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Caffeine

Caffeine and coffee interventions for alertness, focus, and sustained energy.

Research synthesis3 min read

What the Caffeine Research Actually Shows

Caffeine is the most studied psychoactive substance on earth. The research is unusually clear — here's what it actually shows about performance, timing, and tolerance.

The Most Studied Stimulant in the World

Caffeine has an unusually good evidence base — it's cheap, legal, widely consumed, and easy to study in controlled conditions. The result is hundreds of high-quality RCTs with consistent findings. Most people's caffeine habits are poorly calibrated relative to what the research supports.

What Replicates Strongly

Caffeine reliably improves sustained attention, reaction time, and vigilance. The effect is robust across doses of 100–400mg, study designs, and populations. The dose-response curve is roughly linear up to about 300mg, after which additional gains are smaller and side effects increase. For cognitive work requiring sustained focus, caffeine is one of the few interventions with a genuine, large effect.

The half-life is 5–6 hours on average — longer than most people assume. A 200mg dose (roughly a large coffee) at 2pm leaves approximately 100mg active at 8pm and 50mg at 1am. Polysomnography studies show that late-afternoon caffeine degrades slow-wave sleep even when subjects report sleeping fine. Individual half-life varies 2–10 hours based on CYP1A2 genotype, liver function, and oral contraceptive use.

A "caffeine nap" outperforms caffeine or a nap alone. Drinking coffee then immediately napping for 20 minutes times the caffeine peak to hit just as you wake, producing better alertness scores than either intervention alone. The mechanism: adenosine (which caffeine blocks) clears during the nap, leaving caffeine receptors uncontested when you wake.

Tolerance develops within days of regular use. Daily caffeine use produces near-complete tolerance to subjective alertness effects within 7–12 days. The implication: habitual caffeine users are mostly restoring baseline rather than enhancing above it. Strategic use — with regular breaks — preserves efficacy.

Timing Is More Important Than Dose

The "delay your first coffee 90 minutes after waking" recommendation has a mechanistic basis: adenosine accumulates during sleep and continues clearing for 60–90 minutes after waking. Blocking its clearance with early caffeine may reduce the natural cortisol-driven alertness peak. Some RCT evidence supports this, though effect sizes are modest.

The more impactful timing question is the cutoff. Studies measuring objective sleep architecture (not just subjective quality) consistently support a caffeine cutoff of 12–2pm for most people — though individual variation is large.

What the Research Can't Tell You

Your optimal dose, timing, and cutoff depend on your CYP1A2 genotype, sleep architecture, and baseline adenosine sensitivity — none of which you can read from the literature. The averages are a starting point. Your own data is more actionable.

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Effect of Caffeine on Attention and Alertness Measured in a Home-Setting, Using Web-Based Cognition Tests

This study found that caffeine significantly improved reaction times on a web-based attention test when taken at home, demonstrating that personal experiments using online tools can reliably measure cognitive effects.

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Evidence base

Min quality:

50 papers

RCTWikiHigh evidence score

Music improves sleep quality in older adults

Hui‐Ling Lai, Marion Good · Journal of Advanced Nursing · 2005 · 245 citations

Listening to soft, sedative music at bedtime for at least three weeks can significantly improve subjective sleep quality and its components (like falling asleep faster and sleeping longer) in older adults experiencing sleep difficulties, suggesting a promising non-pharmacological intervention for self-experimentation.

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ObservationalLeading journalWikiModerate

To Dope or Not to Dope: Neuroenhancement with Prescription Drugs and Drugs of Abuse among Swiss University Students

Larissa J. Maier, Matthias E. Liechti, Fiona Herzig +1 more · PLoS ONE · 2013 · 193 citations

About 14% of Swiss university students have used prescription drugs (like Ritalin) or drugs of abuse (including alcohol) at least once specifically to boost their academic performance, but daily use is rare and most use happens sporadically before exams—meaning the "epidemic" of cognitive doping is more about occasional experimentation than chronic abuse.

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RCTWikiModerate

Music improves sleep quality in older adults

Hui‐Ling Lai, Marion Good · Journal of Advanced Nursing · 2006 · 59 citations

Listening to 45 minutes of soft, sedative music before bed for three weeks significantly improved multiple aspects of sleep quality in older adults with sleep difficulties, suggesting a simple, non-pharmacological intervention worth testing for personal sleep improvement.

