Jack E. James

Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation

RationaleAlthough it is widely believed that caffeine can enhance human performance and mood, the validity of this belief has been questioned, giving rise to debate. The central question is whether superior performance and mood after caffeine represent net benefits, or whether differences between caffeine and control conditions are due to reversal of adverse withdrawal effects.ObjectivesTo provide a focussed review of relevant experimental studies with the aim of clarifying current understanding regarding the effects of caffeine on human performance and mood.MethodsTo avoid the shortcomings of standard placebo-controlled studies, which are ambiguous due to failure to control for the confounding influence of withdrawal reversal, three main experimental approaches have been employed: studies that compare consumers and low/non-consumers, pre-treatment and ad lib consumption studies, and long-term withdrawal studies.ResultsOf the three approaches, only long-term withdrawal studies are capable of unambiguously revealing the net effects of caffeine. Overall, there is little evidence of caffeine having beneficial effects on performance or mood under conditions of long-term caffeine use vs abstinence. Although modest acute effects may occur following initial use, tolerance to these effects appears to develop in the context of habitual use of the drug.ConclusionsAppropriately controlled studies show that the effects of caffeine on performance and mood, widely perceived to be net beneficial psychostimulant effects, are almost wholly attributable to reversal of adverse withdrawal effects associated with short periods of abstinence from the drug.

A Meta-analysis of the effects of experimental manipulations of social support during laboratory stress

Abstract A meta-analysis was conducted on 22 experimental studies of the effects of social support on reactivity to laboratory stress. The analysis included 26 comparisons and 56 effect sizes, with the number of participants in each comparison ranging from 20 to 104. The average effect size was 0.61 for heart rate and systolic blood pressure, 0.5 1 for diastolic blood pressure, 0.25 for skin conductance, and 0.83 for cortisol. It was concluded that the laboratory analogues examined to date provide tentative confirmation of the hypothesis that social support has a protective health effect. Recommendations BIT made for future mearch, including the need to improve statistical power, expand subject participation beyond students; and increase consistency between studies in relation to measurements of social support effects, methods for manipulating social support, and types of behavioral challenges and control procedures used.

Acute and Chronic Effects of Caffeine on Performance, Mood, Headache, and Sleep

Despite being the most widely consumed psychoactive substance in the world, there is considerable confusion regarding the effects of caffeine. This study examined objective indices of performance, and self-reported mood, headache, and sleep in 36 healthy male and female habitual caffeine consumers exposed to a pattern of moderate intake. A double-blind placebo-controlled cross-over design with counterbalancing was employed in which all subjects participated in four experimental conditions involving the ingestion of placebo or caffeine 3 times daily for 6 days followed by a 7th (challenge) day of placebo or caffeine ingestion. No evidence was found that caffeine improved performance, either in the context of acute or habitual use. On the contrary, performance was found to be significantly impaired when caffeine was withdrawn abruptly following habitual use. Participants reported feeling more alert and less tired following acute ingestion of caffeine, but feeling less alert in conjunction with chronic exposure to the drug. In addition, caffeine withdrawal was associated with reported increasses in frequency and severity of headache, and with reports of sleeping longer and more soundly.

Adolescent substance use, sleep, and academic achievement: evidence of harm due to caffeine.

Using academic achievement as the key outcome variable, 7377 Icelandic adolescents were surveyed for cigarette smoking, alcohol use, daytime sleepiness, caffeine use, and potential confounders. Structural equation modeling (SEM) was used to examine direct and indirect effects of measured and latent variables in two models: the first with caffeine excluded and the second with caffeine included. A substantial proportion of variance in academic achievement, which might otherwise have been attributed to the harmful effects of cigarette smoking and alcohol use, was found to be attributable to caffeine. Evidence was obtained that daytime sleepiness, which was found to be independently associated with usage of licit substances (nicotine and alcohol) and caffeine, may be an important mediator of the negative impact of those substances on academic achievement. Findings suggest the importance of including measurements of caffeine consumption in future studies of adolescent substance use.

The Modification of Parent Behavior A Review of Generalization and Maintenance

This article reviews the literature on the extratraining effects of behavioral family intervention relating to parent behavior. The review classifies generalization and maintenance into several distinct categories suggested by Drabman, Hammer, and Rosenbaum (1979). The authors conclude that only limited aspects of generalization and maintenance questions in parent training have been addressed and highlight several persisting methodological deficiencies that have hampered the development and evaluation of effective generalization programming technologies.

