A Blood NAD+ Test Can’t Tell One's Biological Age

Wellness influencers, biohackers, and celebrities all over the globe swear by antiaging supplements to boost the levels of nicotinamide adenine dinucleotide (NAD). A few studies have indicated that levels of the metabolic coenzyme drop during aging, suggesting that supplementing it could help preserve health.¹ However, data from humans remain limited.

Georges Janssens and Riekelt Houtkooper, biochemists at Amsterdam University Medical Center, have previously shown that levels of the oxidized form of NAD (NAD⁺) decline in muscles as people age.² But muscle biopsies to measure NAD⁺ concentrations would be invasive. As a minimally-invasive approach, “We had this idea of taking blood samples and measuring NAD⁺ levels in blood and using that as a marker of biological age,” said Houtkooper.

Recently, Houtkooper, Janssens, and their colleagues analyzed nearly 300 blood samples and found that blood NAD⁺ levels do not fluctuate with age or lifestyle factors such as exercise and diet.³ Their findings, published in Nature Metabolism, reveal that blood-based NAD⁺ levels are not a useful biomarker of aging or lifestyle interventions.

“[The study] is really well done,” said Melanie McReynolds, an NAD⁺ biochemist at Pennsylvania State University, who was not involved with the study. People want an easy biomarker for the body’s NAD⁺ levels, but “the paper and how robustly they did it was needed for the public. The biggest takeaway…[is] whole blood NAD⁺ measurements are really not going to be the way to tell you what's happening,” she said.

Blood NAD⁺ Levels are Remarkably Consistent Through the Ages

To test whether blood could be a marker for NAD⁺ levels, Houtkooper, Janssens, and their colleagues obtained blood samples from people younger than 30 years of age, or older than 60. “The idea was first to have this quick and easy, preferably minimally invasive way of measuring whole blood NAD⁺,” said Maria Trętowicz, a study coauthor and graduate student at Amsterdam University Medical Center.

So, they decided to validate and use a combination of liquid chromatography and mass spectrometry that could measure the level of NAD⁺ in one drop of blood. While they collected blood intravenously for this study, Trętowicz noted that the small volume required means they could also collect it using finger pricks for future studies.

The researchers did not find any significant variation in blood NAD⁺ levels across the different ages, “to our surprise and actually annoyance,” said Houtkooper. “In a way, one could say that it's not the most exciting outcome,” said Trętowicz.

To dig deeper, the researchers started gathering data from different cohorts. To test whether physiological extremes influenced NAD⁺ levels, they analyzed samples from elite athletes and young non-athlete controls. Blood NAD⁺ levels did not differ between the groups. When they got these results, “I would walk around saying my NAD⁺ values are as high as Olympic athletes,” recalled Janssens.

Next, they examined the effect of lifestyle and nutritional interventions. Comparing the NAD⁺ levels in older, frail adults before and after exercise and on a protein-rich diet regimen revealed no changes, validating that NAD⁺ concentrations are stable despite age- and lifestyle-associated factors.

This did not surprise McReynolds. “I never agreed that measuring circulating NAD⁺ was the best path forward,” she said. “The real signal [for NAD⁺ levels] is going to lie deeper”

Are NAD⁺ Supplements Futile?

To understand what their results meant in terms of NAD⁺ supplementation strategies, the researchers measured blood NAD⁺ levels in individuals before and after they took supplements containing nicotinamide riboside, a precursor of NAD⁺. Consistent with previous reports, this treatment increased blood NAD⁺ levels.^4,5

“That was really promising, and it supports that the supplements are in fact doing something,” said McReynolds. She noted that blood NAD⁺ levels could be a readout to assess the uptake and metabolism of supplements such as nicotinamide riboside.

Houtkooper agreed. “It does not mean that NAD-based supplements are worthless,” he said. “Actually, there is some truth to the idea of using NAD⁺ as a target for anti-aging therapy. What we are trying to advocate is that really the field needs rigorous clinical studies.” These kinds of studies could help scientists understand what happens to NAD⁺ levels in different tissues as people age and whether supplements indeed have a beneficial effect.

McReynolds added that while muscle biopsies, although invasive, could offer insight into NAD⁺ dynamics in aging muscle, those insights might not be relevant to other organs. “We really need to identify [if] there could be a circulating biomarker in whole blood that is not NAD⁺ but that could relay what is happening to NAD⁺ in other tissues,” she said.

The researchers have already started investigating this, said Janssens. He reiterated that their findings only indicate that blood is a poor marker of tissue NAD⁺ levels. “Probably the only real implication [of the findings] is indeed that you can't restore your NAD⁺ levels to youthful [ones] in blood because they aren't really changing,” said Janssens. “That doesn't throw out the NAD field, of course.”