NMN Blood Test: How to Know If It's Working

NMN (nicotinamide mononucleotide) has become one of the most talked-about supplements in the longevity world. Popularised by Harvard geneticist David Sinclair and backed by a growing body of clinical research, NMN works as a direct precursor to NAD+ — a coenzyme essential for cellular energy production, DNA repair, and the regulation of ageing pathways.

The problem? There is no standard NMN blood test. You cannot walk into a GP surgery or order a routine panel that directly measures NAD+ levels in your cells. So how do you know if your NMN supplement is actually doing anything?

The answer lies in tracking the downstream biomarkers that NMN is expected to improve. A comprehensive blood test gives you a measurable, objective picture of how your body is responding — from metabolic health and inflammation to liver function and hormonal balance.

This guide explains exactly which blood markers to monitor, when to test, and what improvements to look for when supplementing with NMN.

Why You Need a Blood Test Before Starting NMN

Starting NMN without a baseline blood test is like beginning a training programme without knowing your current fitness level. You might feel different after a few weeks, but subjective impressions are unreliable. Energy levels fluctuate. Sleep quality changes with the seasons. Placebo effects are real.

A blood test taken before you begin supplementing gives you hard numbers. When you retest three months later, you are comparing like with like. Did your HbA1c drop? Has your cholesterol/HDL ratio improved? Is your inflammation marker trending downward? These are questions only data can answer.

This matters even more for NMN because, as we will see, the clinical evidence shows that NAD+ levels rise reliably with supplementation, but the knock-on effects on standard blood markers can be subtle and take time to appear.

The Biomarkers to Track When Taking NMN

NMN works by replenishing NAD+, which declines naturally with age. NAD+ is involved in hundreds of enzymatic reactions across your body, so the potential downstream effects touch multiple systems. Below are the six categories of biomarkers worth monitoring, along with the specific tests to request.

1. Metabolic Markers: Insulin Sensitivity and Blood Sugar

NAD+ plays a central role in glucose metabolism. One of the most cited NMN studies — published in Science in 2021 — found that 250 mg of NMN daily for 10 weeks significantly improved insulin-stimulated glucose disposal in postmenopausal women with prediabetes. Skeletal muscle insulin signalling increased in the NMN group but not in the placebo group.

A 2024 meta-analysis of eight randomised controlled trials (342 participants) found that subgroup analysis showed NMN's most prominent impact was on HOMA-IR (a measure of insulin resistance), particularly at lower doses. However, the overall meta-analysis found no statistically significant benefit on fasting glucose, fasting insulin, or HbA1c across all studies combined.

What this means for you: If you have insulin resistance or prediabetes, NMN may offer measurable improvements in glucose handling. If you are already metabolically healthy, changes in HbA1c may be too small to detect on a standard blood test — but tracking it still establishes an important baseline.

Markers to test: HbA1c, fasting glucose, fasting insulin

2. Lipid Profile: Cholesterol and Triglycerides

NAD+ influences lipid metabolism through its interaction with sirtuins — the "longevity genes" that Sinclair's lab has studied extensively. In animal models, NMN supplementation has repeatedly shown improvements in lipid profiles. Human data is more nuanced.

A 2022 study in healthy volunteers found that NMN significantly reduced blood triglyceride levels. The 2024 meta-analysis noted that while the overall effect on lipid profiles was not statistically significant across all studies, NMN showed the most consistent benefit in reducing triglycerides and improving lipid markers in overweight individuals.

Markers to test: Total cholesterol, cholesterol/HDL ratio, triglycerides, non-HDL cholesterol

3. Liver Function: ALT and GGT

Your liver is where much of the NAD+ metabolism happens, making liver enzymes some of the most directly relevant markers for NMN users. The 2024 meta-analysis of nine NMN studies (412 participants) found a significant positive effect on ALT levels, with NMN supplementation associated with reduced aminotransferase levels in middle-aged and older adults.

Animal studies have been even more striking. NMN treatment restored ALT and AST levels to youthful ranges in aged mice with liver injury, and NMN has been shown to reduce liver inflammation and fibrosis in disease models.

What this means for you: If your ALT or GGT levels are elevated (common in people with fatty liver, high alcohol intake, or metabolic syndrome), NMN may contribute to measurable improvements. Liver function panels are also important safety markers — if NMN were causing harm, these would be the first to flag it.

Markers to test: ALT, GGT, AST, ALP

4. Inflammation: hsCRP

Chronic low-grade inflammation — sometimes called "inflammaging" — is a hallmark of biological ageing. NAD+ supports anti-inflammatory pathways, and NMN has been shown to reduce interleukin-6 (IL-6) and other inflammatory cytokines in animal models.

