CD38: The Enzyme Quietly Destroying Your NAD+ as You Age

Longevity Science · Updated June 2026

You have probably read that NAD+ declines by roughly 50% between your 20s and 60s. Most explanations stop there. What they do not explain is the primary biological mechanism driving that decline — and it is not just ageing. It is a specific enzyme called CD38.

CD38 is the longevity science concept that Tru Niagen has covered and nobody else in the Australian supplement market has explained clearly. It is also the mechanistic reason why NMN supplementation becomes more relevant with age — not less — and why the senolytic Quercetin in a complete NMN formula addresses two problems simultaneously: senescent cell clearance AND CD38 inhibition.

What CD38 Is and What It Does

CD38 is a glycoprotein enzyme expressed primarily on the surface of immune cells — B cells, T cells, and natural killer cells — as well as in muscle, liver, and brain tissue. It has two primary functions: it acts as a signalling receptor, and it functions as an NAD+-consuming enzyme (an NADase and ADP-ribose cyclase).

As an NADase, CD38 breaks down NAD+ into nicotinamide and other metabolites as part of cellular signalling. This is a normal biological function — CD38 plays roles in immune activation, calcium signalling, and insulin secretion. The problem is not that CD38 exists. The problem is that CD38 activity increases dramatically with age and inflammation.

Why CD38 Increases with Age

Two connected processes drive CD38 accumulation with age:

1. Inflammageing — chronic low-grade inflammation: As you age, inflammatory signalling increases — a process called inflammageing. CD38 is expressed on immune cells, and immune activation increases CD38 expression. More inflammation = more immune activation = more CD38 = more NAD+ consumed.

2. Senescent cell accumulation: Senescent cells secrete inflammatory signals (the SASP) that activate immune cells, which upregulate CD38. As senescent cells accumulate with age, they drive more CD38 expression via this inflammatory cascade. This is the mechanism that connects cellular senescence to NAD+ depletion — not just through age, but through a biological feedback loop.

The result: by your 50s and 60s, you have more CD38 activity consuming your NAD+ than you did at 30, and you are simultaneously producing less NAD+ through natural synthesis. The combination produces the 50% NAD+ decline documented in research — and it explains why that decline tracks so closely with biological ageing markers.

The Landmark Research on CD38 and NAD+ Decline

The definitive study was published in 2016 by Camacho-Pereira et al. in Cell Metabolism. The key findings:

• CD38 activity increases significantly in liver, muscle, and white adipose tissue with age in mice
• CD38 knockout mice — genetically engineered to lack CD38 — showed significantly higher NAD+ levels at equivalent ages
• CD38 knockout mice were largely protected from the age-related NAD+ decline observed in normal mice
• Senescent cells activate macrophages which express high levels of CD38 — confirming the senescence-inflammation-CD38-NAD+ axis

This research established CD38 as a primary driver of age-related NAD+ depletion — not just a bystander. The implication: addressing NAD+ depletion comprehensively requires both restoring what is lost (NMN) and reducing what is being consumed (CD38 inhibition).

The Quercetin-CD38 Connection: A Dual-Action Ingredient

This is where the formula logic of Nadovia's Longevity Complex becomes particularly compelling. Quercetin — included at 300mg per serving — is a known CD38 inhibitor.

Research by Escande et al. (2013, Chemistry & Biology) identified Quercetin as one of the most potent natural CD38 inhibitors, with an IC50 (the concentration needed to inhibit 50% of CD38 activity) of approximately 16μM. In practical terms: Quercetin supplementation can reduce CD38 activity, thereby slowing the enzyme-driven NAD+ depletion that compounds age-related decline.

So Quercetin in a longevity formula does two distinct things:

1. As a senolytic: Clears senescent cells that would otherwise continue driving inflammation and CD38 expression (see our Quercetin senolytic guide)
2. As a CD38 inhibitor: Directly reduces the enzyme activity consuming your NAD+ reserves

These are complementary but distinct mechanisms. Quercetin is not simply an antioxidant add-on in a longevity formula — it is a mechanistically justified component that addresses NAD+ depletion from a different angle than NMN does.

Why NMN Matters More as CD38 Activity Increases

Here is the counterintuitive implication of CD38 science: NMN supplementation becomes more important, not less, as you age — because CD38 is consuming more NAD+ in an older system.

A 30-year-old with low CD38 activity can maintain reasonable NAD+ levels through natural synthesis. A 55-year-old with elevated CD38 activity, higher inflammation, and accumulating senescent cells is experiencing a multi-directional NAD+ drain that natural synthesis cannot compensate for.

NMN replenishes NAD+ via the salvage pathway — directly providing the precursor to NAD+ conversion. Combined with Quercetin's CD38 inhibition, the effect is two-sided: restore what is lost + reduce what is being consumed. This is the mechanistic rationale for the Nadovia Longevity Complex — not marketing, but biology.

FAQ

References: Camacho-Pereira J et al., Cell Metabolism (2016) — CD38 and NAD+ decline; Escande C et al., Chemistry & Biology (2013) — Quercetin as CD38 inhibitor; Chini CCS et al., Cell Metabolism (2020) — CD38 and inflammageing; pubmed.ncbi.nlm.nih.gov. Not medical advice.