1.
Caffeine and attentional control: improved and impaired performance in healthy older adults and Parkinson's disease according to task demands.
Sharma, K, Fallon, SJ, Davis, T, Ankrett, S, Munro, G, Christopher, G, Coulthard, E
Psychopharmacology. 2022;239(2):605-619
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Plain language summary
Impairments in goal-directed attention are a frequent problem in older adults but these problems become magnified in neurodegenerative conditions like Parkinson's disease (PD). Although symptomatic treatment of PD focuses on motor deficits, cognitive deficits can be disabling, even in the early stages. This study is a single-blind, cross-over trial which compared the effect of a tablet containing 100-mg caffeine (Proplus) which was dissolved in instant decaffeinated coffee. Twenty-four PD patients and forty-four aged matched healthy elderly participants (controls) were enrolled in the study. Results show that caffeine: - did not affect attention in a unitary manner, across all attentional networks. In fact, the effect of caffeine on cognitive performance depended greatly upon the specific task requirements. - improved accuracy on the choice reaction time task. - improved accuracy of response selection in both the congruent and incongruent conditions. Authors conclude that caffeine’s overall attentional effects put forward by their study should be considered neither exclusively positive nor detrimental but instead conditional on task demands.
Abstract
INTRODUCTION Caffeine is frequently consumed to boost goal-directed attention. These procognitive effects may occur due to the adenosine-mediated enhancement of monoamines, such as dopamine, after caffeine administration. As such, caffeine's beneficial effects may be altered in conditions such as Parkinson's disease (PD). However, whether caffeine improves cognition, and at what cost, has not been experimentally established in patients with neurodegenerative disease. METHODS Single-dose trials to probe cognitive effects of caffeine are often confounded by short-term caffeine abstinence which conflates caffeine's effects with treatment of withdrawal. Using a placebo controlled, blinded, randomised trial design, we assessed the effect of 100 mg of caffeine across well-established tasks (Choice reaction time, Stroop Task and Rapid Serial Visual Presentation Task; RSVP) that probe different aspects of attention in PD patients (n = 24) and controls (n = 44). Critically, participants withdrew from caffeine for a week prior to testing to eliminate the possibility that withdrawal reversal explained any cognitive benefit. RESULTS Caffeine administration was found to reduce the overall number of errors in patients and controls on the Stroop (p = .018, η2p = .086) and Choice reaction time (p < . 0001, η2p = .588) tasks, but there was no specific effect of caffeine on ignoring irrelevant information in the Stroop task. On the RSVP task, caffeine improved dual item accuracy (p = .037) but impaired single item accuracy (p = .044). Across all tasks, there was little evidence that caffeine has different effects in PD participants and controls. CONCLUSION When removing withdrawal effects as a factor, we demonstrate caffeine has beneficial effects on selective attention but is a double-edge sword for visual temporal attention and would need careful targeting to be clinically useful.
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Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis.
Grgic, J, Trexler, ET, Lazinica, B, Pedisic, Z
Journal of the International Society of Sports Nutrition. 2018;15:11
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The possible physical performance enhancing (or 'ergogenic) effects of caffeine have been extensively studied since the early 1900s. Recent focus has shifted to its impact on anaerobic physical performance outcomes such as muscular strength, endurance and jumping tasks that require power. Although it has been found to enhance muscle endurance, less is known about its impact on strength and power. This is the first meta-analysis on caffeine and muscle power, and includes 20 studies - ten on muscle strength outcomes and ten on muscle power. The analysis found that caffeine significantly improves muscle strength (SMD = 0.20; 95% confidence interval [CI]: 0.03, 0.36; p = 0.023) but only for upper and not lower body strength. These results were found for men but more robust studies are needed to examine the impact for women (although the limited research suggests there may be a positive impact). This is in contrast to a previous meta-analysis that found no impact of caffeine on muscle strength (Polito, Souza, Casonatto & Farinatti, 2016). It was also found to significantly improve muscle power (SMD = 0.17; 95% CI: 0.00, 0.34; p = 0.047). Although the pooled effect of caffeine on performance outcomes was small to medium, even small improvements can make a big difference competitively. Future research is needed to identify the best dosage and form of caffeine to maximise its performance enhancing effects. Additionally, more robust research is needed to reduce bias, and studies including women. It is important to recognise that individual physical performance changes as a result of caffeine are variable, so these findings must be applied on a case-by-case basis. * Polito MD, Souza DB, Casonatto J, Farinatti P. Acute effect of caffeine consumption on isotonic muscular strength and endurance: a systematic review and meta-analysis. Sci Sports. 2016;31:119–28.
Abstract
BACKGROUND Caffeine is commonly used as an ergogenic aid. Literature about the effects of caffeine ingestion on muscle strength and power is equivocal. The aim of this systematic review and meta-analysis was to summarize results from individual studies on the effects of caffeine intake on muscle strength and power. METHODS A search through eight databases was performed to find studies on the effects of caffeine on: (i) maximal muscle strength measured using 1 repetition maximum tests; and (ii) muscle power assessed by tests of vertical jump. Meta-analyses of standardized mean differences (SMD) between placebo and caffeine trials from individual studies were conducted using the random effects model. RESULTS Ten studies on the strength outcome and ten studies on the power outcome met the inclusion criteria for the meta-analyses. Caffeine ingestion improved both strength (SMD = 0.20; 95% confidence interval [CI]: 0.03, 0.36; p = 0.023) and power (SMD = 0.17; 95% CI: 0.00, 0.34; p = 0.047). A subgroup analysis indicated that caffeine significantly improves upper (SMD = 0.21; 95% CI: 0.02, 0.39; p = 0.026) but not lower body strength (SMD = 0.15; 95% CI: -0.05, 0.34; p = 0.147). CONCLUSION The meta-analyses showed significant ergogenic effects of caffeine ingestion on maximal muscle strength of upper body and muscle power. Future studies should more rigorously control the effectiveness of blinding. Due to the paucity of evidence, additional findings are needed in the female population and using different forms of caffeine, such as gum and gel.