A Sleep Hormone That Shields Your Muscles
Melatonin is best known as the hormone that tells your body it's time to sleep. But it has a second life that most people — including most athletes — don't know about. Beyond regulating your sleep-wake cycle, melatonin is a potent antioxidant and anti-inflammatory agent, capable of neutralizing the damaging molecules that accumulate in muscle tissue during intense exercise [1, 2].
A new systematic review and meta-analysis published in Frontiers in Nutrition — pooling data from 19 randomized controlled trials with 266 participants — set out to quantify whether these protective properties actually translate to real benefits for athletes [1]. The headline finding wasn't about sleep at all: melatonin significantly reduced creatine kinase (CK) levels, an enzyme released into the blood when muscle fibers are damaged, with remarkably consistent results across seven studies. In practical terms, this means less muscle breakdown from hard sessions — and potentially faster recovery between training days.
A similar protective trend was observed for another damage marker, lactate dehydrogenase (LDH), though this result had limited statistical significance. Notably, the muscle-protective effect was greater in competitive athletes than in recreational exercisers — a somewhat counterintuitive finding, since you might expect trained athletes to have more robust natural defenses. The authors suggest that training status may modulate how effectively exogenous melatonin supports the body's antioxidant systems.
This protection also appears to build over time. Multi-day supplementation protocols — taking melatonin over several consecutive evenings — were far more effective than single doses, with a fourfold difference in effect size. Rather than an acute shield, melatonin seems to work through cumulative antioxidant and anti-inflammatory protection that compounds across days. This makes it particularly relevant during training camps, heavy loading weeks, or congested competition schedules where the damage from one session hasn't fully cleared before the next one begins.
Endurance Aid, Not Race-Day Booster
Beyond muscle protection, the meta-analysis found a moderate improvement in endurance capacity — the ability to sustain prolonged effort. In particular, melatonin improved performance on time-to-exhaustion tests — protocols where you exercise at a fixed intensity until you can't continue. But it did not significantly improve time-trial performance, where you move a fixed distance. Time-to-exhaustion measures your tolerance for sustained hard effort, the kind of capacity that matters during training. Time-trials simulate race conditions. The paper's authors draw the conclusion explicitly: melatonin appears to be a training recovery aid, not a competitive performance enhancer.
This framing makes sense. If melatonin's primary benefit operates through reduced muscle damage and improved overnight recovery, you'd expect the payoff to show up in your ability to absorb training load — not in a single peak performance on competition day.
The picture was more mixed for other performance domains. Explosive power (vertical jumps, Wingate sprints) showed a small, statistically significant improvement, but the effect was modest enough that the researchers question whether it would matter in competition. Interestingly, adolescent athletes showed a stronger response than adults. Strength and speed showed no benefit at all. Melatonin did not improve sprint times, reaction time, handgrip strength, or squat performance. So if your training is built around maximal lifts or short sprints, melatonin isn't the supplement to reach for.
Evening vs. Daytime Intake
The meta-analysis confirmed that melatonin's benefits are strongly timing-dependent. Melatonin taken in the evening, with at least six hours before the next exercise session, consistently outperformed daytime dosing or pre-exercise intake. Evening dosing produced roughly double the endurance effect of daytime dosing, and for explosive power, intervals under two hours produced literally zero benefit.
The explanation is straightforward: melatonin is a sedative. Taken close to exercise it causes drowsiness — three of the 19 studies documented this directly. But taken at bedtime, those same sedative properties become an advantage: melatonin enhances sleep quality and supports overnight recovery processes. The next-day performance gains likely reflect this improved recovery between sessions rather than any direct effect during exercise.
Higher doses (6–10 mg) generally produced larger effects for endurance, while the common 5 mg dose showed essentially no endurance benefit in the subgroup analysis. For explosive power, the dose-response was less clear, so more isn't always better across all outcomes.
Who Should Consider It — and Who Shouldn't
The evidence points to a specific use case: endurance athletes during intensive training blocks. Training camps, back-to-back race weeks, heavy loading phases — situations where the limiting factor is how fast you recover between sessions, not how hard you can push in any single one. The optimal protocol appears to be 6–10 mg at bedtime over several consecutive days, with at least six hours before the next training session.
If your goals are strength, speed, or race-day performance, the evidence doesn't support melatonin supplementation. And regardless of your goals, morning or pre-exercise dosing is counterproductive — you'll get drowsiness without any upside.
Several limitations deserve a mention. The 19 trials had small sample sizes (10–30 participants each), and the vast majority studied male athletes — whether female athletes respond similarly is unknown. The studies were short-term, so whether these benefits compound into better long-term training adaptations remains an open question. And while the CK evidence is strong and consistent, some other biomarker findings are weaker and may be influenced by publication bias. Still, for athletes struggling with recovery during demanding training periods, melatonin does represent a low-risk, evidence-based option.
References
- Guo J, Zhou L, Gu J, Sun J, Liu G, Wei C. "Timing-Dependent Effects of Melatonin Supplementation on Exercise Performance and Exercise-Induced Muscle Damage: A Systematic Review and Meta-Analysis", Frontiers in Nutrition 13 (2026) 1742464. https://doi.org/10.3389/fnut.2026.1742464
- Reiter RJ, Mayo JC, Tan D, Sainz RM, Alatorre-Jimenez M, Qin L. "Melatonin as an Antioxidant: Under Promises but Over Delivers", Journal of Pineal Research 61 (2016) 253-278. https://doi.org/10.1111/jpi.12360