADORA2A and seven ADORA1 SNPs studied were found to be clearly associated with effects of caffeine on anxiety, alertness, or headache. Placebo administration in MH participants decreased alertness and increased headache. Caffeine did not increase alertness in NL participants. With frequent consumption, substantial tolerance develops to the anxiogenic effect of caffeine, even in genetically susceptible individuals, but no net benefit for alertness is gained, as caffeine abstinence reduces alertness and consumption merely returns it to baseline.

Dose Response of Caffeine on 2000-m Rowing Performance

To determine whether a dose-response relationship exists between caffeine and 2000-m rowing performance. In this randomized, placebo-controlled, double-blind crossover study, 10 competitive male rowers (mean +/- SD: age = 20.6 +/- 1.4 yr, body mass = 87.7 +/- 10.5 kg, height = 186.8 +/- 6.8 cm, (.)VO2peak = 5.1 +/- 0.6 L x min(-1)) consumed 2, 4, or 6 mg x kg(-1) caffeine or a placebo 60 min before completing a 2000-m time trial on a rowing ergometer. The trials were preceded by a 24-h standardized diet (including a light preexercise meal of 2 g x kg(-1) CHO), and subjects were tested preexercise for hydration, caffeine abstinence, and blood glucose concentrations. Time trial performance was not significantly different across the three caffeine doses or placebo (P = 0.249). After the three caffeine trials, postexercise plasma glucose and lactate concentrations were higher compared with the placebo trial (P < 0.05). Plasma caffeine concentrations after 60 min of ingestion were lower than the values reported previously by others following the same dose, and there was considerable interindividual variation in plasma caffeine concentrations in response to the various caffeine doses. The large interindividual response to the caffeine doses suggests that individual characteristics need to be considered when administering caffeine for performance enhancement. In addition, preexercise feeding may significantly affect plasma caffeine concentrations and the potential for caffeine to improve performance.

Effects of caffeine abstinence on adenosine induced coronary flow reserve quantified on phase contrast velocity encoded MRI of the coronary sinus

Introduction: Adenosine is a common pharmacological vasodilator agent used in first pass perfusion MRI as well as nuclear cardiology and echocardiography. Coronary flow reserve (CFR) by adenosine is inhibited by caffeine and therefore caffeine abstinence is routinely proscribed in patients. However, the guidelines differ regarding how long abstinence is needed from 12 to 24 hours. Purpose: This study was performed to investigate if 12 h caffeine abstinence is enough to provide maximal coronary flow reserve (CFR). Methods: 12 healthy individuals (5 females, 39 ± 14 years) were imaged using a 1.5 T Philips Intera CV at rest and during adenosine infusion (140 μg/kg/min) at two occasions, after 12 and 24 h caffeine abstinence respectively. Coronary sinus flow was measured during breath hold with a phase contrast velocity encoded (PC) TFE sequence with 20 phases per cardiac cycle. Typical imaging parameters were: SENSE factor 2, TE/TR/flip: 3.1/4.8 ms/15°, turbo factor 5, spatial resolution 1.2 × 1.2 × 7 mm and VENC 80 cm/s. CFR was calculated as the ratio between coronary sinus flow/min at adenosine and rest. Cardiac output was measured using PC-MRI of the ascending aorta. Results: CFR was higher (5.4 ± 1.0) at 24 h caffeine abstinence compared to 12 h (4.6 ± 0.8, p = 0.03). In most patients the difference was minimal but in three patients (25%) the increase in CFR at 12 h was less than 30% of that at 24 h caffeine abstinence. The increase in HR did not differ at 24 h (40 ± 7%) and 12 h abstinence (39 ± 5%, p = 0.62) nor did the increase in cardiac output (55 ± 8% vs. 48 ± 8%, p = 0.68). Reported symptoms and the blood pressure reaction did not differ between 24 h and 12 h abstinence, Figure 1. Conclusion: Twelve hours caffeine abstinence results in a lower coronary flow reserve compared to 24 hours and there is a large inter-individual difference to caffeine abstinence. This needs to be taken into consideration when performing adenosine perfusion imaging studies. (Figure Presented). (Less)