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Caf9.5
Caffeine Research
Likely helpsModerate safety
146 peer-reviewed studies
What the evidence says
Likely helps
Caffeine appears to help in 22 of 25 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 2008–2026 with a typical study size of 71 participants.
Based on 146 studies · 26 meta-analyses · 52 RCTs · 142,640 total participants
Confidence
High
What the studies found
22helped3unclear· 121 more without graded effect data
By outcome
Cognitive functionEnhances short-term memory consolidation and recall · 30-60 minutes
Weight managementAcute thermogenic and lipolytic effect · 30-60 minutes
Mostly mechanism / observational12 studies
Sleep & insomnia
Likely helps10 studies
Therapeutic & clinical
Probably helps8 studies
Safety profile
Mostly mechanism / observational8 studies
Focus & attentionImproved attention, concentration, and reaction time · 30-60 minutes
Mostly mechanism / observational5 studies
Migraine & headache
Mostly mechanism / observational5 studies
By the numbers
Pulled from 62 studies with measurable effects
Likely real effects
70%
across studies
People studied
143k
typical study: 71 people
Strongest designs
78
26 pooled, 52 randomised
Showed benefit
88%
22/25 studies
How long studies ran
1–4 weeks
1
Populations Studied
General population10
Athletes4
Adults3
Young adults2
Active research area
132 studies in the last 5 years · Latest meta-analysis: 2026
200820172026
1IBD riskMeta-Analysisn=209 · medium study2026
The relationship between caffeine intake and IBD risk varies by region, age, caffeine source, smoking, and education level.
Wu X et al. · Journal of gastroenterology and hepatology (2026)
No clear effect
← WorseNo effectBetter →
The meta-analysis showed no significant association between caffeine intake and IBD (RR = 0.84, 95% CI = 0.68-1.04).
In Americans, caffeine increased UC risk by 68% (RR = 1.68, 95% CI = 1.17-2.42).
Age analysis showed caffeine increased IBD risk by 4.52 times in those ≤18 (RR = 4.52, 95% CI = 1.59-12.88) but decreased risk by 7% in those >18 (RR = 0.93, 95% CI = 0.73-1.18).
2Fat oxidation rate during exerciseMeta-AnalysisCited 36×n=2,020 · very large study2020
However, the fitness level of the participant may modulate the magnitude of the effect of caffeine on fat oxidation during exercise.
Collado-Mateo D et al. · Nutrients (2020)
Large benefit
← WorseNo effectBetter →
Likely real
A subsequent meta-analysis was performed using the random effects model to calculate the standardized mean difference (SMD).
The meta-analysis revealed that caffeine significantly (p = 0.008) increased the fat oxidation rate (SMD = 0.73; 95% CI = 0.19 to 1.27).
This increment was consistent with a significant (p = 0.04) reduction of the respiratory exchange ratio (SMD = -0.33; 95% CI = -0.65 to -0.01) and a significant (p = 0.049) increase in the oxygen uptake (SMD = 0.23; 95% CI = 0.01 to 0.44).
5Exercise performance in time trialsMeta-AnalysisCited 4×n=95 · small study2024
CAF+nitrates did not offer further benefits on exercise performance or physiological variables from the isolated intake of CAF and nitrates.
Gilsanz L et al. · Nutrients (2024)
No clear effect
← WorseNo effectBetter →
Could be chance
The meta-analysis revealed that caffeine and nitrates supplementation (CAF+nitrates) did not enhance performance in time trials (TTs) over the CAF alone (g = -0.06; 95% CI = -0.46 to 0.35; p = 0.78) or nitrates alone (g = 0.29; 95% CI = -0.12 to 0.70; p = 0.17).
CAF+nitrates did not affect heart rate during submaximal exercise trials over CAF alone (g = 0.04; 95% CI = -0.31 to 0.40; p = 0.80) or nitrates alone (g = -0.15; 95% CI = -0.50 to 0.20; p = 0.40).
Likewise, CAF+nitrates did not affect oxygen uptake during submaximal exercise trials over CAF alone (g = -0.04; 95% CI = -0.45 to 0.37; p = 0.84) or nitrates alone (g = -0.29; 95% CI = -0.70 to 0.12; p = 0.16).
