Written by the Nuvirox Research Team
Key points
- The concern is real biochemistry: clearing excess nicotinamide requires methylation by NNMT, which spends S-adenosylmethionine (SAM), the body’s universal methyl donor.
- The one human trial that actually measured it found no change. In NADPARK, 1,000 mg of nicotinamide riboside daily for 30 days raised methylated nicotinamide metabolites sharply but left SAM, SAH and homocysteine unchanged.
- That is reassuring for typical doses over a month. It is not evidence about very high doses, long durations, or people with unusual one-carbon metabolism.
Short answer: the methyl-depletion argument is biochemically coherent, and the only human trial that directly measured methylation markers found no depletion at 1,000 mg of NR per day for 30 days. That does not make the concern stupid — it makes it unconfirmed. If you have been told you must take TMG with your NAD+ precursor, the honest position is that the requirement has not been demonstrated in people.
Where does the methyl-depletion worry come from?
It comes from following the exit route. NAD+ precursors raise the NAD metabolome, and one consequence is more nicotinamide passing through. The body disposes of surplus nicotinamide by methylating it, using the enzyme nicotinamide N-methyltransferase (NNMT), producing methylnicotinamide and then its oxidised derivatives, which are excreted in urine.
Every one of those methylations spends a methyl group from SAM. SAM is also the donor for DNA and histone methylation, phospholipid synthesis and neurotransmitter production. Using SAM generates S-adenosylhomocysteine (SAH), which is broken down to homocysteine. So in principle, driving nicotinamide clearance harder could compete for methyl groups and raise homocysteine.
What did the trial that actually measured it find?
The NADPARK study is the key document here, because it did not just theorise about methylation — it measured the relevant metabolites.
Study snapshot
| Design | Double-blinded, randomised, placebo-controlled phase I |
| Population | 30 newly diagnosed, dopaminergic-therapy-naive Parkinson’s patients |
| Dose | 1,000 mg nicotinamide riboside daily |
| Duration | 30 days |
| Methylation finding | Methylated nicotinamide metabolites (MeNAM, Me-2-PY, Me-4-PY) rose substantially in blood, muscle and CSF. SAM, SAH and homocysteine showed no significant change. |
| Registration | ClinicalTrials.gov NCT03816020 |
The authors’ own reading was direct: the absence of change in SAM and its related metabolites indicated that NR supplementation did not limit SAM availability for other essential reactions. A companion analysis of the same trial material extended this to genome-wide DNA methylation and again found no effect, including when participants were stratified by MTHFR genotype — the variant most often invoked as the reason to worry.
What human studies actually show — including the limits
The direct measurement is negative. That is the strongest single piece of evidence available, and it points against clinically meaningful methyl depletion at 1,000 mg NR for a month.
Different B3 forms behave differently. Nicotinamide and nicotinic acid are not interchangeable on this axis. Published comparisons have found nicotinamide raising homocysteine more than nicotinic acid does, and lowering plasma betaine more strongly. So the concern is not evenly distributed across everything labelled vitamin B3, and evidence about one form does not automatically transfer to another.
The honest counterweight: 30 days at one dose in 30 people with one disease is a narrow evidence base. The NADPARK investigators themselves flagged that it remains unknown whether such effects occur at higher NR doses. Subsequent dose-optimisation protocols were written specifically to test methylation metabolism across a dose range, which is a fair signal that the field does not consider the question closed. Anyone telling you the matter is definitively settled — in either direction — is going beyond the data.
So should you take TMG with an NAD+ precursor?
The honest answer is that there is no human trial showing you need to, and no human trial showing it improves any outcome when combined with NR or NMN. TMG (trimethylglycine, or betaine) is a legitimate methyl donor found in beets, spinach and whole grains, and it is not a dangerous compound. But co-supplementing it is currently a precaution against a theoretical problem rather than a correction of a demonstrated one.
