β-Alanine supplementation increased physical performance and improved executive function following endurance exercise in middle aged individuals

Aging is often associated with a reduction in one’s ability to exercise. A common causative factor is age-related deterioration, known as sarcopenia, and changes in viable skeletal muscle [1]. It has been previously shown that there is a direct relationship between sarcopenia onset and depleted systemic carnosine [25]. Carnosine is a dipeptide synthesized by carnosine synthetase in the presence of β-Alanine and L-Histidine [4, 610] predominantly found within skeletal muscle. It functions to improve myofiber contractility via enhancing sarcomere sensitivity to calcium, as well as to maintain pH homeostasis [4, 6, 8, 1015]. By acting as a pH buffer, carnosine allows for larger accumulation of lactate during exercise by delaying the associated acidification of systemic pH known to have negative effects on exercise performance and cognition [2, 6, 12]. As carnosine concentrations become depleted as a result of sarcopenia, its ability to buffer pH becomes limited manifesting a quicker onset of acidosis [2, 3].

Systemic carnosine levels have been successfully elevated by supplementing β-Alanine, a non-essential amino acid and rate limiting factor in carnosine synthesis [8, 16], at 3.2 g/day and 6.4 g/day [10, 17]. Additionally, β-Alanine induced increases in systemic carnosine are sustained over a range of 4 months following supplementation [14]. Studies have been investigated β-Alanine supplementation in young adults in an effort to increase exercise performance via multiple dosing strategies and exercise modalities. Hill et al. [12] showed that increasing the dose of β-Alanine from 4.0 g/day to 6.4 g/day over 4 weeks improves total work done by high intensity, college aged cyclists. Multiple other studies have also found similar results with varying dosage strategies. For example, Hoffman et al [9] found that 6.0 g of β-Alanine for 28 days improved tactical performance and jumping ability, but not serial subtraction test time in soldiers. 6.4 g/day was found to improve upper-body Wingate bouts [18].

The improvements in exercise capacity seen in young adults led to investigation involving β-Alanine supplementation in aging adults to combat symptoms of sarcopenia [2, 4]. Studies of aging populations have used a variety of dosage schemes such as 1.6 g/day, 2.4 g/day and 3.2 g/day for a range of 28 to 84 days [24]. Despite the positive results seen in younger populations, only del Favero et al. [2] has directly tested muscle carnosine or endurance cycling ability in aging subjects. They found an 85.4% increase in gastrocnemius carnosine levels as well as improved endurance exercise capacity following 12 weeks of 3.2 g/day of β-Alanine supplementation [2]. Different variations of dosages and length of supplementation within aging populations have, however, shown significant increases in cycling ability without directly measuring intramuscular carnosine levels [3, 4].

Furthermore, exercise has shown to affect executive functioning, such as decision making and short term memory [19]. Interestingly, researchers have shown that carnosine also accumulates in the central nervous system, specifically the cerebral cortex [13, 14]. In cerebral tissue, carnosine acts as an anti-oxidant with neuro-protective properties [7, 9, 13, 20]. Hoffman et al. [21] used rats to show that 30 day β-Alanine supplementation increases carnosine concentrations in the cerebral cortex, hippocampus, amygdala, hypothalamus and thalamus when exposed to stress. In humans, however, a 28 day β-Alanine supplementation showed improved physical fitness performance in military personnel, yet provided only minor improvements in decision making and reaction time [9]. Further, a recently published study was also unable to demonstrate improved executive function when testing at time points immediately prior to and following exercise [22].

The present study was undertaken to further investigate the effect of β-Alanine supplementation on exercise endurance and executive function in a middle aged human population. Our primary outcome was exercise performance measured as time-to-exhaustion (TTE). Our secondary outcome was Stroop Test derived indices of executive function. We hypothesize that β-Alanine supplementation would (a) improve exercise performance and (b) attenuate the decline in post exercise executive function.