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Walk into any longevity supplement conversation, and you will hear at least five different names — Ca-AKG, AAKG, OAKG, Na-AKG, Mg-AKG. Most of them share the same active molecule. Not all of them share the same evidence base.
This guide covers every commercially sold AKG form, with each one tier-graded by how much human evidence actually supports it. For the wider Ca-AKG evidence picture, see our pillar: calcium alpha-ketoglutarate — the complete evidence-based guide. Every citation links back to a paper page in our Ca-AKG Data Center.
Why does AKG come in so many forms?
Alpha-ketoglutarate is a small carboxylic acid — chemically reactive, hygroscopic (it absorbs water from the air), and unstable in bulk powder form. Left as free acid, it degrades over time and is unpleasant to handle. So supplement manufacturers bind it to a partner molecule as a stable salt.
What the partner molecule is changes three things: shelf stability, gastric survival, and what else the compound delivers alongside the AKG. Calcium adds elemental calcium. Arginine adds an amino acid that raises nitric oxide. Ornithine adds an amino acid used in ammonia detoxification. Sodium adds sodium — nothing biologically remarkable at typical doses. Magnesium adds magnesium. Creatine adds creatine.
The catch: adding a partner molecule doesn't automatically create a compound with a research base. Most of the AKG forms currently on the market have essentially no clinical evidence behind them. Only three forms — Ca-AKG, AAKG, and OAKG — have any meaningful peer-reviewed human data at all.
All seven AKG forms at a glance
| Form | Full name | Partner molecule | Primary use case | Human evidence tier |
|---|---|---|---|---|
| Ca-AKG | Calcium alpha-ketoglutarate | Calcium (mineral) | Longevity, healthy ageing, biological age | Tier 2 — growing human data |
| Delayed-release Ca-AKG | Ca-AKG in delayed-release capsule | Same as Ca-AKG | Longevity (proprietary Rejuvant formulation) | Tier 2 — largest human effect signal |
| AAKG | Arginine alpha-ketoglutarate | L-arginine (amino acid) | Exercise performance, muscle pump | Tier 3 — heterogeneous, biased signal |
| OAKG | Ornithine alpha-ketoglutarate | L-ornithine (amino acid) | Surgical recovery, burn care, protein metabolism | Tier 2 — decades of clinical use |
| Na-AKG | Sodium alpha-ketoglutarate | Sodium (mineral) | Alternative to Ca-AKG (avoids calcium load) | Tier 3 — limited direct data |
| Mg-AKG | Magnesium alpha-ketoglutarate | Magnesium (mineral) | General health (marketing) | Tier 4 — essentially no human data |
| Creatine AKG | Creatine alpha-ketoglutarate | Creatine (amino acid derivative) | Sports performance (marketing) | Tier 4 — essentially no human data |
The two forms with genuine longevity evidence are Ca-AKG and its delayed-release variant. The form with the deepest clinical safety record is OAKG. Everything else is either marketing-led or specialised for a narrow use case.
Ca-AKG — calcium alpha-ketoglutarate
The dominant form on the longevity supplement market. Alpha-ketoglutarate bound to a calcium ion as a stable salt. A typical 1 g dose delivers roughly 200 mg of elemental calcium alongside the active AKG.
This is the form the modern longevity conversation is built on. The 2020 Cell Metabolism mouse study at the Buck Institute used food-incorporated Ca-AKG and found extended lifespan and compressed frailty in middle-aged mice [2]. The 2021 Rejuvant retrospective in Aging used Ca-AKG in a delayed-release capsule [3]. The ABLE randomised trial protocol tests Ca-AKG. The Chinese trial NCT07114536 tests Ca-AKG. Every longevity study that matters used this specific form.
The calcium partner is a delivery vehicle. It stabilises the molecule for capsule storage and helps it survive the acidic environment of the stomach. Once absorbed, calcium and AKG go their separate ways. For the fuller mechanistic walkthrough, see how Ca-AKG works. For the "is Ca-AKG the same as free AKG" question specifically, see Ca-AKG vs free AKG.
Practical positioning: this is the default choice for anyone interested in AKG for longevity or healthy ageing. Widely available, moderate price, evidence-backed to the extent any AKG form currently is.
Delayed-release Ca-AKG — a formulation, not a chemical form
Worth calling out separately because it is almost universally confused with a different chemical form. It is not. Delayed-release Ca-AKG is the same calcium salt as standard Ca-AKG. What differs is the capsule technology — a coating or matrix that holds the compound intact until it reaches the lower small intestine, releasing it gradually rather than dumping it in the stomach.
This distinction matters because in the 4,260-person Pabis 2026 Aging Cell cohort, delayed-release Ca-AKG (Rejuvant formulation) was associated with a biological age approximately 1.8 years lower than expected. Standard immediate-release Ca-AKG showed an effect roughly 8 times smaller and did not reach statistical significance [4].
Read that as: the formulation appears to matter more than most retailers acknowledge. Same chemical form, different capsule, meaningfully different effect signal in the largest available dataset.
The Rejuvant formulation is proprietary and premium-priced. Whether the delayed-release advantage holds up in the randomised trials reading out in 2026 is the question that will settle this comparison.
AAKG — arginine alpha-ketoglutarate
Alpha-ketoglutarate bound to L-arginine, marketed almost exclusively to bodybuilders and endurance athletes. The commercial pitch: L-arginine feeds nitric oxide production, nitric oxide dilates blood vessels, better blood flow improves exercise performance.
