What is the bioavailability of beta-Hydroxy beta-Methylbutyrate (HMB)?

Bioavailability of Beta-Hydroxy Beta-Methylbutyrate (HMB)

The calcium salt form of HMB (CaHMB) has approximately 49-54% greater bioavailability than the free acid form (FAHMB) in standard dosing ranges, with peak plasma levels occurring within 1-2 hours after ingestion. 1

Pharmacokinetics of HMB

Absorption and Peak Levels

• HMB plasma concentration peaks at different times depending on formulation and dosage:
  • For 1g HMB: Peaks at approximately 120 nmol/ml at 2 hours post-ingestion 2
  • For 3g HMB: Peaks at approximately 488 nmol/ml at 1 hour post-ingestion 2
  • When consumed with glucose (3g HMB + 75g glucose): Peaks at 352 nmol/ml at approximately 2 hours 2

Half-Life and Clearance

• Plasma half-life of HMB is approximately 2.5 hours 2
• Plasma HMB returns to baseline levels approximately 9 hours after ingestion 2
• The calcium salt form (CaHMB) has lower systemic clearance compared to the free acid form (FAHMB), contributing to its higher bioavailability 1

Metabolism and Excretion

• After oral administration, only 14-29% of ingested HMB is excreted in urine 2
• Approximately 70-85% of ingested HMB is retained in the body for further metabolism 2

Factors Affecting HMB Bioavailability

Form of HMB

• The calcium salt form (CaHMB) demonstrates significantly greater bioavailability than the free acid form (FAHMB):
  • 49% greater at low doses
  • 54% greater at medium doses
  • 27% greater at high doses 1
• After intravenous administration, the relative bioavailability of CaHMB is 80% greater than FAHMB 1

Co-ingestion with Other Nutrients

• Glucose co-ingestion affects HMB pharmacokinetics:
  • Delays time to peak plasma concentration (from 1 hour to nearly 2 hours)
  • Reduces peak plasma concentration (from 488 to 352 nmol/ml)
  • Slightly increases half-life (from 2.38 to 2.69 hours) 2
  • Reduces area under the curve during the first 3 hours 2

Clinical Implications

• The standard therapeutic dose of HMB is 3g/day, which is sufficient to maintain or improve muscle mass and function in both health and disease 3
• In patients with pressure ulcers, HMB can be added to oral/enteral feeds along with specific amino acids (arginine and glutamine) to accelerate healing 4
• The higher bioavailability of CaHMB may be clinically relevant when considering supplementation protocols 1

Potential Pitfalls and Considerations

• The bioavailability data comes primarily from animal studies, with the most comprehensive data from rat models 1
• Timing of administration may be important due to the relatively short half-life of HMB
• Co-ingestion with glucose alters the pharmacokinetic profile, which may be relevant for timing of supplementation relative to meals 2
• Compliance issues have been reported in clinical trials using HMB supplementation 5

HMB's relatively high retention rate in the body (70-85%) suggests efficient utilization of this leucine metabolite, which may contribute to its reported effects on protein metabolism and muscle preservation.