Blood NAD+ Doesn't Decline With Age, the Best Measurement Yet Finds

What seven cohorts actually found

The Houtkooper lab published the work as a Brief Communication in Nature Metabolism. Using a rigorously validated ultra high performance liquid chromatography method coupled with high resolution mass spectrometry, the team quantified NAD+ across seven separate human cohorts. Whole blood NAD+ levels came back remarkably stable with age and stable across lifestyle interventions like diet and exercise. The one thing that did move the number was nicotinamide riboside supplementation, which raised blood NAD+ as expected. Two things are true at once here. The pills do what they claim, they raise the number in blood. And that number apparently was not falling on its own in the first place, at least not in a way this method could detect.

The methodological point is a big part of why this lands. Prior studies reporting an age related decline in blood NAD+ have been inconsistent with each other, and the authors argue that analytical variability, not biology, plausibly explains a good share of that inconsistency. In other words, some of what looked like a real decline in earlier, less controlled measurements may simply have been noise.

The paper is not going unanswered. It has already picked up citations and a real amount of attention since it published, and at least one supplement brand, Tru Niagen, has posted its own rebuttal. Reading that rebuttal is useful precisely because of what it argues. It leans on the blood versus tissue distinction, the same limit this paper states about itself rather than something the rebuttal discovered. That is not nothing, tissue NAD+ genuinely might tell a different story, but it is a reason to stay curious rather than a reason to dismiss what seven cohorts of blood measurement actually found.

The gap between the pill and the premise

This matters because the entire NAD+ supplement category, plus a growing at home blood testing business built around it, rests on the premise that your NAD+ is declining and needs restoring. The authors are careful about what they are and are not claiming, and so should anyone writing about it. The paper does not say NAD+ never declines anywhere in the body. It says whole blood NAD+, specifically, did not decline across seven cohorts studied with their method. That distinction is exactly why the timing here is interesting. A liposomal NAD+ product launched into this category just two days before this paper resurfaced in the research world, pitching better delivery of a molecule whose blood level deficit this study could not confirm. Both the delivery claim and the decline claim are, at minimum, unproven on their own terms, and only one of them usually gets examined.