TMG Supplement: The Methyl-Donor Stack with NMN (2026 Science Guide)

If you're researching NMN, you've probably hit a recommendation that almost nobody explains clearly: "take TMG with it."

This guide answers the question behind that recommendation: why does NMN need a methyl donor, what is TMG actually doing, and how much should you take? Short answer first, then the science.

The short answer

TMG (trimethylglycine, also called betaine) is a methyl-donor supplement. When you take NMN, your body uses a process called methylation to clear excess nicotinamide — and that process consumes methyl groups from your cellular pool. Over time, NMN supplementation alone can stress this methyl-donor reserve. TMG replenishes it.

Practically: take 500–1,000 mg of TMG daily, alongside your NMN. That's the dose Dr. David Sinclair publicly takes, and it sits comfortably within the safety range demonstrated in published human trials.^[1]

If you're taking NMN without TMG, you're running one of the most studied longevity compounds with a known biochemical bottleneck unaddressed. That's the gap most NMN-only products leave wide open.

What is TMG?

TMG stands for trimethylglycine. The "tri-methyl" refers to three methyl groups attached to a glycine backbone — three molecular components that your body can detach and use as methylation fuel. The word "betaine" is the older nutritional-science name for the same molecule (TMG and betaine are interchangeable on supplement labels).

You already eat TMG every day. It's naturally concentrated in:

• Beets (where it was first isolated — hence the "betaine" name, from Latin beta)
• Spinach and quinoa
• Wheat germ and whole grains
• Shellfish

Typical dietary intake is roughly 100–500 mg per day, depending on diet. Therapeutic supplementation pushes this into the 500–6,000 mg range, depending on the goal.

What is methylation, and why does it matter?

Methylation is one of the most fundamental processes in cellular biology. A methyl group (a single carbon atom with three hydrogens, written as CH₃) attaches to or detaches from other molecules — DNA, proteins, neurotransmitters, hormones, toxins — and that attachment switches biological functions on or off.

Your body uses methylation for, among many other things:

• DNA repair and gene expression — methylation determines which genes are switched on or off
• Neurotransmitter synthesis — serotonin, dopamine, and norepinephrine all require methylation steps
• Liver detoxification — clearing toxins, hormones, and drug metabolites
• Homocysteine clearance — converting homocysteine (an inflammatory amino acid) back into methionine
• Nicotinamide clearance — which is where NMN supplementation enters the picture

All of these processes draw on a shared cellular pool of methyl donors — primarily SAM (S-adenosylmethionine), the universal methyl donor your body produces from methionine, folate, B12, and choline.

When SAM runs low, every methylation-dependent process slows. Including ones you'd rather have running at full speed.

Why NMN supplementation may deplete methyl groups

Here's the biochemistry. When you take NMN, your body uses it to make NAD+. But the NAD+ system is dynamic — NAD+ is constantly being consumed by sirtuins, PARP enzymes, and the CD38 enzyme, and constantly being regenerated.

One byproduct of all this NAD+ turnover is excess nicotinamide (NAM), the simplest form of vitamin B3. Nicotinamide must be cleared so it doesn't accumulate and inhibit the sirtuin enzymes (which depend on NAD+ for their function).

The clearance enzyme is called NNMT (nicotinamide N-methyltransferase). NNMT takes one methyl group from your SAM pool, attaches it to nicotinamide, and produces methylnicotinamide (which is then excreted in urine).^[4]

The math: every nicotinamide molecule NNMT processes costs one SAM molecule. Multiply that by the volume of nicotinamide cycling through your body when you're taking 500 mg of NMN daily, and you have a sustained, elevated drain on your methyl-donor pool that wouldn't otherwise exist.

The clearer way to say it: NMN doesn't "consume" methyl groups directly. But the nicotinamide turnover NMN causes does — and the higher your NMN intake, the more methyl-donor demand you create.

This is why every serious longevity protocol that includes NMN also includes a methyl donor. TMG is the most common choice because it's cheap, well-studied, and donates methyl groups efficiently.

The evidence: what TMG actually does in humans

TMG has been studied extensively in human clinical trials, mostly under its older name "betaine." The strongest body of evidence is around homocysteine reduction — which is a reliable proxy for whether the methylation cycle is running cleanly.

Key human findings:

• A 2013 meta-analysis of 5 randomized controlled trials found that betaine supplementation (4 g/day for 6–24 weeks) reduced plasma homocysteine by approximately 1.23 μmol/L in healthy adults, about 11.8% from baseline.^[1]
• A 2003 dose-finding trial showed dose-dependent homocysteine reduction with 1.5 g, 3 g, and 6 g betaine daily — reductions of 12%, 15%, and 20% respectively after 6 weeks. The effect was visible from day 1 and sustained throughout the study.^[2]
• A 2023 trial in Chinese adults with elevated homocysteine showed daily 1 g betaine plus low-dose B vitamins for 12 weeks reduced plasma homocysteine by 10.1%.^[3]
• A 2006 acute trial showed 6 g betaine taken before a methionine challenge blunted the resulting homocysteine spike — demonstrating that TMG provides immediate methylation buffering, not just long-term support.^[6]

The evidence pattern is clear: TMG raises methyl-donor availability and clears homocysteine. That's the methylation-support proof of concept.

