Israel Medical Association Journal

Operational forces increasingly face concurrent sleep restrictions and thermal strain, yet mission planning lacks field-relevant guidance on their combined cognitive effects and management. This critical narrative review synthesizes laboratory, field, and military-relevant evidence on how sleep loss and heat stress affect sustained attention, drowsiness, reaction time, executive control, and feedback-guided decision making. Sleep deprivation produces dose-responsive vigilance instability across total sleep deprivation and chronic partial restriction, with lapses and response-time variability providing sensitive monitoring endpoints. Heat stress produces task-dependent cognitive costs. Simple reaction time may remain relatively preserved during modest strain, whereas executive control, working memory, inhibition, and cognitive flexibility appear more vulnerable as physiological reserve narrows, particularly during dehydration, exertion, and protective equipment use.

Military multistressor studies show broad cognitive deterioration when sleep restriction co-occurs with heat, dehydration, undernutrition, and sustained workload. However, bundled designs cannot determine whether sleep and heat act additively, synergistically, or through threshold-dependent interactions. Key gaps include factorial sleep × heat trials, standardized cognitive batteries, mechanistic telemetry, and prospective modeling of moderators such as trait-like sleep-loss vulnerability, baseline sleep debt, chronotype, heat acclimation, hydration practices, protective-equipment burden, and sex. Commanders and medical planners should treat concurrent sleep restriction and thermal strain as a compounded operational risk state and apply layered controls, including protected sleep, scheduling, cooling, hydration, work-rest cycles, objective vigilance screening, task rotation, and supervisory cross-checks for high-consequence decisions.

Objectives: To assess whether a new herbal-based potentially wake-promoting beverage is effective in counteracting somnolence and reduced post-lunch performance.

Methods: Thirty healthy volunteers were studied on three different days at the sleep clinic. On each visit they ate a standard lunch at noontime, followed by a drink of "Wake up®," 50 mg caffeine, or a placebo in a cross-over double-blind regimen. At 30 and 120 minutes post-drinking, they underwent a battery of tests to determine the effects of the beverage. These included: a) a subjective assessment of alertness and performance based on a visual analog scale, and b) objective function tests: the immediate word recall test, the digit symbol substitution test (DSST), and hemodynamic measurements. The results of the three visits were compared using one-way analysis of variance, with P < 0.05 considered statistically significant.

Results: In all performance tests, subjective vigilance and effectiveness assessment, both Wake up® and caffeine were significantly superior to placebo 30 minutes after lunch. However, at 2 hours after lunch, performance had deteriorated in those who drank the caffeine-containing drink, while Wake up® was superior to both caffeine and placebo. Blood pressure and pulse were higher 2 hours after caffeine ingestion, compared to both Wake up® and placebo.

Conclusions: These results suggest that a single dose of Wake up® is effective in counteracting the somnolence and reduced performance during the post-lunch hours. In the current study it had no adverse hemodynamic consequences.