Effects of dietary supplements on athletic performance in elite soccer players: a systematic review

Figures & data

Figure 1. PRISMA Flow Diagram.

Table 1. Summary of the included studies.

Author	Population (age, sex, and level)	Region	Study design	Supplementation protocol (substance or nutrient, dose, and duration	Exercise test and outcomes measured	Synthesis of main findings	Overall bias
Caffeine
Astorino et al. (2012)	15 females, collegiate players (NAIA soccer team) (19.5 ± 1.1 years)	U.S.A.	Randomised, blind, placebo-controlled, crossover	Red Bull® (80 mg caffeine, 1.3 mg/kg +1 g taurine +27 g carbohydrates; 255 mL) vs Canada Dry® Ginger ale (190 mL) mixed with one package of lemon-flavored Crystal Light, 1 h before exercise	Agility t-test (mean sprint time, sec)	Red Bull® did not alter repeated sprint performance.	Some concerns
Bassini et al. (2013)	19 professional males, major soccer league team affiliated with the Brazilian Soccer Confederation (26.0 ± 1.6 years)	Brazil	Randomized, double-blind, placebo-controlled	Caffeine (5 mg/kg) vs lactose (1 g), 1 h before exercise	Yo-Yo IR2 (velocity, km/h; distance, m)	Caffeine supplementation did not affect the Yo-Yo IR2 performance.	Some concerns
Del Coso et al. (2012)	19 semiprofessional males, soccer team (21 ± 2 years)	Spain	Randomised, double-blind, placebo-controlled, crossover	Caffeine-containing energy drink (630 ± 52 mL; volume individually set to 3 mg caffeine/100 mL) – sugar-free Red Bull® vs sugar-free decaffeinated Pepsi® (same volume), ingested 1 h before exercise	CMJ (height, cm; power output, kW), RSA (7 × 30 m) (average peak speed and maximal speed, km/h), simulated soccer game (2 × 40 min) (total distance covered, m; distance covered at different speeds, m; number of sprint bouts)	The caffeine-containing energy drink enhanced jump height, increased the ability to repeatedly sprint and the distance covered at high intensity during a simulated soccer game.	Some concerns
Guerra Jr et al. (2018)	12 professional males, soccer team (23.83 ± 5.06 years)	Brazil	Randomised, double-blind, placebo-controlled, crossover	Caffeine (5 mg/kg) diluted in 250 mL of artificially sweetened water vs 250 mL of artificially sweetened water, 1 h before exercise	CMJ (height, cm)	Acute plyometric and sled towing stimuli enhances jump performance, and this is augmented by caffeine ingestion.	Some concerns
Lara et al. (2014)	18 females, soccer team (21 ± 2 years)	Spain	Randomized, double-blind, placebo-controlled, crossover	Energy drink [caffeine (3 mg/kg), taurine (18.7 mg/kg), sodium bicarbonate (4.7 mg/kg), and L-carnitine (1.9 mg/kg)] vs identical drink with no caffeine, ingested 1 h before exercise	CMJ (height, cm; peak power, W/kg), RSA (7 × 30 m) (average peak speed and maximal speed, km/h), and simulated soccer game (2 × 40 min) (total distance covered, m; distance covered at different speeds, m; number of sprint bouts; maximal speed, km/h)	Ingesting caffeine in the form of an energy drink enhanced jump height, the ability to perform repeated sprints, the total distance covered, and the distance covered at high intensity and sprint velocity during a simulated game.	Some concerns
Ranchordas et al. (2018)	10 university-standard males (19 ± 1 years)	U.K.	Randomised, double-blind, placebo-controlled, crossover	Two pieces of gum containing caffeine (100 mg/piece; 2.7 ± 0.2 mg/kg with two pieces) and carbohydrates (2 g/piece) vs gum void of caffeine, chew for 5 min immediately after the warm-up	CMJ (height, cm), 20 m sprint (time, sec), and Yo-Yo IR1 (distance covered, m)	Chewing the caffeinated gums increased jump height by 2.2% and enhanced performance on the Yo-Yo IR1 by 2%, but the effects were small. No effects on 20 m sprint performance.	Some concerns
Creatine
Kim et al. (2021)	20 well-trained elite males, soccer team (20.70 ± 1.08 years)	Korea	Randomised, placebo-controlled	Creatine monohydrate (5 g, 4×/d) and sodium bicarbonate (0.075 g/kg, 4×/d) vs maltodextrin (same dosage), 7 days	10 m sprint (time, sec), 30 m sprint (time, sec), coordination test (time, sec), arrowhead agility test (time, sec), Yo-Yo IR1 (distance covered, m)	Creatine monohydrate and sodium bicarbonate supplementation improved 30 m sprint performance and agility.	Some concerns
