Oral administration of a moderate dose of NMN (250 mg/day) can safely promote NAD+ metabolism and improve vascular function in humans
with most significant effects observed in participants with a higher body mass index (BMI) or higher blood glucose levels
This blog reviews a recent study that highlights the effects of NMN for its consumers between the age of 40 and 59.
While we have known for years that NMN reverses various signs of vascular aging in rodents, this trial provides a highly structured look at what actually happens in human biology over a long period.
Here is a deeper, broken-down look at the study’s biochemistry, methodology, and nuances.
1. The Biochemical Problem: The “NAMPT” Bottleneck
To understand why the researchers gave participants NMN, you have to look at how our bodies make NAD+ (the coenzyme responsible for cell energy and DNA repair).
Our cells primarily rely on a recycling loop called the Salvage Pathway. Usually, the body takes Vitamin B3 (Nicotinamide) and uses a master enzyme called NAMPT to convert it into NMN, which then becomes NAD+.
The Aging Problem: As we get older, NAMPT enzyme levels drop drastically. This creates a bottleneck—even if you have enough Vitamin B3, your body can't convert it fast enough, causing NAD+ levels to plummet.
By giving participants oral NMN, the researchers bypassed this broken bottleneck entirely. NMN is downstream of the slow enzyme, meaning the body can immediately take it and convert it directly into NAD+.
2. Deep Dive into the Study's Methodology
The researchers used a highly rigorous setup to ensure the data wasn't influenced by outside factors or placebo effects:
The Cohort: 36 healthy men and women between 40 and 59 years old. This age bracket was chosen explicitly because it represents the exact window where natural NAD+ levels begin their steep age-related decline.
The Routine: It was a randomized, double-blind, placebo-controlled trial. Half took a placebo; the other half took a 250 mg daily dose of NMN (divided into two 125 mg capsules per day) for 12 weeks.
The Metrics: The team didn't just track how the participants "felt." They performed comprehensive blood panels, monitored metabolic markers, measured exact NAD+ metabolite levels in the serum, and evaluated arterial health.
3. Understanding the Results: What Exactly Happened?
Blood Chemistry & The "Proof of Absorption"
A common critique of oral supplements is that the stomach destroys them before they can do anything. The researchers proved that NMN survives digestion. When they analyzed the blood serum of the NMN group, they found significantly elevated levels of nicotinamide and other key NAD+ metabolites. This proved that the oral NMN was successfully absorbed by the gut, entered the bloodstream, and effectively turned on the body's NAD+ manufacturing machinery.
The Vascular Impact: Pulse Wave Velocity (PWV)
To measure arterial stiffness, the researchers utilized a test called baPWV (brachial-ankle Pulse Wave Velocity). This measures the speed at which a blood pressure wave travels down your arteries.
Stiff, aged arteries are rigid, meaning the pressure wave travels incredibly fast.
Flexible, youthful arteries absorb the shock of the heartbeat, meaning the wave travels slower.
Healthy, Flexible Artery ---> Wave travels slower (Lower PWV)
Stiff, Aged Artery ---> Wave travels faster (Higher PWV)
The Catch in the Data: When looking at the entire NMN group as a whole, the pulse wave velocity values decreased (a sign of more flexible arteries), but the change trended just shy of being "statistically significant" compared to the placebo group.
The Sub-Group Breakthrough: However, when the scientists dug deeper and isolated participants who had higher baseline body mass index (BMI) or elevated blood glucose levels, the results changed completely. For these individuals, the reduction in arterial stiffness was statistically significant. This implies that NMN’s vascular benefits are most pronounced in individuals who are already experiencing early metabolic stress or cardiovascular stiffening.
4. Safety & Side Effects
A major goal of a 12-week human study is establishing safety. The trial reported:
Zero adverse events: No flushing, gastrointestinal distress, or organ toxicity was observed.
Stable blood markers: Liver enzymes, kidney function markers, and metabolic profiles remained completely safe and normal throughout the 90 days.
Summary & Takeaway
This study proved that a relatively modest dose of NMN (250 mg/day) safely boosts human NAD+ metabolism. While it didn't magically rejuvenate the arteries of perfectly healthy middle-aged adults overnight, it demonstrated a clear protective benefit for those carrying extra weight or metabolic strain, opening the door for NMN as a targeted therapeutic tool for cardiovascular health.
Reference
Katayoshi, T., Uehata, S., Nakashima, N. et al. Nicotinamide adenine dinucleotide metabolism and arterial stiffness after long-term nicotinamide mononucleotide supplementation: a randomized, double-blind, placebo-controlled trial. Sci Rep 13, 2786 (2023). https://doi.org/10.1038/s41598-023-29787-3