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StudyModerate

Caffeine Consumption through Coffee: Content in the Beverage, Metabolism, Health Benefits and Risks

Juliana DePaula, Adriana Farah · Beverages · 2019 · 214 citations

Caffeine (1,3,7-trimethylxanthine) is the most consumed psychoactive substance in the world, acting by means of antagonism to adenosine receptors, mainly A1 and A2A. Coffee is the main natural source of the alkaloid which is quite soluble and well extracted during the brew’s preparation. After consumption, caffeine is almost completely absorbed and extensively metabolized in the liver by phase I (cytochrome P450) enzymes, mainly CYP1A2, which appears to be polymorphically distributed in human populations. Paraxanthine is the major caffeine metabolite in plasma, while methylated xanthines and methyluric acids are the main metabolites excreted in urine. In addition to stimulating the central nervous system, caffeine exerts positive effects in the body, often in association with other substances, contributing to prevention of several chronic diseases. The potential adverse effects of caffeine have also been extensively studied in animal species and in humans. These aspects will be approached in the present review.

StudyLeading journalModerate

Are the Current Guidelines on Caffeine Use in Sport Optimal for Everyone? Inter-individual Variation in Caffeine Ergogenicity, and a Move Towards Personalised Sports Nutrition

Craig Pickering, John Kiely · Sports Medicine · 2017 · 196 citations

Caffeine use is widespread in sport, with a strong evidence base demonstrating its ergogenic effect. Based on existing research, current guidelines recommend ingestion of 3-9 mg/kg approximately 60 min prior to exercise. However, the magnitude of performance enhancement following caffeine ingestion differs substantially between individuals, with the spectrum of responses ranging between highly ergogenic to ergolytic. These extensive inter-individual response distinctions are mediated by variation in individual genotype, environmental factors, and the legacy of prior experiences partially mediated via epigenetic mechanisms. Here, we briefly review the drivers of this inter-individual variation in caffeine response, focusing on the impact of common polymorphisms within two genes, CYP1A2 and ADORA2A. Contemporary evidence suggests current standardised guidelines are optimal for only a sub-set of the athlete population. Clearer understanding of the factors underpinning inter-individual variation potentially facilitates a more nuanced, and individually and context-specific customisation of caffeine ingestion guidelines, specific to an individual's biology, history, and competitive situation. Finally, we identify current knowledge deficits in this area, along with future associated research questions.

RCTLeading journalWikiHigh evidence score

Acute beneficial effects of a functional energy shot on cognitive performance and mood states during cognitively demanding task performance: a randomized, double-blind, placebo-controlled, crossover trial

Olivia K. O’Shea, Nathan Lawley, Anna Azzopardi +5 more · Frontiers in Nutrition · 2025 · 3 citations

This study found that a functional energy shot acutely improved various aspects of cognitive performance and mood, such as alertness, energy, and working memory speed, while reducing mental fatigue, suggesting it could be a useful tool for self-experimenters looking to boost focus and mood during demanding tasks.

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ObservationalWikiModerate

Caffeine and Taurine from Energy Drinks—A Review

Tania Mihăiescu, Sabina Turti, Marius Souca +6 more · Cosmetics · 2024 · 13 citations

This narrative review found that energy drinks containing caffeine and taurine produce mixed effects on skin health, cardiovascular function, sleep, and cognition—with benefits in some populations (e.g., improved exercise capacity in athletes, migraine relief in children) but clear harms in others (e.g., elevated blood pressure, liver and kidney damage, poor sleep quality in adolescents)—but the evidence is too weak and inconsistent to draw firm conclusions for personal experimentation.

