Exercise, not caffeine, drove hematological changes during a 17-min CrossFit workout, and acute caffeine at 6 and 9 mg/kg body mass selectively raised post-exercise glucose, while hematological variables and most biochemical markers (including serum minerals) were unaffected.
Acute caffeine ingestion (3, 6, or 9 mg/kg BM) did not modulate blood cell indices during the CrossFit workout; exercise was the predominant driver of hematological changes.
Glucose was the only variable with a significant treatment × time point interaction.
Medium (6 mg/kg BM) and high (9 mg/kg BM) caffeine doses produced significantly greater post-exercise glucose elevations than baseline and placebo visits.
Phosphate concentrations increased over time, particularly post-exercise, and no treatment effect remained after excluding the baseline visit in a sensitivity analysis.
Calcium dynamics were influenced by temporal factors rather than caffeine, and magnesium concentration remained stable.
Overall, hematological variables and most biochemical markers were unaffected by acute caffeine during the CrossFit workout.
This study tested whether caffeine changes blood measures in people doing a hard, short CrossFit workout. Twenty-six moderately trained CrossFit athletes took caffeine at three doses (3, 6, or 9 mg per kg of body mass) or a placebo 70 minutes before a 17-minute workout. Neither the athletes nor the researchers knew which was given, and each athlete tried all conditions. The workout itself changed many blood measures, but caffeine did not alter blood cell counts or indices. Minerals such as calcium, phosphate, and magnesium shifted mainly with time and exercise, or stayed stable, rather than because of caffeine. The one clear caffeine effect was on blood glucose: the 6 and 9 mg/kg doses led to higher glucose after exercise than placebo or baseline. This research suggests that caffeine at these doses has limited effects on most blood markers during intense exercise, but that moderate-to-high doses can raise post-exercise glucose. The sample was small and consisted of trained athletes, so the findings may not apply to everyone.
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Upload Your LabsGłówka N, Podgórski T, Malik J, Nowaczyk P, Durkalec-Michalski K. (2026). Hematological and biochemical responses to three doses of caffeine during the CrossFit® workout: a randomized, double-blind, crossover trial.. Journal of the International Society of Sports Nutrition. https://doi.org/10.1080/15502783.2026.2740805