International society of sports nutrition position stand: Beta-Alanine

Carnosine (β-Alanyl-L-histidine) is a naturally occurring dipeptide with numerous potential physiological functions and is formed by combining its constituent amino acids, L-histidine and beta-alanine, with the assistance of the enzyme carnosine synthetase. Carnosine is predominantly stored within skeletal muscle, and can vary widely between species [16]. Carnosinase, the enzyme that catalyzes the breakdown of carnosine, is present in serum and various tissues in humans, but is absent in skeletal muscle [25] and many animals. It is important to note that carnosinase is not present in most non-primate mammals [26], which must be considered when evaluating carnosine supplementation and data obtained from animal models. Therefore, oral carnosine supplementation is an inefficient method of augmenting muscle carnosine levels in humans, as ingested carnosine is ultimately metabolized before reaching skeletal muscle [27].

Carnosine’s role as an intracellular proton buffer was first identified by Severin et al. in 1953 [28], who demonstrated that the absence of carnosine resulted in more rapid fatigue and acidosis. By virtue of a pKa of 6.83 and high concentrations in muscle [29], carnosine has been shown to be more effective at sequestering protons than either bicarbonate (pKa 6.3) or inorganic phosphate (pKa 7.2), the other two major physio-chemical buffers, over the physiological pH range. With respect to carnosine’s structure, nitrogen atoms on the imidazole ring can readily accept a proton at physiological pH, and therefore it has been suggested that carnosine buffering precedes involvement of the bicarbonate buffering system during exercise [30]. Preliminary estimates of what contribution carnosine may play in buffering suggested as much as 40 % of the buffering capacity of muscle [31] when evaluated in animals; more recent research in humans has indicated the contribution may be as low as 7 % [15]. More evidence documenting the contribution of carnosine in muscle buffering is needed to further identify its role in exercise performance. Nonetheless, beta-alanine supplementation has been shown to increase muscle carnosine concentrations [1, 3] and attenuate exercise-induced reductions in pH [32], supporting the concept that carnosine plays a significant role in buffering exercise-induced acidosis.

The potential physiological roles of carnosine extend beyond its function as a proton buffer. Previous research has suggested that reactive oxygen species (ROS), which are produced at an elevated rate during exercise [33], may contribute to muscle fatigue and exercise-induced muscle damage under certain circumstances [34, 35]. Carnosine has been shown to act as an antioxidant by scavenging free radicals and singlet oxygen [36, 37], thereby reducing oxidative stress. Carnosine can further reduce oxidative stress by chelating transition metals, such as copper and iron [37]. In doing so, these transition metals are prevented from reacting with peroxides in the Fenton reaction, which results in the production of free radicals. Carnosine is abundant in human skeletal muscle, and may influence these contributors to fatigue and oxidative stress by buffering excess protons [28], scavenging free radicals [36, 37], and chelating transition metals [37]. As the rate-limiting precursor to carnosine synthesis, beta-alanine supplementation has been shown to consistently elevate carnosine in a variety of populations, and may therefore improve performance during high-intensity exercise and/or enhance the quality of training in athletes participating in strength and power sports [38].

The supplementation strategy for beta-alanine is important to maximize its effects. To date, research suggests that beta-alanine requires a chronic loading dose of 4 to 6 g daily in divided doses of 2 g or less, for a minimum of two weeks (which results in a 20-30 % increase in muscle carnosine concentrations) [4], with greater benefits seen after 4 weeks (40-60 % increase) [19, 39]. To increase muscle carnosine, a larger dose of 6 g, divided into 4 equal doses would be more advantageous. Additionally, if supplementing with a non-time release version, consuming a total daily dose of 6 g would be important for augmenting muscle carnosine [40]. Single large boluses of beta-alanine have been shown to induce paraesthesia (i.e. tingling), and have not been effective for performance outcomes likely due to strong paraesthesia, rapid changes in pH, higher excretion rates, and inability to effectively load the muscle contents. Combining beta-alanine consumption with a meal during beta-alanine loading has also been shown to be effective for further augmenting muscle carnosine levels [41]. In addition, a recent meta-analysis [42] suggested that supplementation with a total ingestion of 179 g of beta-alanine (the average dose across all studies) resulted in a median performance improvement of 2.85 % compared with a placebo. Washout time, or time required for values to return to baseline, may vary between non-responders and responders, requiring 6 to 15 weeks to return to normal [4]. Despite these findings, the maximal concentration or retention of carnosine in human muscle is not well known; thus, we cannot yet provide information on the optimal loading or maintenance doses.

