Researchers at Vilnius University Life Sciences Center have challenged a core assumption behind the nicotinamide adenine dinucleotide (NAD, often referred to in its oxidised form as NAD+) supplements boom with the publication of a new study.
Their study — using more than 1000 people and published in Nature Metabolism — found that blood NAD levels did not decline with age in healthy participants.
Levels stayed stable in men and, unexpectedly, rose in women.
The team also found lower NAD levels in people with cardiovascular disease, particularly hypertension.
It remains unclear whether low NAD contributes to disease or results from it, with lead researcher Dr Dalius Ratautas saying the results show how much is still unknown about NAD biology.
A second study points the same way
The Vilnius findings have not appeared in isolation — a separate Nature Metabolism paper from Amsterdam UMC found whole-blood NAD+ levels remained stable with age and across lifestyle interventions, but changed in response to nicotinamide riboside supplementation.
However, experts urge caution when interpreting the findings.
Whole-blood NAD+ does not reflect tissue-specific changes, such as those seen in ageing muscle. Some earlier studies have observed an inverse association between age and blood NAD+.
The tissue question remains open and answering it would require muscle biopsies and more advanced imaging rather than simple blood draws.
Pressure on longevity messaging
The studies land as demand for NAD-related products continues to climb. Reports suggest robust category growth, with a projected 29.3% rate in 2026.
Yet the supplement's narrative is under scrutiny, with one researcher quoted by The New York Times (via The Nightly) saying consumer messaging on NAD+ decline has probably been oversimplified. 
Product quality adds to the challenge. NPR reported that independent testing shows considerable variability, with labels not always matching contents.
Research presented at a NAD+ conference earlier this year also suggested that gut bacteria convert most orally supplemented NR or NMN into niacin before it enters the bloodstream.
What this research means for brands
The research doesn't show that NAD precursors don’t work. The Vilnius team stressed that its study did not assess supplement health effects and that long-term clinical trials are still needed.
Some participants taking NAD-raising supplements had unusually high blood NAD — but higher does not necessarily mean healthier.
For brands, the implication is a shift away from generic “restore youthful levels” claims.
Researchers are increasingly focusing on more defined populations, such as older adults with significant muscle loss, people with mitochondrial disease and patients with specific metabolic conditions.
Robust clinical evidence, transparent testing and carefully substantiated claims look set to define the next phase of the category.