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StudyModerate

Caffeine Consumption, Sleep, and Affect in the Natural Environments of Depressed Youth and Healthy Controls

Diana J. Whalen, Jennifer S. Silk, M. Semel +5 more · Journal of Pediatric Psychology · 2007 · 82 citations

OBJECTIVE: Sleep problems are a cardinal symptom of depression in children and adolescents and caffeine use is a prevalent and problematic issue in youth; yet little is known about caffeine use and its effects on sleep in youth with depression. We examined caffeine use and its relation to sleep and affect in youth's natural environments. METHODS: Thirty youth with major depressive disorder (MDD) and 23 control youth reported on caffeine use, sleep, and affect in their natural environment using ecological momentary assessment at baseline and over 8 weeks, while MDD youth received treatment. RESULTS: Youth with MDD reported more caffeine use and sleep problems relative to healthy youth. Youth with MDD reported more anxiety on days they consumed caffeine. Caffeine use among youth with MDD decreased across treatment, but sleep complaints remained elevated. CONCLUSIONS: Findings suggest that both sleep quality and caffeine use are altered in pediatric depression; that caffeine use, but not sleep problems, improves with treatment; and that caffeine may exacerbate daily anxiety among youth with depression.

StudyModerate

Acute effects of brewed cocoa consumption on attention, motivation to perform cognitive work and feelings of anxiety, energy and fatigue: a randomized, placebo-controlled crossover experiment

Ali Boolani, Jacob B. Lindheimer, Bryan D. Loy +2 more · BMC Nutrition · 2017 · 47 citations

Acute effects of caffeinated and non-caffeinated cocoa on mood, motivation, and cognitive function are not well characterized. The current study examined the acute influence of brewed cocoa, alone and with supplemental caffeine, on attention, motivation to perform cognitive tasks and energy and fatigue mood states. A randomized, double-blinded, within-subjects crossover trial was conducted with four 473-milliliter brewed beverage treatments: cocoa, caffeinated cocoa (70 milligrams caffeine total), placebo (flavored and colored brewed water) and positive control (placebo plus 66 milligrams caffeine, “caffeine alone”). Participants (n = 24) were low consumers of polyphenols without elevated feelings of energy. Before and three times after beverage consumption, a 26-minute battery was used to assess motivation to perform cognitive tasks, mood and attention (serial subtractions of 3 and 7, the continuous performance task, and the Bakan dual task) with a 10-minute break between each post-consumption battery. The procedure was repeated with each beverage for each participant at least 48 h apart and ±30 min the same time of day. Data were evaluated using Treatment X Time analysis of covariance controlling for hours of prior night’s sleep. Compared to placebo, cocoa reduced overall false alarm errors progressively across time with 0.92, 1.44 and 2.35 fewer false alarms on average 22–48, 60–86 and 98–124 min post-consumption (η 2 = 0.08, p = 0.019). Caffeinated cocoa: (i) attenuated the anxiety-provoking effects of cognitive testing found after drinking caffeine alone (η 2 = 0.064, p = 0.038), and (ii) increased accuracy (η 2 = 0.085, p = 0.01) and reduced omission errors (η 2 = 0.077, p = 0.016) on the Bakan primary task compared to cocoa alone. Brewed cocoa can acutely reduce errors associated with attention in the absence of changes in either perceived motivation to perform cognitive tasks or feelings of energy and fatigue. Supplemental caffeine in brewed cocoa can enhance aspects of attention while brewed cocoa can attenuate the anxiety-provoking effects found from drinking caffeine alone. ClinicalTrials.gov Identifier: NCT01651793 . Registered July 25, 2012.

ObservationalLeading journalWikiModerate

The Relationship Between Caffeine Consumption and Depression, Anxiety, Stress Level and Sleep Quality in Medical Students

İrem AKOVA, Elif Nur Duman, Ayça Elçim Sahar +1 more · Journal of Turkish Sleep Medicine · 2023 · 12 citations

Medical students who reported higher anxiety and stress scores also consumed more caffeine, and 73.1% of students had poor sleep quality — with worse sleep linked to higher caffeine intake — but this cross-sectional study cannot tell us whether caffeine causes these problems or whether students use caffeine to cope with them.

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ObservationalWikiModerate

Factors Affecting Sleep Quality among Adolescent Athletes

Hoi Man Lo, Joyce Hoi Yee Leung, Gavin Ka Yin Chau +3 more · Sports Nutrition and Therapy · 2017 · 16 citations

Adolescent team-sport athletes in Hong Kong who consumed caffeine or alcohol, experienced extreme moods before bed, or slept in bright/noisy environments reported significantly worse sleep quality; academic anxiety was a stronger predictor of poor sleep than sports-related anxiety, and the average sleep duration was below recommended levels for this age group.