Paraesthesia (i.e., tingling) is the most widely known side effect of beta-alanine and is commonly experienced in individuals consuming more than 800 mg of beta-alanine in a non-sustained release form [1]. It appears that the symptoms of paraesthesia are substantially reduced with the use of sustained-release formulations. In studies using the non-sustained release supplement, paraesthesia has generally been reported to disappear within 60 to 90 min following supplementation [40]. It is hypothesized that beta-alanine activates Mas-related genes (Mrg) [43], or sensory neuron specific G-protein coupled receptors. Specifically, MrgD, which is expressed in the dorsal root ganglion, terminates in the skin [44]. It is likely that activation of MrgD from beta-alanine results in paraesthesia on the skin. To date, there is no evidence to support that this tingling is harmful in any way. The paraesthesia side effect is typically experienced in the face, neck, and back of hands. Although not all individuals will experience paraesthesia, it is typically dose-dependent, with higher doses resulting in greater side effects. Recent data also suggests that males of Asian descent may experience a reduced effect, with Asian females experiencing greater paraesthesia [45]. Moreover, there is no known mechanism to explain why certain individuals may be predisposed to experiencing paraesthesia. Currently, there is no safety data on the long-term use of beta-alanine (i.e., > 1 year). However, due to the non-essential nature of this constituent (i.e., beta-alanine is produced endogenously), the likelihood of safety concerns are low.

A secondary effect of beta-alanine supplementation is a potential decrease in taurine concentrations. Beta-alanine and taurine share the same transporter (Tau-T) into skeletal muscle, with beta-alanine thereby inhibiting taurine uptake within the muscle [46]. In animal models, beta-alanine has been shown to decrease circulating taurine levels by about 50 % [47]. Interestingly, Harris et al. [1] reported that 4 weeks of beta-alanine supplementation (10–40 mg∙kg⁻¹bw) resulted in an increase in plasma taurine concentration; however, there was no significant decrease in muscle taurine content. While taurine has a number of essential physiological functions, to date there is no human data to support decreases with beta-alanine supplementation. Additionally, when extrapolated to humans, the decrease in taurine would not be of physiological significance.

To gain a better consensus of published findings, this review includes an analysis of the relative effects (RE) of literature obtained from PubMed and Google Scholar databases. The primary search terms included beta-alanine AND supplementation AND carnosine AND exercise. The search was limited to articles published as of March 2015 and written in English. To construct figures, literature with similar outcome variables was reviewed to identify studies evaluating the effects of beta-alanine supplementation for (a) open-ended exercise tasks, such as time to exhaustion (TTE), (b) fixed end-point exercise such as time trials, or (c) indices of neuromuscular fatigue.

To graphically depict the RE of beta-alanine in in comparison to placebo, RE was calculated using the following equation [48, 49]:

Where Pre_PLis the pre-test value in the placebo group, Post_PL is the post-test value in the placebo group, Pre_BA is the pre-test value in the beta-alanine group, and Post_BA is the post-test value in the beta-alanine group.

For Figures 1 and 3, an RE greater than 100 represents an increase or improvement in performance versus a placebo group. In Fig. 2, an RE less than 100 represents an improvement for fixed end-point tests, such as cycling time trials, where participants completed their work tasks faster.