7Time to exhaustion in running testsMeta-AnalysisCited 40×n=254 · medium study2022
More evidence is needed to establish the ergogenic effect of caffeine on endurance running in women or the best dose to maximize the ergogenic benefits of caffeine supplementation.
Wang Z et al. · Nutrients (2022)
Noticeable benefit
← WorseNo effectBetter →
Likely real
A subsequent meta-analysis was performed using the random effects model to calculate the standardized mean difference (SMD) estimated by Hedges’ g and 95% confidence intervals (CI).
The meta-analysis revealed that the time to exhaustion in running tests was improved with caffeine (g = 0.392; 95% CI = 0.214 to 0.571; p < 0.001, magnitude = medium).
Subgroup analysis revealed that caffeine was ergogenic for time to exhaustion trials in both recreational runners (g = 0.469; 95% CI = 0.185 to 0.754; p = 0.001, magnitude = medium) and trained runners (g = 0.344; 95% CI = 0.122 to 0.566; p = 0.002, magnitude = medium).
9Association between sleep habits and substance useMeta-AnalysisCited 32×n=46 · small study2023
Longitudinal results were inconclusive.
Meneo D et al. · Sleep medicine reviews (2023)
Longitudinal results were inconclusive.
We found a distinct pattern of associations between different substances and different sleep outcomes.
Further investigation considering the multidimensionality of sleep would create a better understanding of the complex relationship between substance use and sleep health in young adults.
10Panic attacks in panic disorder patientsMeta-AnalysisCited 40×n=237 · medium study2022
The results confirm that caffeine at doses roughly equivalent to 5 cups of coffee induces panic attacks in a large proportion of PD patients and highly discriminates this population from healthy adults.
Klevebrant L et al. · General hospital psychiatry (2022)
Huge benefit
← WorseNo effectBetter →
The 9 studies investigating panic attacks included 237 patients, of which 51.1% had a panic attack following caffeine, but none after placebo.
Six of these studies compared 128 patients with 115 healthy controls (HC), finding that patients (53.9%) were more vulnerable than HC (1.7%) for panic attacks following caffeine (log RR: 3.47; 95% CI 2.06-4.87).
Six studies investigated subjective anxiety in 121 patients and 111 HC following caffeine, with an overall effect indicating increased sensitivity to the anxiogenic effects of caffeine in the patient group (Hedges' g = 1.02 [95% CI: 0.09-1.96]).
The current evidence suggests no significant relationship between caffeine intake and ED, but limited studies limit conclusions.
Karimi M et al. · Journal of health, population, and nutrition (2024)
No clear effect
← WorseNo effectBetter →
Could be chance
The results indicate that there was no significant relationship between coffee consumption and the risk of ED (relative risk [RR] = 0.94, 95% CI: 0.86-1.03; p = 0.999).
The current evidence suggests no significant relationship between caffeine intake and ED, but limited studies limit conclusions.
Future research should focus on larger sample sizes, standardized outcome assessments, and different dosages and forms of caffeine consumption.
12Total sleep timeMeta-AnalysisCited 126×n=24 · very small study2023
Caffeine consumption reduced total sleep time by 45 min and sleep efficiency by 7%, with an increase in sleep onset latency of 9 min and wake after sleep onset of 12 min.
Gardiner C et al. · Sleep medicine reviews (2023)
Noticeable benefit
← WorseNo effectBetter →
Caffeine consumption reduced total sleep time by 45 min and sleep efficiency by 7%, with an increase in sleep onset latency of 9 min and wake after sleep onset of 12 min.
Duration (+6.1 min) and proportion (+1.7%) of light sleep (N1) increased with caffeine intake and the duration (-11.4 min) and proportion (-1.4%) of deep sleep (N3 and N4) decreased with caffeine intake.
To avoid reductions in total sleep time, coffee (107 mg per 250 mL) should be consumed at least 8.8 h prior to bedtime and a standard serve of pre-workout supplement (217.5 mg) should be consumed at least 13.2 h prior to bedtime.