What TMG does NOT have strong evidence for: high-dose betaine (20 g/day) did not reverse non-alcoholic fatty liver disease in a 12-month randomized trial.^[7] That's important context. TMG's clinical role is methyl-donor and homocysteine support — it is not a treatment for disease, and we don't claim it as one. Anyone selling TMG as a liver "cure" or aging "reversal" is overstating the evidence.

Dosage: how much TMG to take with NMN

The published dose-finding literature uses three main ranges:

Goal	Typical dose	Evidence base
General methyl-donor support / NMN pairing	500–1,000 mg/day	Sinclair's personal protocol; well within published safety
Homocysteine reduction in healthy adults	1,500–3,000 mg/day	Olthof 2003 trial (12–15% homocysteine reduction)
Therapeutic homocysteine reduction (elevated baseline)	3,000–6,000 mg/day	Multiple RCTs in hyperhomocysteinemia populations

For someone supplementing NMN: 500–1,000 mg of TMG once daily is the standard recommendation. Take it at the same time as your NMN. Higher doses aren't necessary unless you have specifically elevated homocysteine levels you're working to bring down — in which case talk to a physician.

Pro tip: take TMG with NMN, not at a separate time. The methyl-donor demand from NMN happens during NMN metabolism. Having TMG circulating at the same time keeps the methylation cycle responsive.

Safety and side effects

TMG has a strong safety profile in published trials. Clinical doses up to 6 g/day for up to 24 weeks have been well-tolerated in healthy adults.^[1][2]

Reported side effects:

• Mild gastrointestinal effects (nausea, loose stools) at high doses — uncommon at 500–1,000 mg/day
• Slight LDL cholesterol increase in some subjects at higher doses (3+ g/day) — small but consistent finding in pooled RCT data^[5]. Another reason 500–1,000 mg is the practical sweet spot for NMN-pairing.
• "Fishy" odor at very high doses — TMG is a precursor to TMAO, which has a fishy smell. Rare at typical supplemental doses.

Talk to a physician before supplementing if you're pregnant, nursing, on blood thinners, or managing a kidney condition. TMG is generally considered safe but every supplement deserves a quick conversation with your healthcare provider before starting.

Why the complete stack matters: TMG is one of five

Here's what most NMN-only protocols miss: even pairing NMN with TMG only addresses two of the four major hallmarks of cellular aging that are clinically actionable through supplementation.

The complete picture:

1. NAD+ decline → restored by NMN
2. Methylation cycle depletion from NMN turnover → restored by TMG (this article)
3. Sirtuin signaling failure → activated by resveratrol. Sirtuins are the NAD+-dependent enzymes that restored NAD+ activates. Without sirtuin activators, you have NAD+ but not full downstream effect.
4. Cellular senescence → cleared by quercetin (a senolytic). Senescent cells consume NAD+ via the CD38 enzyme and pump out inflammation. Clearing them restores tissue NAD+ availability.
5. Oxidative stress → addressed by Green Tea Extract (EGCG). Mitochondria under oxidative load can't use NAD+ efficiently. EGCG also activates AMPK, the cellular energy sensor that complements sirtuin signaling.

This five-compound approach is the multi-pathway logic current longevity research increasingly supports. Pairing NMN with TMG is a critical second step, but stopping there leaves three more known levers untouched.

Nadosei combines all five compounds — NMN, TMG, Resveratrol, Quercetin, and Green Tea Extract — in a single capsule. Manufactured in the USA at an FDA-registered cGMP facility. The complete starter longevity stack, in one bottle.

The bottom line

If you're taking NMN, you almost certainly want TMG with it.

The biochemistry is clear: NMN metabolism elevates nicotinamide turnover, which elevates NNMT activity, which consumes methyl donors. TMG replaces those methyl donors. The published clinical evidence (multiple RCTs, a 2013 meta-analysis, a 2023 trial) shows TMG reliably supports the methylation cycle and clears homocysteine in healthy adults.

500–1,000 mg of TMG daily, taken with your NMN, is the dose that matches both the published safety range and what current longevity protocols recommend. It's what Dr. David Sinclair takes himself.

And the bigger context: a single supplement (even NMN) addresses one pathway. Pairing it with TMG addresses two. The current best evidence in longevity supplementation points toward a multi-compound approach that hits four cellular aging pathways simultaneously — which is exactly the formulation Nadosei was built around.