Amino acids & related compounds

Amino Acids for Healthy Aging

Amino acids and amino-acid–derived compounds are among the better-studied supplement categories for adults over 65 — particularly for muscle preservation, sleep and vascular function. Each entry below carries an evidence grade, the use with the strongest support, typical study dosing, and the cautions that matter most in this age group.

Educational content for adults 65 and older. Supplements interact with common prescriptions including blood thinners, blood-pressure medication, diabetes medication and thyroid replacement. Review anything you plan to take with your physician or pharmacist before starting.

Creatine monohydrate

Strong evidence

Muscle preservation, strength and possibly cognition

Creatine is an amino-acid–derived compound and one of the most studied supplements in existence. In older adults, creatine combined with resistance training consistently produces greater gains in lean mass and strength than training alone.

Best-supported use: Adjunct to resistance training for age-related muscle loss (sarcopenia) and strength maintenance.
Typical dose in studies: 3–5 g daily of creatine monohydrate; no loading phase required.
What the evidence rests on: Multiple meta-analyses of randomised trials in adults over 55 report added lean-mass and upper/lower-body strength benefits when creatine is paired with supervised training.
Cautions and interactions: Raises serum creatinine, which can be mistaken for kidney decline on lab work — tell your clinician you take it. Discuss with your doctor if you have chronic kidney disease. Increase fluid intake.

Glycine

Moderate evidence

Sleep quality, collagen synthesis, glutathione support

A cheap, well-tolerated conditionally essential amino acid. The best evidence is small randomised trials showing improved subjective sleep quality and next-day alertness when taken before bed.

Best-supported use: Sleep quality in people with mild, non-clinical sleep complaints.
Typical dose in studies: 3 g taken roughly 60 minutes before bed in the published sleep trials.
What the evidence rests on: Small placebo-controlled crossover trials (Japanese sleep research group) plus mechanistic work on glycine's role in glutathione and collagen synthesis.
Cautions and interactions: Generally well tolerated. Sleep trials are small and short; glycine is not a treatment for insomnia or sleep apnoea. Can interact with clozapine.

Taurine

Mixed evidence

Cardiometabolic markers; heavily hyped as a longevity molecule

Taurine declines with age and reversing that decline extended lifespan in mice — a widely reported 2023 finding. Human data are far thinner: modest blood-pressure and glycaemic effects in small trials, with no lifespan evidence in people.

Best-supported use: Small reductions in blood pressure and some metabolic markers in short trials; the longevity claim is not established in humans.
Typical dose in studies: 1–3 g daily in most human trials.
What the evidence rests on: Meta-analyses of small blood-pressure trials show modest reductions; the lifespan work is animal-only and should be read as hypothesis-generating.
Cautions and interactions: Good short-term safety record, but long-term high-dose data in older adults are lacking. Not a substitute for antihypertensive therapy.

L-citrulline

Moderate evidence

Blood flow, blood pressure, walking performance

Citrulline raises plasma arginine more efficiently than arginine itself and supports nitric-oxide production. Trials in older adults show modest improvements in blood pressure and vascular function.

Best-supported use: Modest blood-pressure and endothelial-function improvements.
Typical dose in studies: 3–6 g daily of L-citrulline (or 8 g citrulline malate in exercise studies).
What the evidence rests on: Meta-analyses of randomised trials report small but statistically significant systolic and diastolic reductions.
Cautions and interactions: Additive with nitrates and blood-pressure medication — check with your clinician. Avoid combining with PDE5 inhibitors without medical advice.

L-arginine

Mixed evidence

Nitric oxide and vascular function, but poor oral bioavailability

The direct nitric-oxide precursor, but extensive first-pass metabolism limits how much oral arginine reaches circulation. Citrulline usually raises arginine levels more reliably.

Best-supported use: Small blood-pressure reductions in some trials; results are inconsistent across populations.
Typical dose in studies: Trials commonly use 4–6 g daily, often split.
What the evidence rests on: Mixed randomised-trial results; the post-infarction safety signal is the most important finding for older adults.
Cautions and interactions: Gastrointestinal upset is common at higher doses. Caution after myocardial infarction — one trial in post-MI patients reported worse outcomes. Discuss with a cardiologist before use.

N-acetylcysteine (NAC)

Mixed evidence

Glutathione precursor; established clinical uses, speculative aging uses

NAC has genuine clinical roles (paracetamol overdose, mucus clearance in some lung disease). Its popular use as an antioxidant or anti-aging agent rests on much weaker evidence.

Best-supported use: Mucolytic use in chronic bronchitis/COPD and hospital antidote use; general healthy-aging benefit is unproven.
Typical dose in studies: 600–1,200 mg daily in the respiratory trials.
What the evidence rests on: Cochrane-level support for mucolytic use; healthy-aging and cognition claims come from small or preclinical studies.
Cautions and interactions: May potentiate nitroglycerin and some blood thinners. Regulatory status has fluctuated in the US. Discuss with your pharmacist if you take cardiac or anticoagulant medication.

Leucine & HMB

Moderate evidence

Anabolic resistance and muscle preservation after 65

Older muscle responds less strongly to protein — 'anabolic resistance'. Leucine-enriched protein, and its metabolite HMB, are studied specifically to overcome that, especially during illness or bed rest.

Best-supported use: Preserving lean mass in older adults during immobilisation, hospital stays or low protein intake.
Typical dose in studies: Roughly 2.5–3 g leucine per meal within a 25–40 g protein dose; HMB trials commonly use 3 g daily.
What the evidence rests on: Meta-analyses show HMB helps preserve lean mass in older adults during periods of disuse, with smaller effects in healthy, active seniors.
Cautions and interactions: Whole-food protein comes first — isolated amino acids do not replace adequate total protein. Discuss with a clinician if you have kidney disease.

L-glutamine

Limited evidence

Gut and immune claims common in marketing; weak general evidence

Glutamine is important in critical illness and specific clinical settings. For healthy older adults, the gut-healing and immune claims are largely extrapolated beyond the evidence.

Best-supported use: Specific clinical nutrition settings under medical supervision.
Typical dose in studies: 5–10 g daily in consumer products; clinical dosing differs and is supervised.
What the evidence rests on: Clinical-nutrition trials in illness; little quality evidence for routine use in healthy aging.
Cautions and interactions: Caution with liver disease or a history of seizures. Discuss with your clinician.

How we grade evidence

Strong — consistent findings across multiple randomised trials or meta-analyses, including studies in older adults.
Moderate — several randomised trials pointing the same direction, with limitations in size, duration or population.
Mixed — trials disagree, or benefits appear only in specific subgroups.
Limited — small, short, preliminary or largely preclinical evidence.

Compounds with early-stage evidence only are covered separately in Emerging Research.