It has been suggested that chronic beta-alanine supplementation improves high-intensity exercise performance by increasing muscle carnosine content, thereby enhancing intracellular proton buffering [50, 51]. Excess protons are also buffered independently of carnosine by a number of physicochemical buffering constituents; extracellular bicarbonate is the most relevant for increasing muscle buffering capacity [52], thereby acting to maintain intramuscular pH. As a result of augmented muscle buffering and mitigating H⁺ accumulation, beta-alanine has been suggested to be most beneficial in activities limited by acidosis, generally ranging from 2 to 4 min [25]. A collective view of the literature on anaerobic (0–4 min) and aerobic performance, neuromuscular fatigue, strength, and tactical challenges has been included.

The combined effects of beta-alanine with other ergogenic aids, such as sodium bicarbonate, creatine, and multi-ingredient pre-workout formulas, have gained popularity. Due to the potential positive effects of beta-alanine during high-intensity exercise, it has been hypothesized that combining it with other ergogenic aids may further augment performance and proton buffering.

Sodium bicarbonate (SB) supplementation has been shown to acutely increase bicarbonate levels, blood pH, and high-intensity exercise performance [81], prompting interest in combined supplementation with beta-alanine. Sale et al. [68] first examined the effects of this combination on exercise performance and showed that beta-alanine supplementation alone improved performance on a cycling test at 110 % of maximal power output, and that there was a 70 % probability of an additive effect of beta-alanine + SB compared to beta-alanine alone. Tobias et al. [82] investigated the effects of beta-alanine, SB, or the combination on repeated upper-body Wingate performance, separated by 3 min of rest. Both beta-alanine and SB improved mean power output, but the results for the beta-alanine + SB group were superior, but not significant, compared to either supplement alone. Despite non-significant differences between groups, authors of other studies have calculated the probability of an additive effect with combined beta-alanine and SB supplementation. In a 2,000-m rowing time trial, Hobson et al. [65] used magnitude-based inferences to determine that beta-alanine was very likely to improve time trial performance (96 % chance of positive effect), SB was likely to improve performance (87 % chance), and that adding acute SB supplementation to chronic beta-alanine consumption had a small, possibly beneficial affect compared to beta-alanine alone (64 % probability). In swimmers, de Salles Painelli et al. [62] showed a 71.8 % and 78.5 % probability of an additive effect on 100-m and 200-m sprints, when adding SB to beta-alanine supplementation. In contrast to these studies, other findings do not suggest a synergistic effect between beta-alanine and SB.

In a series of two repeated 100-m sprints in swimmers, Mero et al. [83] showed that SB supplementation alone attenuated increases in sprint time for the second sprint, but neither beta-alanine nor beta-alanine + SB resulted in significant improvements compared to placebo. Ducker et al. [84] investigated the efficacy of beta-alanine and SB in the context of a repeated sprint test consisting of three sets of 6 (18 total), 20-m sprints. Results demonstrated that SB supplementation improved performance more than placebo, beta-alanine, or a combination of beta-alanine and SB. Saunders et al. [85] had participants complete a repeated sprint protocol (five bouts of 6-s sprints) before, in the middle, and after a simulated football game in hypoxic conditions. Results indicated that neither beta-alanine, SB, nor beta-alanine plus SB improved performance on the sprint test. Bellinger et al. [86] showed that SB improved mean power output on a 4-min cycling test, but beta-alanine did not. While not statistically significant, subjects consuming beta-alanine + SB did improve power slightly more than those consuming SB alone, and 6 of 7 participants consuming beta-alanine saw an increase in average power output after additional supplementation with SB. It is also important to note that the protocols employed by Ducker et al. [84] and Saunders et al. [85] consisted of very short bouts (<7 s), in which proton buffering would not be the primary factor limiting performance.