The evidence is more equivocal than the marketing implies. The most-cited pooled analysis is a 2020 systematic review and meta-analysis in Nutrients covering 15 randomised trials of arginine supplementation in various forms including AAKG [7]. The headline result was a large positive effect on aerobic performance (Hedges' g = 0.84) and a small positive effect on anaerobic performance (g = 0.24) — but with 89% between-study heterogeneity for the aerobic outcome and statistically significant publication bias flagged by the authors' own funnel plot. A 2025 formal comment in the same journal documented methodological errors that the authors partially acknowledged.
Beyond the meta-analytic caveats, orally administered L-arginine has poor bioavailability because of first-pass metabolism by the intestinal enzyme arginase — one of the reasons the sports supplement market has been shifting from arginine-based to citrulline-based formulations for over a decade.
Practical positioning: AAKG has no longevity data, and the peer-reviewed exercise evidence is weaker than the marketing suggests. Not a substitute for Ca-AKG for longevity, not the best-evidenced choice for exercise. For the full disambiguation, see Ca-AKG vs AAKG.
OAKG — ornithine alpha-ketoglutarate
The form with the deepest legitimate clinical history, and the one most under-represented in the longevity supplement conversation.
OAKG has been used in mainstream clinical medicine for decades — as a post-surgical recovery agent, in burn care, in the management of protein-calorie malnutrition, and in the treatment of hepatic encephalopathy. The mechanism is different from Ca-AKG's longevity biology. OAKG's therapeutic effects come primarily from its role in ammonia detoxification and nitrogen balance, which matters for patients recovering from major tissue injury or with impaired liver function. The 2017 review in Archivum Immunologiae et Therapiae Experimentalis catalogues this clinical history in detail [1].
OAKG has essentially no longevity data. It has never been positioned as a healthy-ageing supplement — its clinical development track has always been surgical recovery and metabolic medicine. This is why it rarely appears in longevity supplement stacks despite having the deepest safety record of any AKG form.
Practical positioning: not relevant for someone looking for a longevity supplement. Highly relevant if a doctor has recommended it in a clinical recovery context.
Sodium AKG (Na-AKG)
Alpha-ketoglutarate bound to sodium instead of calcium. Structurally analogous to Ca-AKG — a stable salt of AKG paired with a common mineral — but adding sodium rather than calcium to the delivery package.
The 2020 Cell Metabolism mouse study actually used sodium AKG in its in vitro senescence-associated secretory phenotype (SASP) experiments, though the in vivo mouse lifespan work used calcium AKG in food [2]. The 2014 Nature work in nematodes used sodium AKG dissolved in feeding media [6]. So Na-AKG has mechanistic and preclinical data — it just does not have direct human trial data of its own.
Practical positioning: a legitimate alternative to Ca-AKG for anyone who wants to avoid the calcium load. Lower cost per gram than Ca-AKG. Not as widely available. No human longevity trials. Sodium content is trivial at typical AKG doses.
Magnesium AKG (Mg-AKG) and creatine AKG — the evidence gaps
Both are on the market. Both have essentially no peer-reviewed human evidence.
Mg-AKG. Marketed as "AKG plus magnesium" with the pitch that magnesium supports muscle and nervous system function. This is true of magnesium generally — but no peer-reviewed human trial has demonstrated that Mg-AKG produces effects distinct from taking Ca-AKG and a separate magnesium supplement. The 2022 Trends in Endocrinology and Metabolism review of the human AKG literature does not include Mg-AKG as a distinct evidence category [5].
Creatine AKG. Marketed as "AKG plus creatine" for sports performance. Two small trials have tested it against creatine monohydrate for strength and endurance outcomes, with essentially null results. The 2017 pleiotropic review does not treat creatine AKG as a distinct clinical category [1]. There is no longevity data.
Practical positioning: neither form has an evidence base to justify choosing it over a better-studied alternative. If you want AKG for longevity, Ca-AKG. If you want magnesium, take magnesium (glycinate or citrate). If you want creatine, take creatine monohydrate — the most-studied ergogenic supplement in existence.
Which form should you actually take?
Match the form to the actual goal.
Longevity, healthy ageing, biological age. Delayed-release Ca-AKG has the largest human effect signal. Standard Ca-AKG is the defensible middle-ground choice. Neither AAKG nor OAKG nor the other forms are evidence-appropriate substitutes.
Exercise performance and muscle pump. AAKG is one option, but the evidence is heterogeneous, and the market has been shifting to citrulline-based products. Not a strong pick.
Post-surgical or clinical recovery. OAKG under medical supervision. This is a clinical decision, not a supplement decision.
Avoiding the calcium load. Sodium AKG or free AKG powder. Both give you the alpha-ketoglutarate without the elemental calcium of Ca-AKG.
Avoiding the arginine load. Any AKG form other than AAKG.
For the dose-picking question across all forms, see Ca-AKG dosage: what the trial data supports. For the safety walkthrough, see Ca-AKG side effects and safety profile. For a physician-authored buyer's guide to what is actually on the UK and US market, see the best Ca-AKG supplement guide. And if you are still not sure whether you want Ca-AKG or free AKG, what is Ca-AKG covers the basic disambiguation in plain English.
Bottom line
Seven AKG forms are commercially sold. Only three — Ca-AKG (including its delayed-release variant), AAKG, and OAKG — have peer-reviewed human evidence of any kind. Only Ca-AKG and its delayed-release variant have longevity evidence. Only OAKG has decades of clinical safety data in a medical context.
For the longevity use case that drives most of the consumer interest in AKG, the choice is between standard Ca-AKG (defensible, widely available, moderate cost) and delayed-release Ca-AKG (strongest human signal in the largest cohort, premium price). Everything else is either marketing-led, misdirected from the wrong sub-market, or a clinical form that should not be self-prescribed.
For the full evidence walkthrough on Ca-AKG specifically, see the Ca-AKG pillar.