Calcium hydroxymethylbutyrate

non-nutrient/non-botanicalprohexadione-calcium

What is it

Calcium beta-hydroxy-beta-methylbutyrate (calcium HMB) is the calcium salt of HMB, a metabolite of the essential branched-chain amino acid leucine. It is used as a supplement for muscle preservation, particularly in older adults, athletes, and clinical conditions involving muscle loss.

How it works

HMB is produced naturally in the body from leucine, with approximately 5% of dietary leucine being converted to HMB. HMB has anti-catabolic effects, reducing muscle protein breakdown through inhibition of the ubiquitin-proteasome pathway and reducing markers of muscle damage. It also has modest anabolic effects, supporting protein synthesis via mTOR pathway activation. Research suggests HMB is particularly effective at preserving lean muscle mass during periods of catabolic stress, including bed rest, illness, aging-related sarcopenia, and intense exercise training. It may reduce post-exercise muscle damage and accelerate recovery. The effects are most pronounced in untrained individuals, older adults, and clinical populations with muscle wasting. The ergogenic effects of HMB in trained athletes are debated, with some studies showing benefit and others showing no effect. In clinical nutrition, HMB has been incorporated into specialized formulas for cancer cachexia, COPD, AIDS-related wasting, and recovery from major illness. The calcium component contributes to total calcium intake.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Muscle preservation in aging (sarcopenia)

Grade B

Good evidence

Multiple trials show HMB supplementation preserves lean muscle mass and function in older adults, particularly when combined with vitamin D and protein.

Muscle preservation during bed rest

Grade B

Good evidence

HMB reliably reduces muscle loss during periods of immobilization or bed rest in clinical and research settings.

Reduced exercise-induced muscle damage

Grade B

Good evidence

Multiple trials show HMB reduces markers of muscle damage (creatine kinase, lactate dehydrogenase) and may speed recovery from intense exercise, particularly in untrained individuals.

Athletic performance and strength gains

Grade C

Moderate evidence

Evidence is mixed. Effects are most consistent in untrained individuals starting resistance training; effects in well-trained athletes are smaller and less consistent.

Clinical muscle wasting (cachexia)

Grade C

Moderate evidence

HMB-containing nutritional formulas (often with arginine and glutamine) have shown benefits in cancer cachexia, COPD, and HIV-associated wasting.

3 commercial forms

Calcium HMB

Standard supplemental form; oral absorption is moderate.

The most widely available and studied form. Standard dose 3 grams per day.

Free acid HMB (HMB-FA)

Higher and faster plasma peak than calcium HMB; lower doses may suffice.

Liquid or gel form with improved pharmacokinetics. Used in some athletic and clinical applications.

HMB in specialized nutrition formulas

Often combined with arginine, glutamine, and other amino acids.

Used in clinical nutrition for cachexia, wound healing, and recovery from major illness.

Dosage

Standard dose is 3 grams per day, typically divided into three 1-gram doses with meals. This dose is supported by most clinical research. Free acid HMB requires lower doses (about 2-2.5 grams per day) due to better bioavailability. There is no established RDA.

When and how to take it

Take 1 gram of calcium HMB three times daily with meals for the standard 3-gram daily dose. Timing around exercise (one dose pre-workout, one post-workout, one with another meal) is sometimes recommended for athletes. Consistent daily use for 2-12 weeks is typically needed to evaluate effects on muscle preservation or recovery.

Food sources

Food	Amount	%DV
Grapefruit (1 medium)	approx 0.1 mg HMB (minor source)	—
Catfish (3 oz)	approx 0.5 mg HMB	—
Alfalfa	Naturally contains HMB	—
High-protein foods (via leucine conversion)	Endogenous HMB production from dietary leucine	—

Safety

Calcium HMB is generally well tolerated. Side effects are uncommon and include mild gastrointestinal symptoms. The calcium content adds to total daily calcium intake. No serious adverse effects have been reliably associated with typical doses in clinical trials lasting up to a year.

Who should be cautious

People with hypercalcemia or kidney disease should be cautious due to calcium content. People taking other calcium supplements should consider total intake. Pregnancy and breastfeeding safety is not well established at supplemental doses. People with phenylketonuria should be aware that HMB itself is generally safe but check specific products. People with severe liver disease should consult a clinician.

Interactions

Calcium HMB has limited known drug interactions. The calcium component may interact with medications affected by calcium, including tetracyclines, fluoroquinolones, bisphosphonates, and levothyroxine; separate by 2 hours. HMB itself has minimal documented drug interactions.

Frequently asked questions

What is HMB?⌄

HMB (beta-hydroxy beta-methylbutyrate) is a metabolite of the amino acid leucine. About 5% of dietary leucine is converted to HMB in the body. It has anti-catabolic and modest anabolic effects on muscle.

How much HMB should I take?⌄

Standard dose is 3 grams per day of calcium HMB, divided into three 1-gram doses with meals. Free acid HMB doses are slightly lower (2-2.5 grams).

Does HMB build muscle?⌄

HMB primarily preserves muscle (reduces breakdown) rather than dramatically building muscle. Effects on muscle gains are modest and most pronounced in untrained individuals or those starting resistance training.

Is HMB worth it for athletes?⌄

For well-trained athletes, the ergogenic effects are modest and inconsistent. For untrained individuals, older adults, and those recovering from injury or illness, HMB has more robust benefits.

Is HMB safe to take daily?⌄

Yes, clinical trials lasting up to a year have shown excellent safety with daily HMB supplementation at standard doses.

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.