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StudyLeading journalModerate

Caffeine-Containing, Adaptogenic-Rich Drink Modulates the Effects of Caffeine on Mental Performance and Cognitive Parameters: A Double-Blinded, Placebo-Controlled, Randomized Trial

Ali Boolani, Daniel T. Fuller, Sumona Mondal +3 more · Nutrients · 2020 · 24 citations

= 0.098) increased systolic BP 30 min post consumption (still within normal healthy ranges). The caffeine beverage also led to an improvement in most cognitive measures and moods 30-min post-consumption with improvements tapering at 69 and 108 min, while e+ shot noted more steady improvements with no significant differences between beverages on most cognitive and mood measures at 69 and 108 min. However, compared to caffeine, e+ shot noted a significant increase in reaction time at 108 min, while caffeine noted a small change in the opposite direction. No side-effects were reported by any intervention. These results suggest that the specific blend of adaptogens in e+ shot may modulate the neurocognitive effects of caffeine on mood, and cognition.

StudyLeading journalModerate

“No Thanks, It Keeps Me Awake”: The Genetics of Coffee-Attributed Sleep Disturbance

Michelle Luciano, Ghu Zhu, Katherine M. Kirk +4 more · SLEEP · 2007 · 38 citations

STUDY OBJECTIVES: Previous genetic investigations of sleep disturbance have shown various measures of sleep quality and sleep pattern to be heritable. But none of these studies have investigated the genetic predisposition to sleep disturbance attributed to caffeine. In this study, the heritability of coffee-attributed sleep disturbance and its relationship with other sleep measures were estimated, and chromosomal regions influencing this trait were identified. DESIGN: A classical twin design was used to estimate the heritability of coffee-attributed sleep disturbance and its genetic covariance with other measures of sleep disturbance (e.g., due to anxiety, depression) and sleep quality (e.g., variability in sleep quality). To locate quantitative trait loci influencing coffee-attributed sleep disturbance, a genome-wide linkage screen of 1395 microsatellite markers was performed. PARTICIPANTS: The study included 3808 Australian adult twin pairs (n = 1799 monozygous pairs; n = 2009 dizygous pairs). A subsample of 1989 individuals from 1175 families was used for the linkage analysis. MEASUREMENTS AND RESULTS: The heritability of coffee-attributed sleep disturbance (measured by self report) was approximately 0.40, with three fourths of this genetic variance explained by genes unrelated to the general sleep disturbance factor. One region of significant linkage to coffee-attributed sleep disturbance was identified on chromosome 2q (LOD score of 2.9). CONCLUSIONS: Although no candidate genes known to be related to caffeine metabolism or sleep disorder were identified in the significant linkage region, 2 candidates were found under a smaller peak on chromosome 17q.

StudyModerate

Bidirectional Associations Between Sleep and Anxiety Symptoms in Emerging Adults in a Residential College Setting

Jack S. Peltz, Ronald D. Rogge, Cameron P. Pugach +1 more · Emerging Adulthood · 2016 · 29 citations

Daily covariation of three sleep indicators (quantity, quality, postsleep restedness), anxiety symptoms, and caffeine and alcohol consumption was observed in 283 emerging adults ( M age = 19.9). Participants completed web-based sleep diary surveys every morning and evening for 7 consecutive days. Cross-lagged models suggested that sleep quality and restedness (reported each morning) predicted students’ anxiety levels (reported each evening) and that anxiety levels predicted all three sleep indicators. Furthermore, pre-bedtime caffeine consumption predicted worse sleep that night. Controlling for the effects of weekdays versus weekends produced virtually identical effects to the 7-day models, although weekend alcohol consumption emerged as a predictor of postsleep restedness. These data support bidirectionality between sleep and anxiety symptoms in emerging adults attending college/university and highlight potential avenues for intervention.

