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In May 2026, a peer-reviewed study by Tretowicz and colleagues, published in Nature Metabolism, reported that whole-blood NAD+ levels don't reliably decline with age. Not long after, The New York Times ran a piece asking whether the case for NAD+ supplements still holds up.
So here is an honest look at what the study found, what it leaves open, and how we think about NR in light of it. Some of this is settled. Some of it science is still working out. We'd rather tell you which is which.
What the Nature Metabolism Study Found
The study measured whole-blood NAD+ across seven cohorts and more than 300 people. Its central finding was that whole-blood NAD+ does not reliably decline with age, and that common lifestyle changes like diet and exercise don't move it much.
This is a careful, well-run study, and we take it seriously. It sharpens a question researchers have been circling for years: what does a blood NAD+ measurement actually tell us?
The Honest Open Question About Blood NAD+
Science does not yet have a complete answer for what blood NAD+ reflects about NAD+ inside the tissues where it does much of its work, like muscle, brain, and liver.
Part of the reason is practical. Measuring NAD+ directly in human tissue is difficult. It generally means numbing and biopsying the tissue, and a muscle biopsy in particular is no small thing to ask of a study volunteer. Blood is easy to draw, which is part of why it gets measured so often. Easy to measure and most informative are not always the same thing.
None of that makes the Tretowicz finding less valid. It makes it a useful prompt to ask sharper questions, which is how science is supposed to move.
Our Chief Scientific Advisor, Dr. Charles Brenner, Ph.D., who first characterized NR's role as an NAD+ precursor, has been consistent on this for years:
"We've never said that blood NAD+ declines in aging or thought that blood is the key target tissue for NR.” — Charles Brenner, Ph.D.
Does This Outcome Impact the Use of NAD+ Precursors?
A lot of the conversation around this study cast doubt on NAD+ supplementation broadly, lumping NR, NMN, and NAD+ together rather than weighing each on its own merits. The differences are worth understanding if you're deciding what to take. First, let’s explain why NAD+ precursors matter. A precursor is a building block your body uses to make important molecules. For example, amino acids are the building blocks of proteins. Certain forms of vitamin B3 (niacin) serve as precursors to NAD+, helping your cells produce it. NAD+ is essential for cellular energy production (ATP) as well as cellular defense and repair, making these precursors an important part of the process. But they’re not created equal:
NAD+ is a coenzyme found in every cell and is needed to make cellular energy. Taken orally or by IV/injection, NAD+ itself can't enter cells directly because it’s too large to cross the cell membrane.
NMN (nicotinamide mononucleotide) is often described as one step closer to NAD+, which is true inside the cell. As an oral supplement, though, it contains a phosphate that must be removed before it can cross the cell membrane. Removing this phosphate creates NR that crosses the cell membrane directly and is converted to NAD+ in 2 steps. So that "one step closer" framing doesn't carry the advantage it sounds like it should.
NR (nicotinamide riboside) is a form of vitamin B3 the body uses to make NAD+. Taken orally, it raises NAD+ efficiently and is well tolerated, without the flushing that high-dose niacin can cause. It's the form used in more than 75% of published human studies on nicotinamide riboside, and Niagen NR has been studied in over 45 peer-reviewed human studies.
NR also has an established regulatory and quality profile in the U.S., including GRAS status and Niagen Bioscience worked with the U.S. Pharmacopeia to develop a USP monograph for nicotinamide riboside chloride that becomes official in October 2026.
The differences between these three molecules are chemical and biological, with real implications when you supplement.
Research on NR Beyond Blood NAD+
The research on NR covers more than blood NAD+ levels alone.
A 2024 study (Nanga et al., Magnetic Resonance in Medicine) used imaging to measure NAD+ in the brain. A single dose of NR raised cerebral NAD+ in healthy volunteers.
A 2023 study (Lapatto et al., Science Advances) followed adult twin pairs across a range of body weights over five months. NR increased muscle mitochondrial biogenesis, the building of new mitochondria, and positively shifted gut microbiome composition.
What This Means If You Take Tru Niagen
The science of NAD+ is still developing, and that shapes how researchers read a study like this one. What a blood NAD+ measurement tells us, and how it relates to NAD+ inside tissues, is genuinely still an open question. Careful studies like Tretowicz et al. help refine it.
What's clearer is the research on NR itself. Across human studies, NR has been clinically shown to support cellular NAD+ levels and mitochondrial function, with effects that reach beyond a single blood reading. That body of evidence is why people continue taking it, and why many healthcare professionals continue to recommend it.
One thing we'll always be straight about: NAD+ support complements the fundamentals of healthy aging. It belongs alongside sleep, movement, and good nutrition, not in place of them.
We'll keep following the science wherever it leads, contributing to it where we can, and we'll keep walking through the results with you, including the parts that are still unresolved.
For our science team's full analysis of the blood NAD+ question, read the Niagen Bioscience white paper: Whole Blood NAD+ and Aging.
For further reading on NAD+ decline with age in blood and tissue from an evidence-based scientific research standpoint, visit AboutNAD: Does NAD+ Decline with Age? Blood and Tissue Data Tell Different Stories.