The Longevity Test That Might Be Telling You Nothing

A study recently published in Nature Metabolism calls into question one of the most popular biomarkers in the longevity space. What this means for practice — and why precise diagnostics are more than the next trend test.

The narrative has been running the same way for years. Your NAD+ declines with age, your cells run dry, and the solution is either a supplement or a blood test that tracks the whole thing. Manufacturers sell both, influencers recommend it, clinics offer panels. A study published in Nature Metabolism in 2026 has just made that story considerably more complicated.

What the Researchers Did

The scientists measured whole-blood NAD+ across seven independent cohorts. Cross-sectional comparisons of younger versus older adults, multi-week exercise programs, dietary interventions, combined lifestyle programs. The methodology was deliberately rigorous: UHPLC with high-resolution mass spectrometry, validated for real-world analytical variation, with clearly documented statistical power.

What They Found

In every single cohort, blood NAD+ levels remained stable. No meaningful decline with age. No measurable response to exercise, diet, or multimodal lifestyle interventions.

The only thing that shifted the value was NR supplementation (nicotinamide riboside). And the researchers had included that deliberately, to demonstrate that their measurement method was sensitive enough to detect an effect at all.

Why This Is Relevant to Your Practice

A good portion of the popular NAD+ narrative rests on animal studies and reviews, not on clean human data. Where NAD+ in humans actually comes under pressure are clearly defined conditions: heart failure, certain neurological diseases, severe alcohol dependence. That is a different claim from "ageing depletes your NAD+ pool, so you need to replenish it."

The study is not a blanket verdict against NAD+ biology. NR has well-documented anti-inflammatory effects, and for specific indications such as peripheral arterial disease the evidence is growing. What the study dismantles is the assumption that blood NAD+ is a universal biomarker for healthy ageing and that it can be used to meaningfully track biological age.

Why Precise Diagnostics Are More Than Trend Tests

This is precisely where it becomes clear why we need to approach health both holistically and precisely.

Precise means: A test is only useful if it measures what it claims to measure. NAD+ in blood is not NAD+ in muscle, not in the brain, not in adipose tissue. If the question is longevity, the answer is not "one more trend measurement" but a carefully curated set of validated markers.

Holistic means: No single value tells the whole story. A "biological age" derived from a single marker is a stage trick, not a clinical tool. Anyone who takes longevity seriously works in combination: lab plus genetics plus lifestyle plus trajectory over time.

What This Means for Evidence-Based Practice

Instead of chasing the next hype marker, we focus on what actually works:

  • Inflammation: CRP, IL-6, TNF-α — with demonstrated relationships to cardiovascular endpoints
  • Metabolic health: glucose-insulin homeostasis, HbA1c, HOMA-IR
  • Iron metabolism: ferritin as a marker of oxidative stress and inflammation
  • Cardiorespiratory fitness: VO2max, resting HRV
  • Sleep quality: objective parameters, not subjective assessments

Every single marker with a demonstrated relationship to hard endpoints. Not because it is new, but because it works.

From Data to Outcomes

At SLOW we select markers by evidence, not by hype. Our 700+ biomarkers are scientifically validated and evaluated within an integrated ecosystem. Not as isolated individual values, but as part of a complete picture.

This means: less time interpreting fragmented individual tests. More time supporting your clients. Measurable outcomes instead of marketing promises.

Real change comes from real data.

Which markers do you use in practice for serious longevity consulting, and which have you deliberately removed from your panel?

Source: Janssens GE et al. Human whole-blood NAD+ levels do not vary with age or lifestyle interventions. Nature Metabolism (2026). Available open access.