AKG forms explained: Ca-AKG, AAKG, OAKG, and the rest

“AKG” is not one supplement formulation. Alpha-ketoglutarate appears as a free acid and as salts paired with calcium, arginine, ornithine, sodium and other partners. Those products all connect to AKG biology, but they do not have interchangeable doses, pharmacology or evidence.

The most important rule is simple: follow the exact form used in the study behind the claim. A result from Ca-AKG does not automatically belong to AAKG, OAKG or free alpha-ketoglutaric acid.

AKG forms at a glance

Form	Partner	What human evidence exists?	What it does not establish
Ca-AKG	Calcium	Acute human metabolic exposure, bone RCT, historical renal studies, modern aging research	Proven human longevity
Delayed-/controlled-release Ca-AKG	Calcium; different delivery system	Rejuvant observational biological-age studies; ABLE randomized protocol	Randomized superiority over standard Ca-AKG
Free AKG / alpha-ketoglutaric acid	None	Human oral pharmacokinetic work at high doses	Human longevity efficacy
AAKG	L-arginine	Direct exercise studies and broader arginine meta-analysis	Ca-AKG longevity effects
OAKG	L-ornithine	Human kinetics and clinical nutrition/burn studies	Healthy-aging efficacy
Na-AKG	Sodium	Mainly mechanistic/preclinical AKG evidence	Direct human longevity efficacy
Mg-AKG / creatine-AKG and other niche salts	Magnesium, creatine, etc.	Much thinner form-specific evidence in the audited Ca-AKG corpus	Equivalence to better-studied forms

Ca-AKG: the calcium salt

Calcium alpha-ketoglutarate is the dominant form in the modern longevity conversation.

A small 1990 human study administered 3.6 g of Ca-AKG and showed measurable changes in circulating metabolites, confirming that oral Ca-AKG is biologically active [1].

The 2007 randomized osteopenia trial used Ca-AKG and found a larger reduction in the bone-resorption marker CTX than calcium alone [2].

The 2020 mouse healthspan/lifespan study also used Ca-AKG in chow [3].

That makes Ca-AKG the form with the clearest continuity between historical human exposure, the key mouse aging study and modern longevity research.

It still has not been shown to extend human lifespan.

Delayed-release Ca-AKG is a formulation, not a different chemical salt

Delayed- or controlled-release Ca-AKG uses the same underlying calcium salt with a delivery system intended to alter where or how quickly it is released.

The 2021 Rejuvant retrospective used a sustained-release Ca-AKG product with added vitamins [4].

In the 2026 Pabis cohort, users of delayed-release AKG had a significant cross-sectional association with lower DNA-methylation Age Residual, while plain non-delayed AKG showed a smaller, non-significant association [5].

That study was observational, not a randomized head-to-head formulation trial. The delayed-release product also contained vitamins, and the adjusted longitudinal signal was not significant. It therefore cannot establish a precise superiority ratio or prove that release kinetics caused the difference.

ABLE tests 1 g/day sustained-release Ca-AKG against placebo, but published efficacy results are not yet present in our audited corpus [6].

Free AKG: human absorption exists, longevity evidence does not

Free alpha-ketoglutaric acid is often described online as if nobody has ever given it orally to humans. That is incorrect.

A 2010 healthy-volunteer study tested single or split oral free-AKG doses from 5 to 20 g in an antidote-development context [7].

Absorption depended on dose and administration conditions. Splitting a 20 g total dose improved estimated bioavailability compared with taking all 20 g at once, and water intake affected apparent absorption.

Those doses are far above ordinary longevity-supplement use, and the study did not compare free AKG head-to-head with Ca-AKG.

So two common claims are both too strong:

• “Free AKG is not absorbed” — false; human oral absorption has been studied.
• “Ca-AKG is proven more bioavailable than free AKG” — not established by a direct human comparison.

AAKG: arginine alpha-ketoglutarate

AAKG combines AKG with L-arginine and belongs primarily to the sports-nutrition literature.

An eight-week randomized study in trained men used 12 g/day AAKG and reported improvements in bench-press 1RM and Wingate peak power, with no significant benefit for body composition, aerobic capacity or isokinetic endurance [8].

A later acute study using 3 g AAKG found no improvement in strength, repetitions to failure or total load volume [9].

A 2020 meta-analysis of arginine supplementation reported positive pooled performance effects, but it mixed L-arginine, arginine aspartate and AAKG, had very high heterogeneity for aerobic performance and showed publication-bias concerns [10].

AAKG therefore has human exercise evidence. It does not have Ca-AKG's longevity evidence.

OAKG: ornithine alpha-ketoglutarate

OAKG has a substantial clinical-nutrition history that should not be confused with longevity research.

Human kinetic work shows that oral OAKG is rapidly metabolized and changes amino-acid, insulin and glucose profiles [11].

In a randomized trial in severe burn patients, 20 g/day OAKG for three weeks shortened wound-healing time versus an isonitrogenous control and was reported as well tolerated in that specialized clinical setting [12].

This is meaningful human evidence for OAKG. It does not make OAKG a human longevity supplement.

Sodium AKG and other mineral salts

Sodium AKG appears in mechanistic and preclinical AKG research, but direct human longevity evidence is lacking.

Magnesium-AKG, creatine-AKG and other niche forms may be commercially available, but a product existing does not establish that the combined salt has clinically demonstrated advantages over taking the better-studied components separately.

For any niche form, ask for a form-specific trial rather than importing evidence from Ca-AKG or from the partner nutrient.

Why the label milligrams can be misleading

A label may report:

• the mass of the entire AKG salt;
• the AKG component alone;
• the partner mineral separately;
• or a proprietary blend amount.

Those numbers are not automatically comparable.

For example, 1,000 mg of a calcium salt is not necessarily 1,000 mg of AKG base. This is why product comparisons need to state what the label figure actually represents.

Which form has the strongest longevity evidence?

The aging literature is concentrated around Ca-AKG and the proprietary delayed-release Ca-AKG formulation.

That is an evidence-matching statement, not proof that Ca-AKG is chemically or clinically superior to every other form.

Free AKG has human pharmacokinetic data but not a longevity efficacy trial. AAKG has exercise studies. OAKG has clinical-nutrition studies. Each form should be judged against its own evidence rather than one shared “AKG” bucket.

Bottom line

There is no single universal “AKG form.”

Ca-AKG has the strongest direct connection to the modern longevity literature. Delayed-release Ca-AKG is a delivery variant with observational biological-age data, not a separate molecule. Free AKG has human oral pharmacokinetic evidence but no human longevity efficacy data. AAKG and OAKG have their own distinct human research histories.

The most reliable rule is: match the form on the label to the form in the study behind the claim.

For the calcium-salt versus free-acid question specifically, see Ca-AKG vs AKG. For the arginine salt, see Ca-AKG vs AAKG.