Caffeine may buy athletes performance and charge it to their sleep

Caffeine is one of the most widely used aids in sport because it may enhance athletic performance. But performance is only half of the equation: adaptation happens in recovery, and sleep is the deepest form of recovery an athlete has. If the same substance that lifts a session also disturbs the night that follows, athletes could be quietly trading long-term gains for short-term output. This review set out to establish what randomised trials actually show about caffeine's effects on sleep in the athletic population specifically.

The reviewers registered their protocol on PROSPERO and systematically searched seven databases, including PubMed/MEDLINE, Embase, Scopus and Web of Science, for randomised controlled trials published between 1980 and December 2023. From 1469 records, nine trials in professional athletes met the eligibility criteria. The trials between them assessed a wide range of sleep parameters, including duration, quality, efficiency, number of awakenings and sleep onset latency. Both objective and subjective methods of measuring sleep were included in the review.

The nine trials did not tell a single story: results varied across sleep quality, quantity, efficiency, awakenings and how long it took athletes to fall asleep. The reviewers suggest these differences may come down to when caffeine was taken relative to bedtime and to exercise, how habituated each athlete was, and the dose prescribed. Given the nature of caffeine, they conclude that insomnia following ingestion is likely. Their overall verdict is that while caffeine supplementation may enhance athletic performance, it could have a detrimental effect on sleep and therefore on recovery.

Caffeine's place as a performance aid is well established in sports nutrition, but its downstream cost to sleep has had far less systematic attention, and this review gathers the trial evidence in athletes for the first time in this form. That only nine trials qualified shows how thin the evidence base still is. The inconsistency between trials means the field cannot yet say what dose, at what time, harms which athletes. The reviewers call for supplementation to account for individual responses so that performance gains do not come at sleep's expense.

If you use caffeine around training, the honest reading is that its effect on your sleep is personal: timing, dose and how accustomed you are all appear to matter. Someone who trains and takes caffeine early in the day has less to think about than someone hitting an evening session on a strong pre-workout. There is no single number here to act on, but the direction of concern is clear enough to be worth noticing on nights when sleep goes badly after a caffeinated session.