Mujika et al. (2000)	17 highly trained males; soccer team competing at a national level (20.3 ± 1.4 years)	Spain	Randomised, double-blind, placebo-controlled	Creatine monohydrate (5 g, 4×/d) vs maltodextrin (same dosage), 6 days	CMJ (height, cm), RST [6 × 5 m and 6 × 15 m sprint test (time, sec)], IET (distance covered, m), Recovery CMJ (% of the performance attained in the resting CMJ)	Acute creatine supplementation favorably affected RST performance and a limited the decay in jumping ability after the IET.	Some concerns
Ramírez-Campillo et al. (2016)	30 females (22.9 ± 2.5 years)	Chile	Randomised, three-trial, double-blind, placebo-controlled	Phase 1: Creatine monohydrate (5 g, 4×/d) vs glucose (same dosage), 1 week Phase 2: Creatine monohydrate (5 g/d) vs glucose (same dosage), 5 weeks	Day 1: SJ (height, cm), CMJ (height, cm), 20 m sprint (time, sec), RAST [6 × 35 m maximal sprints (time, sec)]; Day 2: 20 cm and 40 cm drop jump reactive strength index (speed, mm/ms), peak jump power (W), peak jump power load (W); Day 3: unilateral 20 cm drop jump reactive strength index (right and left leg) (speed, mm/ms), change-of-direction speed test (i.e. Illinois test) (time, s), 20 m multistage shuttle run test (time, min)	Creatine supplementation enhanced jump performance variables and RAST results.	Some concerns
Zajac et al. (2020)	16 well-trained elite males (25.6 ± 3.7 years)	Poland	Randomised, placebo-controlled	Magnesium creatine chelate (1375 mg, 4×/d; 0.07 g/kg/d) vs corn starch, 16 weeks	RAST [TT (s), First 35-m sprint (time, s), Sixth 35-m sprint (time, s), MP (W), AP (W)]	The long-term low dose of magnesium creatine chelate supplementation improved RAST performance.	Some concerns
Protein
Kritikos et al. (2021)	10 well-trained males (21 ± 1.5 years)	Greece	Randomised, three-trial, double-blind, placebo-controlled, crossover	Whey protein isolate or soy protein isolate drink (the protein content in each drink was individually adjusted to account for a total intake of 1.5 g/kg/d) vs energy-matched drink (maltodextrin; total protein intake of 0.8–1.0 g/kg/d), 10 days	MVIC (Nm), concentric and eccentric isokinetic peak torque of the KE and KF of the dominant and non-dominant limb (Nm), CMJ (height, cm), 10 m sprint (time, sec), 30 m sprint (time, sec), RSA fatigue index (%)	Increasing daily protein intake to 1.5 g/kg through ingestion of either whey or soy protein supplements mitigates field performance deterioration during successive speed-endurance training sessions.	Low
Poulios et al. (2018)	20 competitive males (20.6 ± 1.1 years)	Greece	Randomised, double-blind, placebo-controlled, crossover	Match days: milk protein concentrate drink [1.15 g/kg/d (80% casein and 20% whey)] vs energy-matched drink (1.37 g/kg/d of maltodextrin), consumed as doses (immediately after the game, 3 h after, and 6 h after) Training days: milk protein concentrate drink [0.26 g/kg/d of protein (80% casein and 20% whey)] vs energy-matched drink (0.31 g/kg/d of maltodextrin)	10 m sprint (time, sec), 30 m sprint (time, sec), CMJ (height, cm), concentric strength of the KE of the dominant and non-dominant limb (Nm/kg), eccentric strength of the KF of the dominant and non-dominant limb (Nm/kg)	Protein supplementation may improve football locomotor activity during game 2 and seems to prevent a decline of KE and KF peak torque during recovery.	Low
Carbohydrate and Electrolyte drinks
Abbey et al. (2009)	10 highly trained competitive males (22.5 ± 3.3 years)	U.S.A.	Randomised, blind, three-trial, placebo-controlled, crossover	Clover honey mixed with lemonade-flavored drink sweetened with NutraSweet +110 mg sodium/240 mL fluid [6% carbohydrates, 0.5 g/kg; 8.8 mL fluid/kg)] vs commercially available sports drink (Gatorade) (6% carbohydrates, 0.5 g/kg) vs lemonade-flavored drink sweetened with NutraSweet, taken 30 min before exercise and at the 10-min half-time	Soccer-simulation test [high-intensity run (5 sets), agility drill test (time, sec), ball-shooting drill test, and PSR test to exhaustion]	Acute ingestion of honey and a carbohydrate sports drink before and during the halftime of a soccer-simulation test did not improve performance.	Some concerns
