Research code: 12402159
Ethics code: IR.IAU.SRB.REC.1399.005
Clinical trials code: IRCT20200707048041N1

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Science and Research Branch,Islami Azad University ,
Abstract:   (206 Views)
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, nitrate and cardiovascular function:
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.
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.
Physical assessment before intervention:
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.
Supplementation protocol:
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 exercise protocol:
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.
Statistical analysis:
In this study, regression analysis with repeated measurements with generalized estimation equation approach.
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).
Nitric oxide level:
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:
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).
Heart rate:
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).
The results from this study have indicated that acute caffeine combined with Beet juic did not change vascular factors significantly in runners. Furthermore, the results suggest no significant alternation in systolic, diastolic blood pressure and heart rate.
Caffeine in assumed as ergogenic supplement which is available in several forms including powder, capsules or tablets (25-26). Caffeine can stimulate central nervous system due to inhibitory effect on adenosine, increasing catecholamines and calcium release, also caffeine supplementation effects for 3-6 mg/kg on cardio-vascular system have been shown in several studies (27). Beetroot-juice is a nitrate donor and increase in its level may reduce systolic blood pressure, increase muscular oxygenation and decrease oxygen consumption cost. According to American Heart Association, beetroot-juice may act via a dose-dependent mechanism in systolic and diastolic blood pressure reduction and may have the maximum effect 2-3 hours after consumption(28).  NO production during physical activity, mainly from endothelial cells, leads to vasodilation and vascular stability (29). Acute nitrate supplementation may improve both central and peripheral vascular endothelium function (30). Nitrate consumption can increase nitrite level which is NO precursor (25) and may lead to better endurance performance, endothelial function improvement and reduction in blood pressure (26). In the other words, nitrate consumption may play a vaso-protective role and decrease endothelial dysfunction and platelets aggregation induced by collagen and adenosine diphosphate (ADP), especially 2.5 hour after consumption (31). Beetroot-juice is a source of nitrate and has gain attention among athletes especially endurance athletes. It is suggested that acute or chronic 8 mmol nitrate consumption increased performance (21). It is assumed that nitrate level may affect endothelium function and decrease in NO level may lead to endothelium dysfunction. Endothelium can regulate vascular tone via releasing substances including endothelin which play systemic effects on vascular function and remodeling (32).Studies have shown a J-curve-type or U-curve-type relation between caffeine and cardiovascular system. It seems that caffeine consumption may improve endothelial function through increasing nitric oxide bioavailability, but the results from studies has remained controversial (4). Increase in intracellular calcium concentration may enhance nitric oxide production via increasing nitric oxide synthase enzyme gene expression which may help vasodilation. Moreover, caffeine is an adenosine receptor antagonist which is a vasoconstriction factor (27). The effect of caffeine consumption on systolic and diastolic blood pressure assessment suggested no significant difference before and after caffeine and physical activity consumption (28).  Assessments on caffeine consumption effects on endothelial function and blood pressure, have indicated that caffeine consumption can cause significant improvement for endothelial function, despite it did not affect blood pressure and dilation induced blood flow significantly (33). The mechanism which caffeine may improve endothelial function, may be due to increase in NO bioavailability (34). 80 mg of caffeine consumption, may increase platelets aggregation induced by ADP, 60 minutes after ingestion (35). Studies on heart rate changes followed by caffeine ingestion, demonstrated contra verse results, as heart rate may increase (36) or decrease heart rate by consuming 5 mg/kg caffeine (37).Beetroot-juice as a source of nitrate plays anti-inflammatory, antioxidant and anti-hypertensive effects due to its bioactive component (29). Beetroot-juice consumption can increase nitric oxide bioavailability due to inorganic nitrate and reduce arterial stiffness and improve endothelial (30-32). Although it is shown many beneficial effects of Beetroot-juice supplementation on endurance and cardiorespiratory parameters, the combination of Beetroot-juice supplement with other supplements including caffeine did not show any positive or negative effect on cardiorespiratory parameters, which suggests interaction between Beetroot-juice supplement and caffeine effect (33). Studies on acute and chronic supplementation with Beetroot-juice did not show beneficial effects of Beetroot-juice on performance in runners, moreover, supplementation time prior to physical activity is another effective factor and it is suggested that supplementation 90-120 min before activity will not provide sufficient time in order to reach nitrate peak level in blood (34-36).
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.
Type of Study: Research | Subject: Exercise Physiology

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