Nicotinamide adenine dinucleotide metabolism and arterial stiffness after long-term nicotinamide mononucleotide supplementation: a randomized, double-blind, placebo-controlled trial

Arteries become stiffer with age, and stiffer arteries are a well-established risk factor for cardiovascular events. One way to measure arterial stiffness in a clinic is brachial-ankle pulse wave velocity, or baPWV — essentially how fast a pressure wave travels between the arm and the ankle. Faster waves mean stiffer arteries. This trial asked whether taking NMN for three months could reduce baPWV in middle-aged adults.

Thirty-six healthy Japanese participants aged 40 to 59 were randomly assigned to take either 250 mg of NMN per day (as two 125 mg capsules) or a matching placebo for 12 weeks. Neither participants nor investigators knew who was receiving what. The researchers measured serum levels of NAD+ and its metabolites, blood pressure, ABI, baPWV, blood chemistry, and several other markers before and after the intervention.

The intervention was well tolerated across the 12 weeks with no adverse events reported at 250 mg/day. Serum nicotinamide — one of the downstream products of NAD+-consuming enzymes — rose significantly in the NMN group relative to placebo, indicating that NMN did engage NAD+ metabolism. Average baPWV in the NMN group trended downward by roughly 25 cm/s over the trial while the placebo group did not change, but the difference between the groups did not reach statistical significance in the overall population.

When the authors looked at pre-specified subgroups with cardiovascular risk factors, participants with above-average BMI or above-average blood glucose in the NMN group showed a statistically significant reduction in baPWV compared to the placebo subgroup with the same characteristics. This subgroup pattern is consistent with the possibility that NMN's vascular effect is easier to detect in people whose arteries are already under more metabolic stress, but subgroup findings from a small trial are hypothesis-generating rather than confirmatory.

• Serum nicotinamide rose significantly in the NMN group over 12 weeks (from 10.4 to 16.5 ng/mL, a 57.6% increase) while falling in the placebo group (14.9 to 10.9 ng/mL, a 26.8% decrease). Serum NAD+ and NMN themselves were detectable but below the assay's lower limit of quantification in both groups.
• Average baPWV in the NMN group decreased by approximately 25 cm/s over 12 weeks; placebo group values were essentially unchanged. The between-group difference did not reach statistical significance (p=0.097 for average baPWV).
• In the pre-specified subgroup of participants with above-average BMI (n=7 placebo, n=8 NMN), NMN significantly reduced baPWV relative to placebo (p=0.007).
• In the subgroup with above-average blood glucose (n=11 placebo, n=7 NMN), NMN significantly reduced baPWV relative to placebo (p=0.019).
• 250 mg/day NMN over 12 weeks was well tolerated. There were no significant changes in body weight, BMI, blood pressure, liver enzymes, lipid panel, hematology, or hormones in the NMN group relative to placebo, and no adverse events were reported.
• SIRT1 mRNA expression in whole blood, urinary 8-hydroxydeoxyguanosine, and skin advanced glycation end-products did not differ significantly between groups.

• Sample size was small (n=34 completers, roughly 17 per arm), limiting statistical power for the primary between-group comparison of baPWV.
• The primary between-group difference in baPWV in the overall population did not reach statistical significance. The subgroup findings in participants with above-average BMI or blood glucose are hypothesis-generating and would need to be replicated in a trial powered for those specific groups.
• Baseline baPWV values differed between the two groups (particularly on the left side), which the authors flagged as a possible source of bias despite randomization. The between-group analysis was adjusted for baseline as a covariate.
• NAD+ and NMN were measured in serum rather than in whole blood or peripheral blood mononuclear cells. Serum is not the compartment where these molecules are most abundant, so the assay could not quantify them at typical intracellular concentrations. The authors acknowledge this limits interpretation of NAD+ pharmacodynamics.
• Participants continued taking pre-existing supplements during the trial, and consumption of some supplements (vitamin C, vitamin B complex, omega-3) differed between groups. Omega-3 in particular has known vascular effects and was more common in the placebo group.
• All seven authors are employees of DHC Corporation, which funded the study and manufactures NMN. The trial was pre-registered with a Japanese clinical trial registry (UMIN000045205).
• The study population was healthy middle-aged Japanese adults. Findings may not generalize to other age ranges, other ancestry groups, or individuals with established cardiovascular disease.