Beta-alanine
Evidence: moderate
Strong evidence, but for a window (~1-4 minute efforts) that barely overlaps distance running. Relevant at most to the track mile and the final kick.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Beta-alanine has strong evidence, classed Group A, but for a window that barely overlaps distance running. It raises muscle carnosine, an intracellular buffer against the acidosis of hard efforts (Trexler et al. 2015). The dose is 3.2 to 6.4 g per day split through the day, loaded over at least four weeks; the main side-effect is harmless skin tingling, reduced by splitting doses.
The benefit concentrates in maximal efforts of about one to four minutes, around 2.85% overall, and is significant between 60 and 240 seconds but not below 60 (Hobson et al. 2012). For running that points to the 800 m to about 3000 m range and to final-kick scenarios, with little to offer the half-marathon or marathon. The effect is also somewhat stronger for exercise capacity than for race-day performance, so even within its window it is a modest aid. For most distance runners it is the wrong tool; for a track miler it is a reasonable one, and it pairs mechanistically with sodium bicarbonate, which buffers outside the cell.
How to take it
It is a loading supplement, not a pre-race one
Beta-alanine works by saturating muscle carnosine over time, so it is taken daily for at least four weeks, not before a session. The dose is 3.2 to 6.4 g/day split into several smaller doses through the day; splitting it, or using a sustained-release form, reduces the harmless skin-tingling (paraesthesia) that larger single doses cause. Once muscle carnosine is raised it washes out slowly, so the effect persists for weeks after stopping. Taking it on race morning does nothing.
Why it barely matters for distance running
The buffering carnosine provides only helps when intramuscular acidosis is the limiter, which is the case in maximal efforts of roughly one to four minutes, not in the predominantly aerobic efforts of 5 km and beyond. The honest reading for a distance runner: relevant only if you race the 800 m to about 1500 m, or want a sharper finishing kick, and not worth taking for anything longer. Where it is used, it pairs mechanistically with sodium bicarbonate, which buffers in the blood outside the muscle while carnosine buffers inside it, and the two are sometimes combined for middle-distance track racing with some evidence of an additive effect.