Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis
Jozo Grgic1, Eric T Trexler23, Bruno Lazinica4, Zeljko Pedisic1Affiliationsexpand
PMID: 29527137
PMCID: PMC5839013
DOI: 10.1186/s12970-018-0216-0
Free PMC article
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.
The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials
Reza Tabrizi1, Parvane Saneei2, Kamran B Lankarani3, Maryam Akbari1, Fariba Kolahdooz4, Ahmad Esmaillzadeh25, Somayyeh Nadi-Ravandi6, Majid Mazoochi7, Zatollah Asemi8Affiliationsexpand
PMID: 30335479
DOI: 10.1080/10408398.2018.1507996
Abstract
This systematic review and meta-analysis of randomized controlled trials (RCTs) was performed to summarize the effect of caffeine intake on weight loss. We searched the following databases until November 2017: MEDLINE, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials. The relevant data were extracted and assessed for quality of the studies according to the Cochrane risk of bias tool. We estimated an intake-status regression coefficient (Beta) for each primary study and estimated the overall pooled Beta and SE using random effects meta-analysis on a double-log scale. Heterogeneity between studies was assessed by the Cochran Q statistic and I-squared tests (I2). Thirteen RCTs with 606 participants were included in the meta-analyses. The overall pooled Beta for the effect of caffeine intake was 0.29 (95%CI: 0.19, 0.40; Q = 124.5, I2 = 91.2%) for weigh, 0.23 (95%CI: 0.09, 0.36; Q = 71.0, I2 = 93.0%) for BMI, and 0.36 (95% CI: 0.24, 0.48; Q = 167.36, I2 = 94.0%) for fat mass. For every doubling in caffeine intake, the mean reduction in weight, BMI, and fat mass increased 2 Beta-fold (20.29 = 1.22, 20.23 = 1.17, and 20.36 = 1.28), which corresponding to 22, 17, and 28 percent, respectively. Overall, the current meta-analysis demonstrated that caffeine intake might promote weight, BMI and body fat reduction.
The Effect of Acute Caffeine Ingestion on Endurance Performance: A Systematic Review and Meta-Analysis
Kyle Southward1, Kay J Rutherfurd-Markwick23, Ajmol Ali45Affiliationsexpand
PMID: 29876876
DOI: 10.1007/s40279-018-0939-8
Erratum in
Abstract
Background: Caffeine is a widely used ergogenic aid with most research suggesting it confers the greatest effects during endurance activities. Despite the growing body of literature around the use of caffeine as an ergogenic aid, there are few recent meta-analyses that quantitatively assess the effect of caffeine on endurance exercise.
Objectives: To summarise studies that have investigated the ergogenic effects of caffeine on endurance time-trial performance and to quantitatively analyse the results of these studies to gain a better understanding of the magnitude of the ergogenic effect of caffeine on endurance time-trial performance.
Methods: A systematic review was carried out on randomised placebo-controlled studies investigating the effects of caffeine on endurance performance and a meta-analysis was conducted to determine the ergogenic effect of caffeine on endurance time-trial performance.
Results: Forty-six studies met the inclusion criteria and were included in the meta-analysis. Caffeine has a small but evident effect on endurance performance when taken in moderate doses (3-6 mg/kg) as well as an overall improvement following caffeine compared to placebo in mean power output (3.03 ± 3.07%; effect size = 0.23 ± 0.15) and time-trial completion time (2.22 ± 2.59%; effect size = 0.41 ± 0.2). However, differences in responses to caffeine ingestion have been shown, with two studies reporting slower time-trial performance, while five studies reported lower mean power output during the time-trial.
Conclusion: Caffeine can be used effectively as an ergogenic aid when taken in moderate doses, such as during sports when a small increase in endurance performance can lead to significant differences in placements as athletes are often separated by small margins.