StudyModerate

The Effect of Coffee and Caffeine on Mood, Sleep, and Health-Related Quality of Life

Brian Distelberg, Andrea Staack, K'dee D. Elsen +1 more · Journal of Caffeine Research · 2017 · 27 citations

Objective: The study sought to measure the effects of caffeinated and decaffeinated coffee on affective mood, sleep, and health-related quality of life (HRQL). Methods: Forty-nine healthy participants between the ages of 18 and 45 took part in a randomized, double-blind, longitudinal study with decaffeinated coffee as the control. The participants began with a 5-day washout period, followed by a 5-day treatment phase, and concluded with a 5-day washout phase. Data were analyzed with repeated-measures analysis of covariance and ordinary least-squares mediational analysis. Results: The caffeinated coffee treatment group showed significant direct effects on sleep, anxiety, and stress-based domains of HRQL. In addition, mediational analysis showed that the more global domains of HRQL were affected indirectly through reduced sleep quality/quantity and through increases in anxiety. No significant changes were noted in the decaffeinated treatment group. Conclusions: Given the strong effect of caffeine on sleep and anxiety, as well as the indirect effect on HRQL in this study, it might be beneficial for individuals with stress responsive illnesses to refrain from high doses of caffeine. Further studies should examine the effects of caffeine in individuals with various stress-related illnesses. The results of caffeine on depression are contrary to previous studies, and further evaluations should examine variations of effects based on dosages and different populations (major depression diagnoses as well as healthy populations).

StudyModerate

Revving Up and Staying Up: Energy Drink Use Associated with Anxiety and Sleep Quality in a College Sample

Michael J. Stasio, K. Curry, Alexandra L. Wagener +1 more · College student journal · 2011 · 21 citations

Associations among caffeinated energy drink use, anxiety, and sleep quality were examined in a young adult sample (N = 107). A 7-day retrospective survey methodology was used to assess consumption rates among college student athletes, ROTC cadets, and those in a control group. Regression analyses revealed that energy drink use explained 29% of the variance in anxiety scores and 20% in sleep disturbance scores. Greater frequency of energy drink use was associated with poorer sleep quality, longer sleep latency, shorter sleep duration, and lower habitual sleep efficiency. No group differences in energy drink consumption were revealed. More research into the effects of energy drink use on psychological adjustment variables appears warranted. Keywords: energy drinks; caffeine; anxiety; sleep quality; college students ********** Energy drink use appears to be ubiquitous, particularly among young adults, who may expect these products to improve concentration and performance, combat fatigue, or even to counteract the effects of alcohol intoxication. Data examining the prevalence and pattern of energy drink consumption, as well as the potential risks, have emerged (Malinauskas, Aeby, Overton, Carpenter-Aeby, & Barber-Heidal, 2007; Oteri, Caputi, & Calapai, 2007; Miller, 2008). For example, recent survey data from 602 college students found that frequency of energy drink use was positively related to marijuana use, sexual and other risk-taking, fighting, and failure to wear a seatbelt (Miller, 2008). Few studies have examined relationships among energy drink use and psychological adjustment variables, such as anxiety and sleep quality. A secondary goal was to examine use frequencies in certain subgroups--athletes and ROTC cadets--who regularly participate in physically demanding co-curricula activities. Caffeine, Anxiety, and Sleep While energy drinks often contain ingredients such as taurine, glucose, carbohydrates, herbal extracts, and B vitamins, caffeine has been the most studied in relation to anxiety and sleep. A central nervous system (CNS) and cardiac stimulant, caffeine acts as an antagonist to adenosine, a substance that has been shown to promote sleep and to influence autonomic nervous system arousal (Alsene, Deckert, Sand, & de Wit, 2003; Roehrs & Roth, 2008). Moderate doses of 75 to 200 mg improve attention, alertness, and visual vigilance, reduce fatigue and shorten reaction times, and improve subjective mood states (Childs & de Wit, 2008; Herz, 1999; Lieberman, Tharion, Shukitt-Hale, Speckman, & Tulley, 2002; Smith, 2002). Habitual caffeine use, however, may moderate these effects (Hamleers, et al., 2000). Caffeine may also exacerbate pre-existing cardiac conditions and have side effects such as increased heart rate and palpitations, elevated blood pressure, and restlessness. Consumption of caffeine in higher quantities prompts anxiety-related responses. Veleber and Templer (1984) found that 65% participants who received a 300 mg dose of caffeine showed significant increases in anxiety scores from pre- to post-test controlling for weight and daily caffeine use. Telch, Silverman, and Schmidt (1996) reported that 400 mg or more of caffeine increases autonomic nervous system arousal, respiration rate, oxygen intake, and carbon dioxide elimination, as well as prompts negative somatic sensations, such as shaking and trembling. However, Smith (2002) has questioned the ecological validity of such studies based on evidence that caffeine users do not typically ingest large amounts of caffeine all at once, but rather self-regulate their intake throughout the day to avoid negative side effects and sleep disturbances. Laboratory data has demonstrated links between caffeine use and sleep. Studies utilizing polysomnography have generally shown that caffeine prior to bedtime may increase sleep onset latency, decrease total sleep time, lower sleep efficiency, and reduce slow-wave sleep (Paterson, Nutt, Ivarsson, Hutson, & Wilson, 2009; Landolt, Werth, Borbely, & Dijk, 1995). …

