Caffeine in sport: possible benefits, doses and risks

What caffeine can and cannot do in endurance sport, how to start low, count every source and protect sleep and health.

Roasted coffee beans as a source of caffeine
Roasted coffee beans as a source of caffeine

Caffeine can reduce perceived effort and improve endurance performance for some athletes, but the effect is not guaranteed. Habit, dose, anxiety, sleep, genetics and event time all influence the response.

More is not automatically better. Start low, test during training and count coffee, gels, drinks and capsules together.

Key points

Start near 1–3 mg/kg rather than with a large dose.
Test at race intensity and the same time of day as the event.
For a late start, lost sleep may outweigh a small performance benefit.

What controlled trials show

In controlled cycling and running studies, caffeine extended time to exhaustion or improved a distance trial in some groups. Most experiments are small, protocols differ and other studies find no benefit, so a percentage from one trial cannot be promised to everyone.

Caffeine does not create glycogen and cannot replace training or fuelling. Its main effects involve the central nervous system and perceived effort.

Dose and timing

A practical starting dose is 1–3 mg/kg around 45–60 minutes before the key effort. For a 70 kg athlete that is 70–210 mg. Some respond to less; larger doses more often cause anxiety, palpitations and gastrointestinal discomfort.

A late-race caffeinated gel still works gradually. Read labels carefully: two gels, coffee and an energy drink can add up without being noticed.

Isostar bottle and energy product beside a training route
Isostar bottle and energy product beside a training route

Sleep and adverse effects

In a controlled sleep trial, 400 mg caffeine impaired sleep even when taken six hours before bed. Sports doses may be lower, but evening use can still compromise recovery. A non-caffeinated option may be smarter for a late event.

Stop if marked tremor, anxiety, dizziness, chest pain or irregular heartbeat occurs; severe symptoms require medical help.

A safe test protocol

  1. Record habitual daily caffeine.
  2. Choose a low dose and familiar product.
  3. Test in a controlled race-pace session.
  4. Assess performance, stomach, heart rate, anxiety and that night’s sleep.
  5. If there is no benefit, a larger dose is not mandatory.

Seek medical advice in pregnancy, heart rhythm disorders, uncontrolled blood pressure, anxiety disorders, medication use or for minors.

Keep a caffeine log

Write the exact time and milligrams from every source rather than “two coffees”. Add body mass, session start, food, perceived effort and time to fall asleep. Repeat the same protocol at least twice.

An improved session with worse sleep is not automatically a successful experiment. During a multi-day event or hard training block, next-day recovery may matter more than a small immediate gain. Choose the lowest dose with a clear benefit and no meaningful adverse effect.

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Frequently asked questions

Does coffee work like a caffeinated gel?

Both may supply caffeine, but coffee dose varies and a gel also contains carbohydrate. Compare the label and tolerance.

Must I stop coffee before a race?

Not necessarily. Evidence for required withdrawal is mixed; do not introduce a new withdrawal routine during race week.

Does caffeine dehydrate athletes?

Typical sports doses do not make a drink useless for hydration, but caffeine is not a replacement for an individual fluid plan.

Related guides

Sources and editorial approach

  1. Bell and McLellan (2002), caffeine and cycling endurance trial
  2. Bridge and Jones (2006), caffeine and 8 km running trial
  3. Drake et al. (2013), caffeine timing and sleep trial

Official Isostar / Nutrition & Santé image used by INTERVALS under its distribution agreement.

Author: INTERVALS editorial team. This content was localised and expanded for Baltic athletes from authorised Isostar / Nutrition & Santé material. Scientific claims were checked against the cited primary sources. Last reviewed: 21 August 2026.
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