Collectively, the body of literature suggests a modest additive effect when adding SB to beta-alanine supplementation in exercise bouts in which metabolic acidosis may be performance-limiting. While this additive benefit is not typically revealed with traditional statistical analyses, studies using magnitude-based inferences have suggested that a modest additive effect is likely to exist [62, 65, 68]. The studies reviewed have used supplement dosages ranging from 4.8-6.8 g/kg/day of beta-alanine for at least 28 days, and 0.3-0.5 g/kg of SB taken acutely. However, the only study to indicate a statistically significant synergistic effect of beta-alanine and SB [82] employed a unique dosing protocol for SB, providing daily doses of 0.5 g/kg/day for seven days, whereas other studies typically provide a dose of 0.3 g/kg acutely in the hours preceding the exercise bout. Individual responses to SB supplementation may vary, likely due to side effects including headache and gastrointestinal discomfort [68, 85, 87]. In terms of practical application, those wishing to combine beta-alanine and SB supplementation must carefully evaluate the dosage and timing with which SB is consumed and weigh the modest additive benefit against the risk of potentially ergolytic side effects.

Given the proton-buffering capacity of muscle carnosine [51], beta-alanine is most commonly purported to improve performance in exercise of high enough intensity to induce intramuscular acidosis. Creatine supplementation has been consistently shown to improve high-intensity exercise performance, primarily by increasing phosphorylcreatine and adenosine triphosphate (ATP) availability [88]. The first study investigating co-ingestion of these ingredients was reported in a published abstract by Harris et al. [89], finding that power output in a 4-min cycling test was improved more by creatine + beta-alanine than creatine alone. Similarly, Hoffman et al. [76] showed greater improvements in lean mass, fat mass, and strength in creatine + beta-alanine compared to creatine alone. Notably, these studies did not include a treatment arm ingesting beta-alanine alone. Zoeller et al. [58] investigated the effects of beta-alanine and creatine on performance on a graded, maximal exercise test on a cycle ergometer. No significant group effects were shown (creatine, beta-alanine, creatine + beta-alanine, or PL), but authors noted that the creatine + beta-alanine did have significant within-group improvements for 5 of the 8 outcomes measured, compared to only one in the beta-alanine group and two in the creatine group. Stout et al. [71] showed that beta-alanine and creatine + beta-alanine improved PWC_FT compared to creatine and PLA. There was no evidence of a synergistic effect on this outcome, as CRE + beta-alanine was not significantly different than beta-alanine alone. Kresta et al. [90] investigated both aerobic and anaerobic exercise outcomes. The creatine group trended toward an increase in VO₂max, while the beta-alanine group trended toward an improvement in rate of fatigue on a series of two Wingate tests. However, no significant effects on performance were noted for any treatment arm, and results did not suggest a synergistic effect between creatine and beta-alanine.

Two studies have shown additive ergogenic effects when beta-alanine is combined with creatine supplementation [76, 89], but did not include a treatment group ingesting beta-alanine only. Other studies including a beta-alanine treatment arm have not demonstrated a synergistic effect between beta-alanine and creatine [71, 90]. Despite promising findings from initial studies [76, 89], more research is needed to evaluate potential synergy between creatine and beta-alanine supplementation. Based on the ergogenic mechanisms of each ingredient, performance improvements are more likely to occur in high-intensity bouts of exercise, and studies investigating exercise bouts over 15 min in duration have not shown beta-alanine + creatine to be significantly more effective than placebo [58, 90].

Multi-ingredient pre- and post-workout supplements have become increasingly popular, with formulations that include a number of purportedly ergogenic ingredients including creatine, caffeine, branched-chain amino acids, whey protein, nitric oxide precursors, and other isolated amino acids [91‐98]. Such supplements are typically consumed once per day prior to training, with beta-alanine doses generally ranging from 2 to 4 g single boluses. When ingested acutely before exercise, previous studies have shown these multi-ingredient supplements to improve muscular endurance [92, 98], running time to exhaustion [91], and power output [98]. Some studies have documented improvements in subjective feelings of energy and focus [91, 92], while Gonzalez et al. [98] did not. When taken chronically for a period of 4 to 8 weeks, multi-ingredient pre-workout supplements have been shown to increase measures of strength [93, 94, 97], power output [96], and lean mass [93‐95]. In contrast, Outlaw et al. [99] found no significant benefit for body composition, strength, or power output with ingestion of a multi-ingredient supplement versus placebo. While the supplement group tended to improve leg press strength to a greater degree than the placebo group, this difference was not statistically significant (p = 0.08). These discrepant findings may be attributed to the short duration of supplementation (8 days), or the substantial improvements in lean mass, strength, and peak power output displayed by the placebo group.

