Nicotinamide adenine dinucleotide (NAD(H)) and its phosphorylated form NADP(H) are vitamin B 3-derived redox cofactors that have a central role in hundreds of metabolic reactions and post-translational modifications of proteins. Given its essentiality, disturbances in NAD+ homeostasis, and hence, a decline in NAD+ levels, have been associated with multiple health conditions. Several strategies have been deployed to replenish NAD+ levels through feeding with precursors from its three canonical biosynthetic routes: the salvage pathway from nicotinamide (Nam), the Preiss–Handler pathway from nicotinic acid (NA) and the de novo biosynthesis from the essential amino acid tryptophan, which converges on the Preiss–Handler pathway.
a, Schematic of the dynamics of the NAD+ biosynthesis pathways. b–h, Concentrations of NAD+ (red), degradation products (yellow), NAD+ precursors (blue) and NAAD (green) in whole blood at baseline and after 14 days of daily administration of either placebo, Nam, NR or NMN. Data are shown for NAD+ (b), MeNam (c), MeXPY (d), NR (e), NMN (f), Nam (g) and NAAD (h). Significant differential changes over 14 days compared to placebo are indicated (based on two-sided ANCOVA). i–o, Acute effect of the three NAD+ precursors on the NAD+ metabolome at visit 3 (day 1) and visit 4 (day 14). The iAUC over 4 h is shown. Data are shown for NAD+ (i), MeNam (j), MeXPY (k), NR (l), NMN (m), NAM (n) and NAAD (o). Significant differences compared to placebo are indicated for each visit (based on a two-sided mixed model for repeated measurements). For NAAD (h,o), hash symbol marks that more than 85% of concentrations were below the LLOQ (0.02 µM) in the full dataset and the analysis was performed post hoc. All data in b–o are represented as boxes ranging from the upper to the lower quartile with the median indicated; error bars represent the minimum and maximum values. The number of data points (baseline/2 weeks or visit 3/visit 4) is indicated below each treatment. 0.01 < *_P_< 0.05; 0.001 < **_P_< 0.01; ***_P_< 0.001. Panel a created using BioRender.com.
The most prominent NAD+ boosters are Nam, nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), while the use of NA is limited by skin flushing and gastrointestinal (GI) symptoms at high dose. Although several studies have examined the acute and chronic effects of these precursors after oral administration, a head-to-head comparison of their impact on NAD+ levels in humans is lacking. Moreover, the oral bioavailability of polar and charged nucleotides and nucleosides similar to NR and NMN is notoriously poor, and recent studies in rodents suggest that a substantial part of the NAD+-boosting effect of NR and NMN is mediated via their microbial conversion to NA. Whether such gut microbial activities have a role in these precursor modes of action in a human clinical set-up remains elusive.
To compare the effects of the three NAD+ precursors NR, NMN and Nam versus placebo in healthy adults, a randomized, open-label, placebo-controlled four-arm study was conducted. The primary endpoint of the study was the change in the whole-blood baseline level of NAD+ after 14 days of once-daily dosing. The acute (in the 4-h period after supplementation) and chronic (from baseline on day 1 to baseline on day 14) effects on the NAD+ metabolome in whole blood were secondary endpoints. The NAD+ metabolomes in plasma and urine were exploratory endpoints. Additional exploratory endpoints included targeted and untargeted metabolomics in plasma and urine, respectively.
A total of 67 participants were enrolled in the study and randomized to receive a daily dose of an NAD+ precursor, NR (1 g d−1, 3.4 mmol d−1, n = 17), NMN (1 g d−1, 3 mmol d−1, n = 15) or Nam (0.5 g d−1, 4.1 mmol d−1, n = 17), or placebo (n = 18) for 14 days; CONSORT diagram. However, two individuals received the wrong test product throughout the entire study period (one in the placebo arm and one in the NR arm), and the modified intention-to-treat (ITT) analysis (n = 65) excluded these two individuals. All data reported below correspond to the modified ITT population who received the correct NAD+ precursor, NR (n = 16), NMN (n = 15) or Nam (n = 17), or placebo (n = 17). The baseline demographic characteristics of the participants are summarized. The mean age of the participants was 34.7 ± 7.4 years (32 males and 33 females) with a mean body mass index (BMI) of 21.4 ± 1.8 kg m−2 for females and 23.7 ± 1.8 kg m−2 for males.
The three NAD+ precursors were well tolerated. Only three adverse events with a probable relation to the product occurred during the study; out of the total 65 participants analysed, 1 participant in the placebo group reported abdominal pain, 1 in the NR group experienced hypotension and 1 in the NMN group had headache.
After 14 days, chronic administration of NR and NMN significantly increased baseline whole-blood NAD+ concentra
