The intervention effect of L-leucine on sarcopenia syndrome in the elderly

L-leucine exhibits significant efficacy in intervening in age-related sarcopenia in older adults. Through its core mechanisms of "activating muscle protein synthesis + inhibiting muscle protein breakdown + improving muscle function," it slows muscle mass loss, enhances muscle strength and mobility, serving as a safe and effective nutritional intervention.

I. Core Intervention Mechanisms

1. Activating Muscle Protein Synthesis Pathways

L-leucine acts as a "key switch" for muscle protein synthesis in older adults, efficiently activating the mTOR signaling pathway to promote ribosome assembly and synthesis of structural proteins such as actin and myosin. Due to age-related decline in mTOR pathway sensitivity, L-leucine supplementation specifically enhances pathway activity, increasing muscle protein synthesis rates by 25%–35% and counteracting age-associated reductions in synthetic efficiency.Additionally, it boosts branched-chain amino acid transaminase activity, providing sufficient raw materials for muscle synthesis and reducing age-related natural muscle loss (from 1%–2% annually in healthy older adults to 0.3%–0.5% with intervention).

2. Inhibiting Muscle Protein Breakdown

Older adults experience heightened muscle catabolism. L-leucine reduces muscle protein degradation by inhibiting the ubiquitin-proteasome system (the core pathway of muscle breakdown). It lowers the expression of muscle-specific ubiquitin ligases (e.g., MAFbx, MuRF1), decreasing muscle breakdown rates by 20%–25%. It also regulates insulin sensitivity, indirectly inhibiting muscle consumption via gluconeogenesis.

3. Improving Muscle Function and Mobility

L-leucine enhances muscle mitochondrial function, increasing ATP production in muscle fibers to improve endurance. It promotes proliferation and differentiation of muscle satellite cells (muscle repair stem cells), repairing damaged muscle fibers and enhancing muscle contractile strength. Furthermore, it alleviates the inflammatory microenvironment in aged muscles, reducing damage to muscle function from pro-inflammatory factors.

II. Specific Manifestations of Intervention Effects

1. Increased Muscle Mass and Strength

Muscle Mass: Daily supplementation of 12–20 g L-leucine for 12 weeks increases appendicular skeletal muscle mass in older adults by 1.5%–3.0% (measured by DEXA), with more significant improvements in lower limb muscles (quadriceps, gastrocnemius).

Muscle Strength: Grip strength increases by 8%–15%, and lower limb knee extension strength improves by 10%–20% (measured by dynamometry), effectively addressing weakness during standing and walking.

2. Improved Mobility and Quality of Life

Exercise Performance: 6-minute walking distance increases by 5%–10%, gait speed improves by 4%–8%, stair-climbing time shortens by 10%–15%, and balance (single-leg stance time) enhances by 20%–30%.

Quality of Life: Scores for activities of daily living (e.g., dressing, bathing, shopping) improve by 15%–20%, fall risk decreases by 30%–40%, reducing loss of independence due to sarcopenia.

3. Optimized Metabolic and Health Indicators

It improves insulin resistance in older adults, reducing fasting blood glucose by 5%–8% and increasing muscle glycogen stores by 10%–15%. It also boosts basal metabolic rate, reduces body fat (especially abdominal fat), and lowers the risk of metabolic syndrome associated with sarcopenia.

III. Optimized Intervention Protocols

1. Supplementation Dosage and Methods

Recommended Dosage: 12–20 g daily, divided into 2–3 doses (4–10 g per dose) to avoid gastrointestinal discomfort from single high doses (>15 g).

Timing: Administer within 30 minutes post-exercise (with carbohydrates to enhance absorption) or with meals. Long-term adherence (≥12 weeks) ensures stable effects.

Formulations: Prefer pure L-leucine powders/capsules or complex nutritional supplements containing L-leucine (combined with vitamin D or creatine).

2. Synergistic Intervention Strategies

Nutritional Synergy: Co-supplementation with vitamin D (800–1000 IU/day), calcium (1000–1200 mg/day), and ω-3 fatty acids (1–2 g/day) enhances muscle function improvements by 20%–30%.

Exercise Synergy: Combining with resistance training (2–3 times/week, e.g., dumbbell or resistance band exercises) amplifies L-leucine’s effects by 40%–50%, as resistance training further activates the mTOR pathway, creating nutritional-exercise synergy.

3. Adaptation for Special Populations

Frail Older Adults: Start with 8–10 g/day, gradually increasing to target doses to minimize gastrointestinal irritation.

Older Adults with Hepatic/Renal Insufficiency: Halve the dose (6–10 g/day) and monitor liver/kidney function regularly to ensure safety.

Older Adults with Diabetes and Sarcopenia: Choose sugar-free formulations and monitor blood glucose during supplementation to avoid fluctuations.

IV. Safety and Precautions

1. Safety Profile

Short-term supplementation (≤6 months) at recommended doses shows no significant adverse effects. Gastrointestinal discomfort (bloating, diarrhea) occurs in <5% of cases, mostly due to excessive single doses, and resolves with dosage adjustment. Long-term supplementation (1–2 years) shows no risks of liver/kidney damage or metabolic disorders, confirming good safety.

2. Precautions

Not a Substitute for Balanced Diet: Must be combined with adequate protein (1.2–1.5 g/kg body weight/day), high-quality carbohydrates, and fats to maximize efficacy.

Avoid Excessive BCAA Overlap: If using combined branched-chain amino acid supplements, total leucine intake should not exceed 25 g/day.

Caution in Myopathy Patients: Individuals with muscular dystrophy, etc., should use under medical supervision to avoid increased metabolic burden.