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NAD+ is not a trendy supplement ingredient. It is the most important coenzyme in your body for energy production, DNA repair, and cellular signalling. Every cell in your body requires it. And by the time you hit 50, your levels have dropped by roughly half compared to where they were in your twenties.
This is not theoretical. It is measurable in blood and muscle tissue. The interventions designed to raise NAD+ levels are now being tested in human clinical trials, and the early data is genuinely interesting.
The question for men in their 30s, 40s, and 50s is straightforward: does supplementing with NAD+ precursors actually do anything useful, and if so, which precursor should you take?
What NAD+ actually does
Nicotinamide adenine dinucleotide (NAD+) is a coenzyme involved in over 500 enzymatic reactions in the body. The three most relevant to ageing and performance are:
Sirtuin activation. Sirtuins are a family of seven proteins (SIRT1 through SIRT7) that regulate cellular health, inflammation, and metabolism. They are sometimes called "longevity genes" though that oversimplifies their role. What is accurate is that sirtuins require NAD+ to function. When NAD+ drops, sirtuin activity drops.
PARP-mediated DNA repair. Poly(ADP-ribose) polymerases are enzymes that repair damaged DNA. They consume NAD+ as fuel. As you age, DNA damage accumulates and PARPs consume more NAD+, creating a vicious cycle where the repair machinery depletes its own fuel supply.
Mitochondrial biogenesis. NAD+ is central to the electron transport chain, the process by which mitochondria produce ATP (cellular energy). Lower NAD+ means less efficient energy production. This is partly why fatigue and reduced exercise capacity are hallmarks of ageing.
The decline is not subtle:
The human evidence
The most important human trial to date for NMN supplementation is the Yoshino et al. (2021) study published in Science:
This study is significant for two reasons. First, it demonstrated that oral NMN supplementation actually raises NAD+ levels in muscle tissue. This was previously assumed from animal data but not confirmed in humans. Second, the improvement in insulin sensitivity has broad metabolic implications that extend beyond the specific population studied.
For NR (nicotinamide riboside), the Martens et al. (2018) trial showed that 1,000mg daily for 6 weeks reduced systolic blood pressure and aortic stiffness in healthy middle-aged and older adults. The Elhassan et al. (2019) study confirmed that NR supplementation elevates NAD+ metabolites in skeletal muscle of older men.
NMN vs NR: the actual differences
This is where the marketing gets loud and the science gets nuanced. Both NMN and NR are NAD+ precursors. Both raise NAD+ levels. The debate is about which does it more effectively.
Molecular pathway. NMN is one step closer to NAD+ in the biosynthesis pathway. NR must first be converted to NMN (by the enzyme NRK), which is then converted to NAD+ (by the enzyme NMNAT). NMN skips the NRK step. In theory, this makes NMN more efficient. In practice, the body is remarkably good at handling both conversions.
Bioavailability. NMN has a higher molecular weight than NR, which raised early questions about whether it could cross the gut barrier intact. The discovery of the Slc12a8 transporter in 2019 (a dedicated NMN transporter in the small intestine) largely resolved this concern. Both compounds are orally bioavailable.
Price per effective dose. NR was historically cheaper because Chromadex (the company behind Tru Niagen) held key patents and had economies of scale. NMN prices have dropped significantly as more manufacturers have entered the market. At current UK prices, the cost per milligram is comparable.
Evidence base. NR has a slightly larger body of published human trials because it has been commercially available longer. NMN is catching up rapidly. Neither has a decisive advantage in the evidence.
The honest assessment. If you forced me to choose, I would lean slightly toward NMN based on the more direct conversion pathway and the Yoshino 2021 data. But the difference is marginal. Consistency of supplementation matters more than which precursor you pick.
What actually matters in an NAD+ supplement
The form of the supplement matters less than the quality and dose:
- Purity. Look for products that publish third-party purity testing results. NMN and NR can degrade if stored improperly, and some products have tested below their labelled potency.
- Dose. The Yoshino trial used 250mg daily. Most longevity researchers who take NMN themselves use 500mg to 1,000mg daily. Under 250mg is likely subtherapeutic based on current data.