In humans, the evidence is still emerging. No large-scale trial has demonstrated a statistically significant reduction in CRP or hsCRP from NMN alone. However, because inflammation is both a driver and a consequence of the metabolic dysfunction NMN targets, tracking hsCRP provides a useful window into your overall inflammatory load.

What this means for you: hsCRP below 1.0 mg/L is considered optimal for cardiovascular risk. If yours is elevated, it is worth tracking alongside NMN supplementation — especially if you are also making dietary and lifestyle changes. As Peter Attia has emphasised, hsCRP is one of the most actionable markers in a longevity-focused blood panel.

Marker to test: hsCRP (high-sensitivity C-reactive protein)

5. Hormones: Testosterone, SHBG, and Vitamin D

NAD+ works with sirtuin proteins in Leydig cells to support testosterone production, establishing a direct link between cellular energy metabolism and male hormonal health. Animal studies — including work with Landrace boars — have shown that NMN supplementation significantly increased serum testosterone levels alongside improvements in reproductive markers.

Human evidence is more limited. A study by Yamauchi and colleagues at the University of Tokyo found that NMN supplementation influenced testosterone levels in ageing men, though the researchers called for larger trials to confirm the finding. SHBG (sex hormone-binding globulin) is worth tracking alongside testosterone because it determines how much testosterone is biologically available.

Vitamin D is included here not because NMN directly affects it, but because it is a critical cofactor in many of the same ageing pathways. Low vitamin D is associated with accelerated biological ageing, and ensuring adequate levels (above 75 nmol/L) supports the metabolic processes NMN is trying to enhance.

Markers to test: Testosterone, SHBG, vitamin D

6. Kidney Function and Biological Age Markers

NAD+ depletion has been linked to age-related kidney decline, and eGFR (estimated glomerular filtration rate) is one of the most reliable markers of biological ageing available in standard blood work. A declining eGFR tracks closely with biological age, and maintaining healthy kidney function is a core goal of any longevity strategy.

A 2022 clinical trial found that blood biological age increased significantly in the placebo group but stayed unchanged in all NMN-treated groups at day 60 — a meaningful finding suggesting NMN may slow at least some measurable aspects of biological ageing.

Markers to test: eGFR, creatinine, urea

Complete NMN Blood Test Panel: All Markers at a Glance

Category	Biomarker	Why It Matters for NMN Users	Expected Direction
Metabolic	HbA1c	3-month average blood sugar; reflects insulin sensitivity	Decrease (lower is better)
Metabolic	Fasting glucose	Immediate blood sugar control	Decrease or stable
Lipids	Cholesterol/HDL ratio	Cardiovascular risk; sirtuin-mediated lipid metabolism	Decrease (lower is better)
Lipids	Triglycerides	Significant reduction shown in human trial	Decrease
Lipids	Non-HDL cholesterol	Better predictor of CV risk than LDL alone	Decrease
Liver	ALT	Significant improvement in 2024 meta-analysis	Decrease (within range)
Liver	GGT	Liver stress and metabolic dysfunction	Decrease (within range)
Inflammation	hsCRP	Chronic low-grade inflammation; inflammaging	Decrease
Hormones	Testosterone	NAD+ supports Leydig cell function	Increase (in men)
Hormones	SHBG	Determines bioavailable testosterone	Stable or decrease
Hormones	Vitamin D	Cofactor in ageing pathways; ensure adequacy	Maintain above 75 nmol/L
Kidney	eGFR	Biological age marker; kidney function	Stable or increase
Kidney	Creatinine	Kidney filtration; paired with eGFR	Stable (within range)

The NMN Testing Schedule: When to Get Blood Work Done

Timing matters. NMN is not a pharmaceutical with an immediate, measurable effect on blood chemistry. NAD+ levels rise within days of starting supplementation — clinical trials have measured significant increases at day 30 — but the downstream effects on metabolic, lipid, and inflammatory markers take longer to materialise.

Timepoint	Purpose	What to Look For
Baseline (before starting NMN)	Establish your personal reference ranges	Record all values. Note any markers already outside optimal range — these are your targets.
3 months	First meaningful comparison point	HbA1c (3-month marker by definition). Early lipid and liver enzyme changes. Triglyceride reduction may already be visible.
6 months	Full assessment of NMN impact	Compare all markers to baseline. Evaluate trends rather than isolated values. Hormonal changes may take this long to appear.
12 months (annual)	Long-term monitoring	Confirm sustained improvements. Assess biological age trajectory. Adjust dose or protocol as needed.