StudyModerate

Effects of Different Sources of Low-Dose Caffeine on Mood/Arousal and Cognitive Performance

Christopher Irwin, Danielle McCartney, Gary Grant +4 more · Perceptual and Motor Skills · 2022 · 8 citations

In this study we investigated the effects of variously derived sources of low-dose caffeine on mood/arousal and cognitive performance. Twenty-two participants (15 men, 7 women; M age: 28.2, SD = 9.0 years) undertook five randomized, crossover trials in which they consumed either a water control (CON) or 80 mg of caffeine from one of four sources (coffee [COF], energy drink [END], capsule [CAP], and dissolvable mouth strip [STR]). We measured the participants’ perceived efficacy of these varied caffeine sources pre-treatment; and we measured mood/arousal at pre-treatment, and again at 15 and 45 minutes post-treatment. We also measured choice reaction-time at 15 and 45 minutes post-treatment, and participants completed the psychomotor vigilance task (PVT) 45 minutes post-treatment. Caffeine increased participant ratings of alertness and decreased their ratings of tiredness irrespective of source ( p’s < .05), and all sources of caffeine decreased reaction time on the PVT ( p’s < .05), with ex-Gaussian distributional analysis localizing this to the tau-parameter, indicating lower variability. However, only the COF source was associated with improved ‘overall mood’ ( p’s < .05). Participants expected to perform better on the PVT with COF compared to CON, but there were no other significant associations between source expectancy and performance. In sum, a modest dose of caffeine, regardless of source, positively impacted mood/arousal and cognitive performance, and these effects did not appear to be influenced by expectations.

StudyModerate

Effectiveness of caffeine and blue-enriched light on cognitive performance and electroencephalography correlates of alertness in a spaceflight robotics simulation

Erin E. Flynn‐Evans, Melanie Rueger, Andrew Liu +4 more · npj Microgravity · 2023 · 5 citations

Human cognitive impairment associated with sleep loss, circadian misalignment and work overload is a major concern in any high stress occupation but has potentially catastrophic consequences during spaceflight human robotic interactions. Two safe, wake-promoting countermeasures, caffeine and blue-enriched white light have been studied on Earth and are available on the International Space Station. We therefore conducted a randomized, placebo-controlled, cross-over trial examining the impact of regularly timed low-dose caffeine (0.3 mg per kg per h) and moderate illuminance blue-enriched white light (~90 lux, ~88 melEDI lux, 6300 K) as countermeasures, separately and combined, in a multi-night simulation of sleep-wake shifts experienced during spaceflight among 16 participants (7 F, ages 26-55). We find that chronic administration of low-dose caffeine improves subjective and objective correlates of alertness and performance during an overnight work schedule involving chronic sleep loss and circadian misalignment, although we also find that caffeine disrupts subsequent sleep. We further find that 90 lux of blue-enriched light moderately reduces electroencephalogram (EEG) power in the theta and delta regions, which are associated with sleepiness. These findings support the use of low-dose caffeine and potentially blue-enriched white light to enhance alertness and performance among astronauts and shiftworking populations.