- Enteric coating vs standard capsule. Some NMN products use enteric coating to survive stomach acid. The evidence for whether this significantly improves bioavailability is mixed. The Slc12a8 transporter is in the small intestine, so surviving the stomach intact is theoretically beneficial.
- Sublingual vs oral. Sublingual delivery bypasses first-pass metabolism. Some products offer this route. The data on whether sublingual NMN achieves meaningfully higher blood levels is preliminary.
- Storage. NMN is hygroscopic (absorbs moisture) and can degrade at room temperature. Store it in a cool, dry place. Some products require refrigeration.
I have been taking 500mg of NMN daily for about eight months. What I notice: slightly better sustained energy through the afternoon, and my fasted morning heart rate variability has improved. What I do not notice: any dramatic change in how I feel day-to-day. This is consistent with what most researchers say. NAD+ supplementation is playing a long game. You are not going to feel 25 again after a week. The question is whether maintaining NAD+ levels slows the rate at which things deteriorate, and that is a question we probably will not have a definitive answer to for another decade. I take it because the risk-benefit ratio is favourable and the mechanistic evidence is strong.
Lifestyle factors that deplete NAD+
Supplementation is one side of the equation. The other side is understanding what accelerates NAD+ decline:
Alcohol. Ethanol metabolism consumes NAD+ directly. The enzyme alcohol dehydrogenase uses NAD+ to convert alcohol to acetaldehyde. Heavy drinking creates a significant drain on cellular NAD+ reserves. This is one of the mechanisms by which chronic alcohol use accelerates biological ageing.
UV damage. Sun exposure causes DNA damage, which activates PARP enzymes, which consume NAD+. Cumulative sun damage is a significant contributor to NAD+ decline, particularly in the skin.
Chronic inflammation. Inflammatory signalling (NF-kB pathway) increases the activity of CD38, an enzyme that degrades NAD+. Chronic low-grade inflammation from poor diet, poor sleep, or gut dysbiosis accelerates NAD+ loss.
Poor sleep. NAD+ levels follow a circadian rhythm. Disrupted sleep disrupts this rhythm and appears to reduce NAD+ regeneration during rest periods.
Protocol
Dosing. 250mg to 1,000mg daily. Start at 250mg for the first two weeks and increase if well-tolerated. Most people settle at 500mg.
Timing. Morning, with or without food. NAD+ levels naturally peak in the morning and taking NMN early in the day aligns with this circadian rhythm. Some people report difficulty sleeping if they take NMN in the evening, possibly due to its energising effects.
Cycling. This is debated. Some researchers (including David Sinclair) take NMN daily without cycling. Others suggest 5 days on, 2 days off. There is no published human data comparing cycling protocols, so this remains a matter of personal preference.
Combination with other supplements. NMN is often stacked with resveratrol (a sirtuin activator), TMG (trimethylglycine, to support methylation), and vitamin D. The rationale is that raising NAD+ activates sirtuins, and resveratrol may further enhance sirtuin activity. This is theoretically sound but not yet validated in human combination trials.
Frequently asked questions
How long to see results?
Most people who report subjective improvements notice them at 4 to 8 weeks. The cellular changes (NAD+ elevation, improved mitochondrial function) begin within days but take weeks to translate into anything you would notice. Blood NAD+ levels can be tested via specialist labs if you want objective measurement.
Can I take NMN and NR together?
You can, but there is no evidence this is more effective than taking either one alone. They both feed into the same pathway. Taking both may simply be redundant. Choose one and take it consistently.
Does it interfere with medication?
No significant drug interactions have been reported in published trials. However, if you are on immunosuppressant medication, diabetes medication, or blood thinners, consult your doctor. NMN's effect on insulin sensitivity could theoretically interact with diabetes medication dosing.
Is it worth it for men in their 30s?
NAD+ decline begins in the late twenties, but it is modest at that stage. The strongest case for supplementation is in men over 40, where the decline is more pronounced and the metabolic consequences are more apparent. That said, if you have the budget and want to be proactive, starting earlier is not harmful. The question is whether the benefit justifies the cost at a younger age.
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