Testing tips: Always test fasting (at least 8–12 hours). Test at the same time of day each round — morning is ideal, as testosterone and cortisol follow circadian rhythms. Avoid intense exercise for 48 hours before your blood draw, as this temporarily elevates liver enzymes and inflammatory markers.

What the Clinical Evidence Actually Shows

Honesty matters here. NMN is one of the most researched NAD+ precursors, but the human evidence base is still young. Here is a fair summary of where things stand in 2025:

What is well-established

• NMN reliably raises NAD+ levels. Multiple randomised controlled trials confirm that oral NMN at 250–900 mg/day increases blood NAD+ and its metabolites by approximately 130–150%. This effect is consistent and dose-dependent.
• NMN is safe. Across all completed human trials, NMN has not triggered any adverse physiological effects. Liver and kidney safety markers remain stable or improve.
• NAD+ declines with age. This is one of the most replicated findings in ageing research. By age 50, NAD+ levels may be half what they were at 20.

What is promising but needs more data

• Insulin sensitivity improvements in prediabetic women (250 mg/day for 10 weeks, published in Science).
• Triglyceride reduction in healthy individuals.
• ALT improvements across a meta-analysis of nine studies (412 participants).
• Biological age stabilisation — one trial showed biological age increased in the placebo group but remained unchanged in NMN-treated groups.
• Physical function improvements — gait speed and walking test performance improved in older adults.
• Sleep quality improvements at 12 weeks.

What remains unproven in humans

• Direct effects on HbA1c in metabolically healthy individuals.
• Significant cholesterol or LDL changes from NMN alone.
• Testosterone increases (animal data is positive; human data is preliminary).
• CRP or hsCRP reduction from NMN supplementation.
• Lifespan extension (no human longevity trials exist).

NMN Dosing: What Clinical Trials Use

Human trials have tested NMN at doses ranging from 250 mg to 1,000 mg per day, with some studies going up to 2,000 mg. The most commonly studied dose is 250 mg/day, which is where the insulin sensitivity data comes from. Higher doses (600–900 mg) produced greater NAD+ increases in a dose-dependent manner.

David Sinclair has publicly stated he takes 1,000 mg (1 g) of NMN daily as part of his longevity protocol, alongside resveratrol, fisetin, taurine, and low-dose rapamycin. However, his personal regimen should not be confused with clinical evidence — it reflects his interpretation of the research applied to his own health.

Most longevity practitioners recommend starting at 250–500 mg/day and assessing response via blood work before increasing. There is no evidence that doses above 1,000 mg provide additional benefit.

How to Interpret Your Results: What "Working" Actually Looks Like

When you compare your 3-month or 6-month blood test to your baseline, keep these principles in mind:

Look for trends, not miracles. NMN is not a statin. You are unlikely to see a 30% drop in LDL cholesterol. What you might see is a steady, modest improvement across multiple markers simultaneously — a slightly lower HbA1c, a triglyceride drop of 10–15%, ALT moving from the upper end of normal to the middle. These small shifts across many markers are exactly what a systemic intervention like NAD+ replenishment would be expected to produce.

Context matters enormously. If your baseline markers were already optimal, NMN may maintain them rather than improve them — and that is still a meaningful result. The clinical trial that showed biological age stabilisation in the NMN group while it increased in the placebo group illustrates this perfectly. Sometimes the benefit is not getting worse.

Isolate your variables. If you start NMN at the same time as a new exercise programme, a dietary overhaul, and three other supplements, you cannot attribute any blood test changes to NMN specifically. Ideally, establish your baseline, start NMN alone, and retest before adding other interventions. If that is not practical, at least document everything so you can make informed assessments.

Red flags to watch for. NMN has an excellent safety profile across all clinical trials. However, any supplement deserves monitoring. If you see unexplained increases in liver enzymes (ALT, GGT) or kidney markers (creatinine, reduced eGFR), discuss the results with your GP. These changes are unlikely to be caused by NMN at standard doses, but blood work protects you either way.

NMN and Blood Tests: The Bottom Line

NMN is one of the more evidence-backed supplements in the longevity space, but "evidence-backed" does not mean "proven to work for every biomarker." The research clearly shows that NMN raises NAD+ levels, and there are encouraging signals across insulin sensitivity, triglycerides, liver enzymes, physical function, and biological age markers. The gaps — particularly around cholesterol, testosterone, and inflammation — are gaps in research, not evidence of absence.

What separates informed NMN users from hopeful ones is data. A blood test before you start. A blood test at three months. A blood test at six months. The numbers either move in the right direction or they do not. That is how you know if NMN is working — for you, specifically, not in a population average from a clinical trial.

If you are serious about longevity, treat your blood work the way Peter Attia treats his patients' lab results — as the single most important source of truth about what is happening inside your body.