Caffeine and Cognitive Functions in Sports: A Systematic Review and Meta-Analysis
Jorge Lorenzo Calvo1, Xueyin Fei2, Raúl Domínguez34, Helios Pareja-Galeano2Affiliationsexpand
PMID: 33800853
PMCID: PMC8000732
DOI: 10.3390/nu13030868
Free PMC article
Abstract
Cognitive functions are essential in any form of exercise. Recently, interest has mounted in addressing the relationship between caffeine intake and cognitive performance during sports practice. This review examines this relationship through a structured search of the databases Medline/PubMed and Web of Science for relevant articles published in English from August 1999 to March 2020. The study followed PRISMA guidelines. Inclusion criteria were defined according to the PICOS model. The identified records reported on randomized cross-over studies in which caffeine intake (as drinks, capsules, energy bars, or gum) was compared to an identical placebo situation. There were no filters on participants' training level, gender, or age. For the systematic review, 13 studies examining the impacts of caffeine on objective measures of cognitive performance or self-reported cognitive performance were selected. Five of these studies were also subjected to meta-analysis. After pooling data in the meta-analysis, the significant impacts of caffeine only emerged on attention, accuracy, and speed. The results of the 13 studies, nevertheless, suggest that the intake of a low/moderate dose of caffeine before and/or during exercise can improve self-reported energy, mood, and cognitive functions, such as attention; it may also improve simple reaction time, choice reaction time, memory, or fatigue, however, this may depend on the research protocols.
Muscular Endurance and Muscular Strength in Women: A Meta-Analysis
Jozo Grgic1, Juan Del Coso2Affiliationsexpand
PMID: 34072182
PMCID: PMC8199301
DOI: 10.3390/ijerph18115773
Free PMC article
Abstract
This meta-analysis aimed to explore the effects of caffeine ingestion on muscular endurance and muscular strength in women. Five databases were searched to find relevant studies. A random-effects meta-analysis of standardized mean differences (SMD) was performed for data analysis. Subgroup meta-analyses explored the effects of caffeine on upper-body and lower-body muscular endurance and muscular strength. Eight crossover placebo-controlled studies were included in the review. In the main meta-analysis that considered data from all included studies, there was a significant ergogenic effect of caffeine on muscular endurance (SMD = 0.25; p = 0.027) and muscular strength (SMD = 0.18; p < 0.001). In a subgroup analysis that considered only upper-body exercises, there was a significant ergogenic effect of caffeine on muscular endurance (SMD = 0.20; p = 0.007) and muscular strength (SMD = 0.17; p < 0.001). In a subgroup analysis that considered only lower-body exercises, there was no significant difference between caffeine and placebo for muscular endurance (SMD = 0.43; p = 0.092) or muscular strength (SMD = 0.16; p = 0.109). The main finding of this meta-analysis is that caffeine ingestion has a significant ergogenic effect on muscular endurance and muscular strength in women. The effects reported in this analysis are similar to those previously observed in men and suggest that women may use caffeine supplementation as an ergogenic aid for muscular performance. Future research is needed to explore the effects of caffeine on lower-body muscular endurance and muscular strength in this population.
Coffee and caffeine consumption and depression: A meta-analysis of observational studies
Longfei Wang1, Xiaoli Shen1, Yili Wu1, Dongfeng Zhang2Affiliationsexpand
PMID: 26339067
DOI: 10.1177/0004867415603131
Abstract
Objective: The results from observation studies on the relationship between coffee intake and risk of depression and the relationship between caffeine consumption and depression remain controversial. We conducted a meta-analysis with a dose-response analysis to quantitatively summarize the evidence about the association between coffee and caffeine intakes and risk of depression.
Method: Relevant articles were identified by researching PubMed, Web of Science, China National Knowledge Infrastructure and WANFANG DATA in English or Chinese from 1 January 1980 to 1 May 2015. Case-control, cohort or cross-sectional studies evaluating coffee or caffeine consumption and depression were included. A random-effects model was used to combine study-specific relative risk and 95% confidence interval. Dose-response relationship was assessed by restricted cubic spline functions.
Results: Data were obtained from 11 observation articles; 330,677 participants from seven studies in seven articles were included in the coffee-depression analysis, while 38,223 participants from eight studies in seven articles were involved in the caffeine-depression analysis. Compared with the lowest level consumption, the pooled relative risk (95% confidence interval) for coffee-depression and caffeine-depression was 0.757 [0.624, 0.917] and 0.721 [0.522, 0.997], respectively. For dose-response analysis, evidence of a linear association was found between coffee consumption and depression, and the risk of depression decreased by 8% (relative risk = 0.92, 95% confidence interval = [0.87, 0.97], p = 0.002) for each cup/day increment in coffee intake; a nonlinear association was found between caffeine consumption and depression, the risk of depression decreased faster and the association became significant when the caffeine consumption was above 68 mg/day and below 509 mg/day.
Conclusions: Coffee and caffeine consumption were significantly associated with decreased risk of depression.
