New study📅 25.05.2026🤖 AI Research

Caffeine and Endurance: Even 1.3–3 mg/kg Improves Time-Trial Performance (n=716, 48 RCTs)

A Brazilian team has updated the picture for the world's most popular sports supplement. A new systematic review of 48 randomized, placebo-controlled trials shows you do not need to load up on 6 mg/kg of caffeine — even a small cup of espresso 30 to 60 minutes before a run measurably improves performance. Moderate doses of 4 to 6 mg/kg, however, deliver a noticeably more consistent effect.

What was studied

The Brazilian research group pooled all randomized controlled trials that compared a single dose of anhydrous caffeine versus placebo in adults performing aerobic exercise under a time-trial protocol (running, cycling, swimming, rowing).

48 studies were included, with a total of 716 participants. Doses were split into three categories:

• Low: ≤3 mg/kg (for a 70 kg person, about 210 mg — one strong cup of coffee)
• Moderate: 4–6 mg/kg (for 70 kg, 280–420 mg)
• High: >6 mg/kg (for 70 kg, 420+ mg — two large cups or a dedicated capsule)

The authors used a random-effects model because of substantial between-study heterogeneity, and assessed risk of bias using the Cochrane RoB tool.

The main result

Both low and moderate doses significantly reduced time-trial completion time versus placebo. The standardized mean difference (SMD) is the effect size — a negative value means "time decreased":

For context: an SMD of 0.2 is considered a small effect, 0.5 moderate, and 0.8 large. So moving from placebo to a moderate dose of caffeine gives what statisticians call a "moderate" boost — which on a 10K race translates to tens of seconds for a recreational runner.

What this means for you

If you are a recreational athlete rather than a professional, the practical takeaways are:

1. You do not need megadoses. One strong cup of coffee (≈100–150 mg) or a double espresso (≈150–200 mg) 30 to 60 minutes before training already provides a measurable endurance advantage.
2. A moderate dose works more reliably. If you are preparing for a race or a key training session, 4–6 mg/kg (280–420 mg for a 70 kg person) gives a better effect-to-predictability ratio.
3. "More" does not mean "better." Doses above 6 mg/kg provide no additional performance benefit but raise the chance of tachycardia, GI upset, tremor, and sleep disruption.
4. Tolerance. The authors did not run a subgroup analysis comparing habitual coffee drinkers versus non-consumers. If you drink three or more cups daily, the effect is likely smaller — other literature suggests as much.

One important nuance: calculate your dose by body weight, not by eye. 200 mg for a 60 kg person is 3.3 mg/kg (the low end of moderate), but for a 90 kg person it is only 2.2 mg/kg (still in the low range). A useful hack: check the label on coffee capsules or pre-workout gels.

Important caveats

Several limitations the authors explicitly note:

• High heterogeneity — different sports (running, cycling, swimming), different distances, different training levels.
• Only aerobic time-trials. Strength work, sprints, and team sports were not included — caffeine's effect on those has been studied separately.
• Per-study sample sizes are often small — typically a median of 10–15 participants.
• This is a preprint that has not yet passed full peer review.
• Individual variability: roughly 30–40% of people are "non-responders" due to the CYP1A2 polymorphism, with a weaker or absent effect.