Effects of video-relayed social support on hemodynamic reactivity and salivary cortisol during laboratory-based behavioral challenge.

The authors tested the effects of a laboratory analogue of social support on reactivity to laboratory-based behavioral challenge. Video-relayed supportive commentary was provided by a same-sex confederate while participants (40 healthy men and women assigned to support and no-support groups) performed a demanding computer task, and their heart rate, systolic and diastolic blood pressure, and salivary cortisol were measured. The authors found that heart rate and cortisol level (but not blood pressure) were attenuated in the support condition for both genders. Objective performance on the task was similar in both groups, but the social support group reported higher levels of perceived support and rated the task as easier than did participants in the no-support condition. Video presentation offers new opportunities for systematically examining social support and its effects.

Chronic Effects of Habitual Caffeine Consumption on Laboratory and Ambulatory Blood Pressure Levels

Background: Uncertainty continues to surround the role of habitual caffeine consumption as a cardiovascular risk factor. The present study examined the effects of moderate caffeine intake on 24 h blood pressure and heart rate in normotensive men and women. Methods: A double-blind, placebo-controlled, crossover design with counterbalancing was used, in which 36 healthy men and women participated in four experimental conditions involving the ingestion of placebo or caffeine three times daily for 6 days, followed by a seventh (‘challenge’) day of placebo or caffeine ingestion. Results: When caffeine was consumed on the challenge day, blood pressure was found to be elevated immediately after caffeine ingestion and was either unchanged or decreased (hypotensive effect) after a period of abstinence from the drug. Some diminution of the peak pressor effects was found when participants ingested caffeine after habitual use of the drug (6.0/5.2 mmHg) compared with when they had been abstinent before the challenge day (7.7/6.8 mmHg). This diminution in the reaction was comparatively small, however, and pressor effects persisted on caffeine-challenge days even when caffeine was consumed on preceding days. Conclusion: Habitual consumption diminished, but did not eliminate, the pressor effects of caffeine. Considering the almost universal consumption of caffeine beverages, the persistent pressor effects of the drug could have important implications for cardiovascular health.

Individual differences in adaptation of cardiovascular responses to stress

Previous research has described patterns of adaptation of cardiovascular responses across prolonged or recurring stress. However, despite important implications for the study of reactivity, relatively little research has directly examined the antecedents or consequences of this adaptation. We present data showing that neuroticism, a personality trait associated with dispositional appraisals of stress, is associated with reductions in HR, CO, and TPR responses across stress exposures. Comparisons of reactivity curves suggest blunted initial stress responses among persons with high neuroticism, and higher initial responses followed by greater decreases among persons with low neuroticism. The data also suggest an association between adaptation of cardiovascular responses and myocardial hemodynamic responding. Such findings shed new light on previous studies detecting healthful correlates of short-term stress responding, and highlight the relevance of adaptation to future cardiovascular reactivity research.

Biochemical validation of self-reported caffeine consumption during caffeine fading

Increasing concern about caffeine as a drug with potential for abuse has resulted in the development of procedures for effecting reductions in caffeine consumption among heavy users. However, the reliability of reported findings may be questioned, since previous studies have relied on subject self-report as the principal measure of caffeine use. The present study employed bioanalytic methods for assessing the reliability of self-reported caffeine intake during a caffeine-fading regime. Twelve subjects, each with a history of heavy caffeine use, provided baseline, treatment, and follow-up blood samples which were assayed for caffeine and its major metabolites. General support was provided for the reliability of self-report as a measure of caffeine consumption. The general efficacy of caffeine fading was also supported, although there were indications that maintenance effects may have been over-estimated in previous studies.

Dietary Caffeine, Performance and Mood: Enhancing and Restorative Effects after Controlling for Withdrawal Reversal

This study aimed to determine whether sustained (i.e. dietary) use of caffeine has net effects on performance and mood compared with sustained abstinence, and whether dietary caffeine restores performance and mood adversely affected by sleep restriction. Participants (n = 96) alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for 4 consecutive weeks, while either rested or sleep restricted. Performance involved either a single task requiring sustained vigilance or a varied battery of brief psychomotor and cognitive tasks, and mood was assessed using the Profile of Mood States. Caffeine had no significant net enhancing effects for either performance or mood when participants were rested, and produced no net restorative effects when performance and mood were degraded by sleep restriction.