Razi Journal of Medical Sciences

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Background & Aims: Athletes are always looking for a way to improve their performance(1). Caffeine is one of the most common supplements which may increase mental and physical performance and acts as an ergogenic aid especially in repeated running (2-3). It has been shown that acute caffeine supplementation may affect endothelium and vascular smooth muscles which may be due to: caffeine acts as adenosine receptors antagonist, phosphodiesterase inhibition, increase in intracellular calcium concentration, nitric oxide synthase enzyme gene expression (4). At resting individuals, caffeine consumption can increasing intracellular calcium concentration, leading to nitric oxide synthase (NOS) enzyme gene expression which stimulates nitric oxide (NO) production. Increase in NO level will ultimately cause vascular smooth muscles relaxation and vasodilation.(5-6)caffeine supplementation an hour before aerobic exercise, could reduce extracellular fluid and blood flow, despite it has showed beneficial effects for increased demand during exercise (7-10). Caffeine may increase systolic and diastolic blood pressure (11). Beetroot-juice is an antioxidant and nitric oxide source which may have anti-inflammatory effect against free radicals and beneficial effects for cardiovascular system and lead to better physical performance (12-18) nitrate consumption can produce nitric oxide from L-arginine amino acid and improve performance (19-20). Nitrate supplementation can increase nitric oxide level In in plasma and decrease blood pressure (21). Nitric oxide may regulate vasodilatory factors and vascular tone (22). Studies have suggested that nitrate supplementation may increase vasodilation in active tissues and increase vasoconstriction in inactive tissues via increasing endothelin-1 level (23), moreover, it has been suggested that Beetroot-juice supplement may decrease blood pressure and improve performance related factors (24). The purpose of this study was to evaluate the effect of acute caffeine supplementation along with beetroot-juice on vasodilatory factors and physical performance in athletes.
Methods: In this study, ten high performance runners were divided into three experimental trials as high dosage,low dosage supplementation and placebo. Participants drink the supplementations with 250 ml water two times per day during seven days before 5000 meter endurance performance. Rest heart rate, blood pressure, endothelin-1, collagen-18 and nitric oxide level were measured. Participants for this study were 18-30 years old male runners with at least 2 years of running experience which were randomly divided into the following 3 groups after introduction session. At the first day of experiment, participants were present fasted for (8-10 hours) and inactivity status for at least 48 hours. Heart rate and blood pressure were measured with digital pulse meter and rosmax sphygmomanometer. Blood samples were collected from antecubital vein. After 5 minutes warm up, participant started 5 km running.
Participants were randomly divided in to three supplementation groups as following:
1. 9.6 mmol Beetroot-juice and 400 mg caffeine
2. 4.8 mmol Beetroot-juice and 200 mg caffeine
3. Placebo (PLB) group
physical activity was considered as 5 km running tests. At the first day, heart rate and blood pressure were assessed before the running test. Venous blood samples were collected to assess vasodilatory factors including: coll-18, ET-1, NO and nitrite. Participants start the running test after 5 minutes warmup and at the end of the test, all the measurements were repeated. At the second day, participants completed 1500 running test after 5 minutes warm up and consumed supplement. From the third day until day 6, supplementation was continued and participant were fellow up via calls. At the seventh day, heart rate and blood pressure were measured, participants consume supplements according to their group tags 60 minutes prior to their running test, and completed 5 km test after 5 minutes warm up. At day eight, participants consumed supplements and completed 1500 running test. Wash out phase was started from day 9 to 14 and participants did not consume any supplements for a week.
In this study, regression analysis with repeated measurements with generalized estimation equation approach.
Results: The results from the study showed no significant difference for endothelin-1 between the 3 groups before and after the intervention which means that Beetroot-juice  combined with caffeine supplementation had no effect on serum endothelin-1 level (p=0.52).
The results from statistical analysis showed no significant difference between the groups for collagen-18 which means supplementation was not effective on collagen-18 level (p=0.87).
The results suggest that supplementation could not affect NO level significantly (p=0.97) but physical activity increased NO level by 90.58 units (p=0.001). Systolic bp was not affected by the supplementation dosage (p=0.17). supplementation did not affect systolic BP significantly (p=0.09). systolic BP was affected by physical activity and systolic BP was increased by 2.58 mmHg. Supplementation dosage did not make any significant difference in experimental groups (p=0.28). Supplementation did not have any significant change in heart rate (p=0.25), despite physical activity effect (p=0.001) there was an increase in heart rate within 1500 meter running in comparison with start moment (p=0.001).
Conclusion: This study suggests that the combination of caffeine and Beetroot-juice  supplementation may not have beneficial effects of vasodilatory factors and physical performance in elite male runners which may be due to NO effect reduction when consumed in combination with caffeine while exercise may influence vasodilatory and performance parameters.

Keywords: Beetroot-juice, Caffeine, Vasodilation, Performance, Elite athlete

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