Tart Cherry
Abbott et al. (2019)	10 professional males, reserve team of an English Premier League Club (19 ± 1 years)	U.K.	Randomised, double-blind, placebo-controlled, crossover	Tart cherry juice concentrate [22 g carbohydrates; 30 mL (equivalent to 100 sour cherries), 2×/d] mixed with water vs isocaloric cherry-flavored drink (22 g sucrose), before and after a 90-min match, and 12 h and 36 h after the match	CMJ (height, cm) and RSI [jump height (cm)/contact time (sec)]	Tart cherry juice did not hasten recovery after a soccer match.	Some concerns
Beetroot Juice
Daab et al. (2021)	13 males, semiprofessional Tunisian senior squad (22.12 ± 0.56 years)	Tunisia	Randomised, double-blind, placebo-controlled, crossover	Nitrate-rich beetroot juice (150 mL, 2×/d; 500 mg nitrates/d), 7 days	LIST [SJ (height, cm), CMJ (height, cm), MVC of knee extension (N), 20 m sprint (time, sec)]	Chronic beetroot juice supplementation may maintain better performance during the recovery period.	Some concerns
Sodium Bicarbonate (combined with other minerals)
Chycki et al. (2018)	26 well-trained males, elite Polish league	Poland	Randomised, placebo-controlled	Sodium bicarbonate (3000 mg), potassium bicarbonate (3000 mg), calcium phosphate (600 mg) + calcium citrate (400 mg), potassium citrate (1000 mg), magnesium citrate (1000 mg), 2×/d vs corn starch; 9 days	RAST [6 × 30 m running test (time, sec)]	Chronic supplementation with sodium and potassium bicarbonate fortified with calcium phosphate, calcium citrate, potassium citrate, and magnesium citrate increased RAST performance.	Some concerns
Yohimbine
Ostojic (2006)	20 top-level males, First Professional League of Serbia & Montenegro (EXP: 24.3 ± 3.2 years; CON: 23.8 ± 2.9 years)	Servia	Randomised, double-blind, placebo-controlled	Yohimbine (10 mg, 2×/d) vs cellulose, 21 days	Bench press test (repetitions, n), leg press test (repetitions, n), vertical jump test (height, cm), dribble test (time, sec), sprint-power test (time, sec), endurance shuttle-run test (time, sec)	Yohimbine supplementation did not produced marked changes in general or sport-specific exercise performance indicators.	Some concerns
Resurgex Plus®
Arent et al. (2010)	22 fit males, Division I college soccer team (EXP: 19.5 ± 0.4 years; CON: 19.4 ± 0.4 years)	U.S.A.	Randomised, blind, placebo-controlled	Resurgex Plus® [(75 mg CoQ10, 500 U SOD/Gliadin, 1750 mg ornithine ketoglutarate, 300 mg L-Carnitine, 100 mg nucleotides, 750 mg d-ribose, 500 mg L-glutamine, 100 mg beta-glucans, 12.5 mg fruit polyphenols, and 1750 mg BCAA), 2×/d] vs isocaloric equivalent without Resurgex Plus®; 20 days	Graded maximal treadmill test to exhaustion [VLT (km/h), TTE (min)]	Preseason training resulted in significant improvements in VLT, and TTE. Supplementing with Resurgex Plus® may enhance some of these effects; however, none reached statistical significance.	Some concerns

Data are presented as mean ± SD or mean ± SEM. AP: Average Power; BCAA: Branched Chain Amino Acids; CMJ: Countermovement Jump; CON: Control Group; EXP: Experimental Group; IET: Intermittent Endurance Test; KE: Knee Extensors; KF: Knee Flexors; LIST: Loughborough Intermittent Shuttle Test; MP: Max Power; MVC: Maximal Voluntary Contraction; MVIC: Maximal Voluntary Isometric Contraction; PSR: Progressive Shuttle-Run; RAST: Running-based Anaerobic Sprint Test; RSI: Reactive Strength Index; RST: Repeated Sprint Test; SJ: Squat Jump; TT: Total Time; TTE: Time to Exhaustion; VLT: Velocity at Lactate Threshold; VO2max: Maximal Oxygen Consumption; Yo-Yo IR1: Yo-Yo Intermittent Recovery Level 1; Yo-Yo IR2: Yo-Yo Intermittent Recovery Level 2.

Figure 2. Risk of Bias Tool V.2. (a) Risk of bias per domain across studies with a parallel design; (b) Risk of bias per domain across studies with a crossover design.