Benefits
Athletic performance — power and strength
A 2024 systematic review and meta-analysis (17 trials, 317 participants) found betaine (typically 2.5 g/day for at least 7 days) produced a significant but moderate improvement in maximal strength (standardized mean difference 0.47), driven mainly by lower-body strength, and a significant improvement in vertical jump. The same meta-analysis found no significant effect on upper-body strength, cycling sprint power, bench-press-throw power, or muscular endurance. The effect is real but selective, and it is smaller and less consistent than creatine's.
Body composition improvement
In a 6-week randomized trial of 23 strength-trained men, body fat percent, fat mass, and lean body mass improved significantly within the betaine (2.5 g/day) group but not the placebo group. The trial did not report a significant between-group difference in these body-composition measures, so the result should be read cautiously. A proposed mechanism is betaine's role as a methyl donor for creatine synthesis.
Homocysteine reduction (a cardiovascular risk marker)
Betaine is one of the most effective natural agents for reducing elevated homocysteine — a cardiovascular risk factor. As the methyl donor for homocysteine remethylation to methionine via BHMT (betaine-homocysteine methyltransferase), betaine addresses homocysteine through a B-vitamin-independent pathway. Homocysteine reductions of roughly 10 to 20 percent are achieved with 1.5 to 6 g/day. Lowering homocysteine is a change in a blood marker: no trial has shown that betaine reduces heart attacks, strokes, or other cardiovascular events.
Methylation support and fatty-liver evidence (mixed)
Betaine is a methyl donor used in phosphatidylcholine synthesis and SAMe regeneration in the liver. Human evidence in fatty liver disease is mixed: a 12-month randomized placebo-controlled trial of high-dose betaine (20 g/day) in 55 NASH patients did not improve steatosis, fibrosis, or the NAFLD activity score versus placebo. More recent pilot trials at lower doses (2 to 8 g/day) reported reductions in ALT and other blood markers of liver injury, but these were small, mostly within-group comparisons rather than placebo-controlled results. Benefit on hepatic fat is not established.
Mechanism of action
BHMT-mediated homocysteine remethylation
Betaine donates a methyl group to homocysteine via betaine-homocysteine methyltransferase (BHMT) in the liver and kidneys, converting potentially harmful homocysteine back to methionine. This B-vitamin-independent remethylation pathway complements the folate/B12-dependent methionine synthase route, providing a backup mechanism particularly important when folate or B12 are insufficient.
Cellular osmolyte protection
Betaine accumulates intracellularly as an organic osmolyte, protecting cells from hypertonic stress by balancing water activity without disrupting protein structure. In muscle cells under the osmotic stress of intense exercise, betaine maintains cellular hydration, protein stability, and enzyme activity — improving muscle performance during high-intensity training.
Creatine synthesis substrate provision
Betaine provides methyl groups for guanidinoacetate methylation — the final step in creatine biosynthesis. By increasing the efficiency of the body's endogenous creatine production, betaine amplifies the cellular creatine pool and enhances the phosphocreatine energy system in muscle, contributing to the ergogenic effects observed in strength and power athletes.
Clinical trials
Within-subject crossover study in 12 recreationally trained men examining 14 days of betaine supplementation (1.25 g twice daily, 2.5 g total) on strength and power outcomes including bench press throw power, isometric bench press force, vertical jump power, and isometric squat force. (Lee et al. 2010, J Int Soc Sports Nutr)
12 recreationally trained men (mean age 21). 14-day intervention, within-subject design.
Betaine increased bench throw power, isometric bench press force, vertical jump power, and isometric squat force vs pre-supplementation values. No improvement in jump squat power or rep counts. Effects more pronounced in upper-body movements. Note: this was a randomized, double-blind, placebo-controlled crossover, but the sample was small (n=12) and a later meta-analysis found betaine's strength benefit is mainly in lower-body movements.
Randomized, placebo-controlled trial in 23 resistance-trained men receiving betaine (2.5 g/day, n=11) or placebo (n=12) during a 6-week periodized training program. Outcomes: body composition (bench press work capacity, body fat %, lean body mass, fat mass), homocysteine thiolactone (HCTL), training volume. (Cholewa et al. 2013, J Int Soc Sports Nutr)
23 resistance-trained men. 6-week intervention.
Body composition (body fat percent, fat mass, lean body mass) and arm size improved significantly within the betaine group but not the placebo group, and bench press work capacity was greater in betaine at two of three microcycles. Vertical jump power showed only a trend (p=0.07). Betaine attenuated the rise in urinary homocysteine thiolactone. There were no significant between-group differences in maximal strength (1RM bench press or squat).