Evidence explainerHMB (beta-hydroxy-beta-methylbutyrate)
HMB for Muscle After 50: Small Gains in Mass, Grip and Walking Speed Across 21 Trials
HMB disappoints in young lifters, but trials in older adults tell a more positive, if modest, story. Here is the size of the effect and what the studies used.
Key takeaways
- In a 2025 meta-analysis of 21 trials with 1,935 adults over 50, HMB increased appendicular muscle mass by 1.56 kg and lean mass by 0.28 kg [1].
- Handgrip strength rose by 0.54 kg, chair-stand time fell by 0.73 seconds and gait speed rose by 0.06 m/s [1].
- Subgroups taking 3 g/day for more than 12 weeks showed significant improvement [1].
- Calcium HMB at 3 g/day adds about 400 mg of calcium; the free acid form has none [2].
- A review of nine studies found 3 g/day well tolerated for 3 to 8 weeks, including in adults aged 62 to 81 [2].
The evidence, graded
Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.
- Grade BImprovedMuscle mass, strength and physical function in adults over 50HMB increased appendicular skeletal muscle mass (1.56 kg) and lean mass (0.28 kg), handgrip strength (0.54 kg), chair-stand time (-0.73 s) and gait speed (0.06 m/s).
- No effectNo effectFat-free mass and strength gains in young adults doing resistance trainingHMB produced a small gain in total body mass but no significant effect on fat-free mass, fat mass or one-rep-max strength.
What 21 trials found
A 2025 meta-analysis pooled 21 randomized trials in adults over 50 (n=1,935) [1]. HMB increased appendicular skeletal muscle mass by 1.56 kg and lean mass by 0.28 kg, handgrip strength by 0.54 kg and gait speed by 0.06 m/s, and cut chair-stand time by 0.73 seconds [1].
The effects are small, and the confidence intervals for muscle mass were wide [1]. Subgroups at 3 g/day and those lasting more than 12 weeks showed significant improvement [1]. We grade the evidence B.
Why the result differs from young lifters
In young adults doing resistance training, a 2020 meta-analysis found no significant effect of HMB on fat-free mass or strength [3]. ODS notes that experts hypothesize HMB helps muscle that is stressed or damaged [2]. Why results differ between young and older adults has not been established.
For how HMB compares with the most-studied muscle supplement, see HMB vs creatine.
How the studies used it
HMB studies used 1.5 to 6 g/day, most commonly 3 g, a dose that gave results equivalent to 6 g and better than 1.5 g [2]. The ISSN suggests 3 g/day split into three 1 g servings [2].
Calcium HMB is about 13% calcium by weight, so 3 g/day adds about 400 mg of calcium to the diet; people limiting calcium can use the calcium-free free acid form [2]. That matters for anyone also taking a calcium supplement; see calcium citrate or carbonate.
Safety
A review of safety data from nine studies found HMB well tolerated and safe at 3 g/day for 3 to 8 weeks in younger (18 to 47) and older (62 to 81) adults, with no adverse effects on blood chemistry or hematology [2]. There is no expert consensus on using HMB for several months or longer [2].
Protein and resistance training remain the foundation for muscle in later life; see how much protein builds muscle.
Quick answers
How much HMB do older adults take?
Most studies used 3 g/day, and the over-50 subgroups at 3 g/day showed significant improvement [2][1].
How long does HMB take to work?
In the 2025 meta-analysis, subgroups lasting more than 12 weeks showed significant improvement [1].
Does HMB work without exercise?
The abstract of the 2025 meta-analysis does not separate trials with and without exercise, so our sources cannot answer this [1].
Keep reading
Full monographs
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References
- [1]Effects of oral supplementation of β -hydroxy-β -methylbutyrate on muscle mass and strength in individuals over the age of 50: a meta-analysis. Front Nutr, 2025.
- [2]Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2024.
- [3]Supplementation with the Leucine Metabolite β-hydroxy-β-methylbutyrate (HMB) does not Improve Resistance Exercise-Induced Changes in Body Composition or Strength in Young Subjects: A Systematic Review and Meta-Analysis. Nutrients, 2020.