Overall, the body of literature suggests that acute and chronic ingestion of multi-ingredient pre-workout supplements can contribute to improvements in performance and body composition. It is difficult to attribute these ergogenic effects directly to beta-alanine, as multi-ingredient supplements include a wide range of ergogenic ingredients that may improve performance independently (e.g., caffeine, creatine, etc.). It typically takes a number of weeks (at least 2 weeks) for beta-alanine supplementation to yield meaningful increases in muscle carnosine content [3, 19]. As such, it is unlikely that beta-alanine is the primary ingredient improving performance outcomes in studies utilizing acute, one-time supplementation. In studies extending over 4 to 8 weeks, the likelihood of beta-alanine contributing to improvements in performance and indirect effects on body composition is greater. While it is difficult to determine the relative contributions of individual ingredients, research has demonstrated that multi-ingredient pre-workout supplements containing 2 to 4 g of beta-alanine are safe and efficacious when taken acutely, or chronically for up to 8 weeks.

Decades of literature support a potential for carnosine to influence some mechanisms related to health including antioxidant properties, anti-aging, immune enhancing, and neurotransmitter actions. However, the majority of these health benefits have been explored in vitro and in animal models. Carnosine is widely considered an important anti-glycating agent that serves to prevent reactions that threaten to impact the structure and function of proteins in the body. Advanced glycation end products are associated with the aging process and diabetic complications, but carnosine is thought to reduce the formation of these end products [100, 101]. Previous research has also indicated that carnosine acts as a “sacrificial peptide,” reacting with carbonyl groups of aldehydes, ketones, and proteins to prevent damage to proteins [102, 103].

Carnosine is also known to be an antioxidant that is capable of preventing the accumulation of oxidized products derived from lipid components of biological membranes [104, 105]. The antioxidant mechanism of carnosine has been postulated to be due to metal chelation or free radical scavenging [106]. The combination of histidine-containing compounds, such as carnosine, at near physiological concentrations, have resulted in synergistic antioxidant activity [37]. Minimal data in humans exists regarding the potential antioxidant effect of increasing muscle carnosine vis-a-vis beta-alanine. Initial research suggests that beta-alanine may effectively reduce lipid peroxidation and mitigate accumulation of free radicals when combined with aerobic exercise in men and women [107, 108]. Future research evaluating potential anti-aging effects and the impact of potential antioxidant properties in humans would be important to explore, especially due to the positive effects beta-alanine has shown in older populations [24, 73]

It is widely accepted that as a result of increases in muscle carnosine concentration, the primary mechanism driving enhanced performance is the improvement in H⁺ buffering within skeletal muscle. Interestingly, humans also have carnosine within the brain, eye, and heart tissue [37, 109]. Therefore some initial data has explored the neuronal effects of carnosine [80, 110], as well as potential effects on cardiac tissue and heart rate [60]. Future research exploring the effects of beta-alanine to induce changes in carnosine concentrations in these tissues would be beneficial, as well as explorations of potential physiological effects in humans. An additional potential function of carnosine has been linked to improvements in calcium sensitivity in muscle fibers [111, 112]. As a result of improved calcium sensitivity, there may be a direct impact on muscular performance. This mechanism has not yet been fully explored in humans. One recent paper by Hannah et al. [113] suggests that an improvement in calcium kinetics is not the mechanism by which beta-alanine influences performance. Future studies should further explore this mechanism. Lastly, there is a need for long-term safety data on beta-alanine supplementation as well as more information on potential benefits in special populations such as elderly and tactical athletes.