Acute caffeine supplementation as a nutrition-based strategy to mitigate sleep-loss-related cognitive and operational performance impairments in military personnel: a systematic review and meta-analysis.

BACKGROUND: Sleep loss is common in military operations and degrades vigilance, higher cognitive function, and operational performance. Whether acute caffeine meaningfully attenuates these decrements in military settings has not been quantitatively synthesized. METHODS: This study systematically searched PubMed, Web of Science, Cochrane Library, MEDLINE, Embase, and SPORTDiscus from database inception to the search cutoff date. Eligible studies were randomized controlled or crossover trials that included military personnel or military-related populations, administered caffeine under conditions of sleep deprivation, sleep restriction, or sustained wakefulness, and compared caffeine with placebo or a non-caffeinated control. The primary outcomes were categorized as vigilance and response performance, complex cognitive performance, and military task performance. Risk of bias was assessed using the RoB 2 tool, and meta-analyses were conducted using StataMP 17.0. RESULTS: Seven randomized, double-blind, placebo-controlled studies were included. The meta-analysis showed that, compared with placebo, caffeine significantly improved vigilance and response performance under conditions of sleep deprivation or sleep restriction (SMD = 0.73, 95% CI: 0.50-0.96, I2 = 0.0%), complex cognitive performance (SMD = 0.54, 95% CI: 0.16-0.93, I2 = 0.0%), and military task performance (SMD = 0.45, 95% CI: 0.19-0.71, I2 = 29.2%). Overall, the ergogenic effects of caffeine were most consistent for vigilance and response performance, showed stable beneficial effects on complex cognitive performance, and were primarily reflected in improved task-execution speed and operational efficiency for military task performance. CONCLUSION: The available evidence suggests that acute caffeine supplementation improves vigilance and response performance during sleep loss in military personnel, with additional benefits for complex cognitive and military task performance. Effects were most consistent for vigilance and response speed, whereas benefits for complex cognition and military task performance were more task-dependent. These findings support caffeine as a practical short-term adjunct to fatigue management during military operations involving sleep loss, although further studies are needed to refine dose, timing, and task-specific use. SYSTEMATIC REVIEW REGISTRATION: https://www.crd.york.ac.uk/PROSPERO/view/CRD420261375742, identifier CRD420261375742.