13Physical performance in female athletesMeta-AnalysisCited 19×2022
More studies are needed in female athletes that measure the effects of different EAs on sports performance, such as beetroot juice, beta-alanine or sodium phosphate, as the studies to date are scarce and there are many types of EA that need to be further considered in this population, such as creatine and taurine.
López-Torres O et al. · Nutrients (2022)
A random-effects model and the standardized mean differences (SMD) ± 95% confidence intervals (CI) were reported.
Aerobic tests could be improved with the use of taurine, caffeine, and beta-alanine.
No conclusive effects of beetroot juice, polyphenols, or creatine in improving aerobic performance were shown.
14Physical performance with caffeinated drinksSystematic ReviewCited 25×2021
Overall, the current systematic review provides evidence of the efficacy of caffeinated drinks as a valid form for caffeine supplementation in sport.
Jiménez SL et al. · Nutrients (2021)
Due to their composition, caffeinated sports drinks seem to be more beneficial to consume during long-duration exercise, when the drinks are used for both rehydration and caffeine supplementation.
Energy drinks may be more appropriate for providing caffeine before exercise.
Lastly, the magnitude of the ergogenic benefits obtained with caffeinated drinks seems similar in women and men athletes.
15Pupillary parametersMeta-AnalysisCited 3×n=14 · very small study2024
This meta-analysis examined the effects of Caffeine.
Hartmann EV et al. · Behavioral and brain functions : BBF (2024)
We summarize the numeric results as both differences in absolute pupil diameter and in terms of effect sizes.
The evidence available in the literature does not provide consistent results but studies rated as valid by quality assessment suggest a small effect of caffeine on pupil parameters.
More studies are needed using modern pupil assessment methods, robust study design, and caffeine dose-response methodology.
17Muscle strength and powerMeta-AnalysisCited 228×2018
The meta-analyses showed significant ergogenic effects of caffeine ingestion on maximal muscle strength of upper body and muscle power.
Grgic J et al. · Journal of the International Society of Sports Nutrition (2018)
Noticeable benefit
← WorseNo effectBetter →
Likely real
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).
The meta-analyses showed significant ergogenic effects of caffeine ingestion on maximal muscle strength of upper body and muscle power.
In hypertensive individuals, caffeine intake produces an acute increase in BP for ≥3 h.
Mesas AE et al. · The American journal of clinical nutrition (2011)
In 5 trials, the administration of 200-300 mg caffeine produced a mean increase of 8.1 mm Hg (95% CI: 5.7, 10.6 mm Hg) in systolic BP and of 5.7 mm Hg (95% CI: 4.1, 7.4 mm Hg) in diastolic BP.
In hypertensive individuals, caffeine intake produces an acute increase in BP for ≥3 h.
However, current evidence does not support an association between longer-term coffee consumption and increased BP or between habitual coffee consumption and an increased risk of CVD in hypertensive subjects.
19Exercise performanceMeta-AnalysisCited 243×n=21 · very small study2020
Synthesis of the currently available meta-analyses suggest that caffeine ingestion improves exercise performance in a broad range of exercise tasks.
Grgic J et al. · British journal of sports medicine (2020)
However, not all analyses provided a definite direction for the effect of caffeine when considering the 95% prediction interval.
Synthesis of the currently available meta-analyses suggest that caffeine ingestion improves exercise performance in a broad range of exercise tasks.
Ergogenic effects of caffeine on muscle endurance, muscle strength, anaerobic power and aerobic endurance were substantiated by moderate quality of evidence coming from moderate-to-high quality systematic reviews.
Given the spectrum of conditions studied and the robustness of many of the results, these findings indicate that coffee can be part of a healthful diet.
Grosso G et al. · Annual review of nutrition (2017)
Of the 59 unique outcomes examined in the selected 112 meta-analyses of observational studies, coffee was associated with a probable decreased risk of breast, colorectal, colon, endometrial, and prostate cancers; cardiovascular disease and mortality; Parkinson's disease; and type-2 diabetes.
Of the 12 unique acute outcomes examined in the selected 9 meta-analyses of RCTs, coffee was associated with a rise in serum lipids, but this result was affected by significant heterogeneity, and caffeine was associated with a rise in blood pressure.
Given the spectrum of conditions studied and the robustness of many of the results, these findings indicate that coffee can be part of a healthful diet.