StudyModerate

Caffeine Consumption, Sleep Quality and Mental Health Outcomes Among Malaysian University Students

Norhaslina Sulaiman, Asma Ali, Muhamad Khairul Zakaria +3 more · National Journal of Community Medicine · 2024 · 5 citations

Background: Recognizing the scarcity of data on caffeine consumption among university students in Malaysia, this study was designed to first characterize the habitual caffeine intake within this group. This study further investigated the potential association between these caffeine consumption patterns and sleep quality and mental health status. Methodology: The study employed an online self-administered questionnaire to assess habitual caffeine intake from various products. Sleep quality and mental health were evaluated using the Pittsburgh Sleep Quality Index (PSQI) and the Depression, Anxiety, and Stress Scale-21 (DASS-21), respectively. Results: 78% of the respondents consumed caffeinated products daily within the safe level recommended by the European Food Safety Authority (£400mg/day). Only 2.6% of the students consumed caffeine exceeding the recommended limit. The median total daily caffeine intake was 100mg/day. Most students had poor sleep quality (77.3%), with 43.5%, 49.5%, and 33.0% reporting varying levels of depression, anxiety, and stress, respectively. Odds ratio calculations revealed respondents consuming less than or more than 400 mg/day of caffeine did not show significantly different odds of poor sleep quality, depression, anxiety, or stress compared to non-consumers. Conclusions: This study highlights the need for further localized research on caffeine's effects among Malaysian university students regarding caffeine consumption, sleep, and mental health.

StudyModerate

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

David G. Lassiter, Lynne Kammer, James Burns +4 more · Journal of Caffeine Research · 2012 · 8 citations

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.

StudyModerate

Differential Time-of-Day Effects of Caffeine Capsule and Mouth Rinse on Cognitive Performance in Adolescent Male Volleyball Athletes: A Randomized Crossover Investigation

Salma Belhaj Amor, Wissem Dhahbi, Houda Bougrine +5 more · Life · 2025 · 2 citations

Caffeine is widely used to enhance cognitive performance, but its efficacy may vary with the administration route and circadian timing. This study compared the acute effects of caffeine capsule ingestion and caffeine mouth rinsing on cognitive performance across morning, midday, and evening sessions in well-trained, adolescent male volleyball players. Twenty-four athletes completed three randomized, double-blind, crossover trials involving a caffeine capsule (3 mg·kg−1), a caffeine mouth rinse of the same dose (expectorated), and a placebo. Cognitive performance was assessed using simple and choice reaction time tests and the Stroop task, alongside a side-effects questionnaire. Both caffeine forms improved performance versus the placebo, with the greatest enhancements occurring at midday and moderate benefits evident in the morning. Capsule ingestion produced the most consistent improvements across reaction speed and executive control, whereas mouth rinsing elicited smaller, task-dependent effects, particularly at midday. No consistent or practically relevant benefits were observed for either caffeine condition in the evening, when cognitive performance was naturally highest. Side effects were mild and infrequent, with occasional headaches after capsule ingestion. These findings indicate that caffeine capsules most effectively enhance cognitive performance when baseline alertness is suboptimal, while caffeine mouth rinsing represents a practical ingestion-free alternative with moderate efficacy.

StudyModerate

Problematic coffee use and associated factors among medical and health science students in Dilla University, Ethiopia

Chalachew Kassaw, Rediet Regasa, Misrak Negash +5 more · SAGE Open Medicine · 2024 · 2 citations

Objective: Coffee holds a cherished place in Ethiopian culture, its consumption among students raises concerns despite its perceived benefits for alertness and productivity. Moderate caffeine intake remains unproblematic, but exceeding 400 mg daily can trigger detrimental health effects such as fatigue, memory impairment, and even attention-deficit disorder. Research on problematic coffee use among young adults, specifically Ethiopian students, remains limited, hindering our understanding of its potential scope and impact. To address this knowledge gap, researchers at Dilla University, Ethiopia, undertook a comprehensive study in 2022, focusing on the university's student population. This investigation holds significant potential to unveil the previously obscured landscape of excessive coffee consumption in this demographic and inform future research and potential interventions. Methodology: < 0.05 and 95% confidence interval was employed. Result: = 0.00) were associated with problematic coffee use. Conclusion: This study showed that one-third of the respondents had problematic coffee use. The starting point, duration, and amount of use had a strong association with problematic coffee use. Hence, focusing on addressing the mental health challenges associated with problematic/excessive coffee consumption among higher education students is advisable. Additionally, promoting awareness of problematic/excessive coffee use and its potential remedies is recommended.