Two practical points do follow from the biochemistry. First, adequate folate, B12 and choline status supports one-carbon metabolism generally, and that is worth having regardless of what else you take. Second, if you are on very high doses of plain nicotinamide — well above what NAD+ trials use — the methylation load argument becomes more relevant than it is at standard precursor doses.
| Scenario | Strength of the methyl-load concern |
|---|---|
| NR or NMN at typical trial doses (250–1,000 mg/day) | Low — directly measured and not observed |
| High-dose plain nicotinamide (multi-gram) | Higher — more nicotinamide requiring methylated clearance |
| Long-term use beyond studied durations | Unknown — no data either way |
| Known B12, folate or one-carbon disorder | Discuss with your clinician rather than self-manage |
What this analysis won’t settle
It will not tell you about multi-year use, because nobody has measured that. It will not cover doses well above 1,000 mg. And it does not address the separate question of side effects generally, which we handle in nicotinamide riboside side effects. If you want the mechanistic background on why nicotinamide accumulates in the first place, start with the NAD+ salvage pathway, and for how the different precursors compare, NR vs. NMN vs. NAD+.
Frequently asked questions
Does NR raise homocysteine?
In the one trial that measured it directly — 1,000 mg daily for 30 days — no significant change in homocysteine was observed. Published comparisons of B3 forms suggest plain nicotinamide has a stronger effect on homocysteine than nicotinic acid, so the form matters.
Do I need TMG with NMN specifically?
The same reasoning applies: NMN also increases nicotinamide flux and therefore methylated clearance products. But the human methylation data comes from NR trials, and no trial has shown that adding TMG to either precursor changes an outcome.
What about the MTHFR variant everyone mentions?
A companion analysis of the NADPARK material examined DNA methylation stratified by MTHFR genotype and found no effect of NR on global methylation levels or distribution. That is the most relevant human data available on this specific worry.
Is TMG harmful to take anyway?
TMG is a normal dietary component and is generally well tolerated. The argument here is not that it is risky, only that the case for needing it alongside an NAD+ precursor is currently theoretical rather than demonstrated.
Could methyl depletion show up only after months?
Possibly, and this is the fairest version of the concern. The direct human measurement covered 30 days. Longer-duration data does not exist, so the honest answer is that nobody knows.
From Nuvirox
Why we formulated NAD+ Restore.
NAD+ Restore uses 500 mg of nicotinamide riboside chloride — within the range used in published human trials, and below the 1,000 mg dose at which methylation markers were directly measured and found unchanged.
- 500 mg Nicotinamide Riboside Chloride (NR) — one of the two most-researched NAD+ precursors, within the dose range used in published human trials.
- 150 mg trans-resveratrol (Japanese Knotweed) + 50 mg quercetin (Sophora japonica) — polyphenols studied alongside NAD+ pathways for cellular health support.
- 10 mg galactomannans from fenugreek — to support absorption.
- 60-day money-back guarantee — long enough to actually evaluate it the way the research says you should.
The bottom line
The methyl-depletion argument deserves better than either dismissal or panic. It is grounded in real biochemistry: clearing nicotinamide costs methyl groups. But when researchers actually measured SAM, SAH, homocysteine and genome-wide DNA methylation in people taking 1,000 mg of NR daily for a month, nothing moved. That is the best human evidence available, and it points away from the concern at typical doses over typical durations. What it cannot tell you is what happens at higher doses or over years, and the researchers running the follow-up dose-ranging studies clearly agree that gap is worth closing. Take TMG if you want to; just know you are buying reassurance, not a demonstrated correction.
References
- Brakedal B, Dölle C, Riemer F, et al. The NADPARK study: a randomized phase I trial of nicotinamide riboside supplementation in Parkinson’s disease. Cell Metabolism. 2022;34(3):396-407.e6. PMID: 35235774. DOI: 10.1016/j.cmet.2022.02.001. ClinicalTrials.gov: NCT03816020.
- Nicotinamide N-methyltransferase (NNMT): a novel therapeutic target for metabolic syndrome. PMCID: PMC11196770.
- Conze D, Brenner C, et al. What is really known about the effects of nicotinamide riboside supplementation in humans. PMID: 37478182.
- Yaku K, Okabe K, Nakagawa T. NAD metabolism: implications in aging and longevity. Reviewed in: Yoshino M, et al. Nicotinamide phosphoribosyltransferase as a key molecule of the aging/senescence process. International Journal of Molecular Sciences. PMCID: PMC8037941.
- Redzic S, Hashmi MF, Gupta V. Niacin deficiency. StatPearls. NCBI Bookshelf ID: NBK557728.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and is not a substitute for professional medical advice.