Morning coffee worsens exercise-induced haemostatic responses in sedentary men

Drinking coffee in the morning appears to heighten the risk of stroke and cardiac events in people who exercise early. Findings from a recent study suggest that morning exercise causes a greater prothrombotic status than evening exercise, and this effect intensifies with acute caffeine intake.

Thirty caffeine-naïve sedentary men participated in this randomized, double-blind, placebo-controlled crossover study. Each of them performed four combined exercise sessions (two at 7 AM and two at 6 PM) following consumption of caffeine or placebo. The authors collected blood samples pre-, postexercise, and after 60 min of recovery.

Exercise triggered increases in platelet aggregation, thrombin generation, tPA activity, and clot lysis time across all conditions. No change was observed in plasminogen activator inhibitor-1 (PAI-1) activity postexercise, but it declined during recovery.

Notably, caffeine exacerbated the exercise-induced increase in platelet aggregation, thrombin generation, and clot lysis time, especially in the morning, with no significant changes in tPA or PAI-1 activity. By contrast, platelet aggregation, thrombin generation, PAI-1 activity, and clot lysis time were lower, and tPA activity was higher, in the evening.

“The enhanced fibrinolytic capacity in the evening may create a more favourable haemostatic setting for exercise and cardiovascular safety, a hypothesis that warrants confirmation with denser sampling protocols,” the authors said.

“Caffeine, a performance-enhancing substance, affects haemostasis,” they said.