Randomized double-blind placebo-controlled crossover study of caffeine in patients with intermittent claudication

Background: Intermittent claudication is a disabling symptom of peripheral arterial disease for which few medical treatments are available. This study investigated the effect of caffeine on physical capacity in patients with intermittent claudication. Methods: This randomized double-blind placebo-controlled crossover study included 88 patients recruited by surgeons from outpatient clinics. The participants abstained from caffeine for 48 h before each test and then received either a placebo or oral caffeine (6 mg/kg). After 75 min, pain-free and maximal walking distance on a treadmill, perceived pain, reaction times, postural stability, maximal isometric knee extension strength, submaximal knee extension endurance and cognitive function were measured. The analysis was by intention to treat. Results: Caffeine increased the pain-free walking distance by 20.0 (95 per cent confidence interval 3.7 to 38.8) per cent (P = 0.014), maximal walking distance by 26.6 (12.1 to 43.0) per cent (P < 0.001), muscle strength by 9.8 (3.0 to 17.0) per cent (P = 0.005) and endurance by 21.4 (1.2 to 45.7) per cent (P = 0.004). However, postural stability was reduced significantly, by 22.1 (11.7 to 33.4) per cent with eyes open (P < 0.001) and by 21.8 (7.6 to 37.8) per cent with eyes closed (P = 0.002). Neither reaction time nor cognition was affected. Conclusion: In patients with moderate intermittent claudication, caffeine increased walking distance, maximal strength and endurance, but affected balance adversely. Registration number: NCT00388128 (http://www.clinicaltrials.gov).