# NAD+: Clinical Research Digest — IV Protocols, Precursor Trials, and Mechanism

> NAD+ drives mitochondrial ATP synthesis, sirtuin-mediated gene regulation, and PARP1 DNA repair. Blood levels decline roughly 50% by age 60. A clinical-facing digest of the peer-reviewed evidence.

## What the NAD+ literature has established

NAD+ — nicotinamide adenine dinucleotide — is present in every living cell. It is the primary electron carrier in glycolysis and the TCA cycle, the required substrate for sirtuins (SIRT1–7) that regulate gene expression and mitochondrial biogenesis, and the fuel consumed by PARP1 at every DNA strand break [13]. These three functions are not separate: each one depletes the same cellular NAD+ pool.

Across human biopsy studies, blood NAD+ and NAD+ in skin tissue fall measurably with age, and PARP activity rises in inverse proportion [22]. In mouse genetic models, CD38 NADase expression increases 2–3-fold across multiple tissues during chronological aging; knocking out CD38 preserved mitochondrial function and SIRT3 activity in aged mice [1]. A subsequent study identified senescent cells as an upstream cause: their inflammatory secretions activate CD38-expressing macrophages in liver and visceral fat, accelerating the drain [2].

Blood NAD+ elevation by oral NMN and NR is now well-documented across at least eighteen completed human trials. Skeletal muscle insulin sensitivity improved significantly in a Washington University RCT of NMN in postmenopausal women with prediabetes [5]; walking distance and VO₂max improved with NMN in middle-aged adults [6, 17]; grip strength and gait speed improved in older men at 250 mg/day for 12 weeks [7]. Cognitive outcomes in mild cognitive impairment did not improve despite confirmed NAD+ elevation [20].

IV NAD+ administration achieves plasma elevations orders of magnitude above oral dosing. A pharmacokinetic pilot study characterized the plasma and urine NAD+ metabolome during a 750 mg IV infusion in healthy males, establishing the first human IV NAD+ PK profile [9].

## NAD+ Benefits Documented in Clinical and Preclinical Research

The benefits documented in peer-reviewed research fall into four clusters:

**Energy metabolism and aerobic capacity.** NMN at 300–1200 mg/day combined with exercise improved VO₂max and ventilatory thresholds dose-dependently in middle-aged amateur runners [17].

**Skeletal muscle insulin sensitivity.** NMN at 250 mg/day for 10 weeks significantly increased skeletal muscle insulin-stimulated glucose disposal in postmenopausal women with prediabetes vs placebo (Yoshino et al. 2021, Science) [5]. Liver insulin sensitivity was unchanged.

**Physical function in older adults.** A 12-week RCT of 250 mg/day oral NMN in healthy older men showed significant improvements in gait speed (p=0.033) and left-hand grip strength (p=0.019) [7].

**DNA repair and rare aging diseases.** NR supplementation in Werner syndrome patients (52-week RCT, n=9) produced a ~140% plasma NAD+ increase with improved arterial stiffness, HDL counts, and kidney function [21].

## How Does NAD+ Decline With Age?

Three mechanisms drive the age-related fall in tissue NAD+:

- **CD38 upregulation.** CD38 expression rises 2–3-fold with aging in mice; inflammatory SASP cytokines from senescent cells activate CD38-expressing macrophages, accelerating the drain [1, 2].
- **NAMPT decline.** The rate-limiting salvage pathway enzyme falls with age in skeletal muscle; exercise training restores NAMPT 12–30% [23].
- **PARP competition.** Severe DNA damage can deplete up to 90% of cellular NAD+. In aged human skin biopsies, PARP activity correlated inversely with NAD+ level [22].

## What Does NAD+ Do for the Body?

NAD+ is a coenzyme present in every cell, essential for ATP production via the mitochondrial electron transport chain, sirtuin-mediated gene regulation, and PARP1-dependent DNA repair. Levels decline approximately 50% between young adulthood and age 60 based on human tissue biopsy data [22].

NAD+ is not a peptide. It is a dinucleotide coenzyme — two nucleotides joined by a pyrophosphate linkage — with molecular formula C₂₁H₂₇N₇O₁₄P₂ and molecular weight 663.4 Da. It has no structural or pharmacological relationship to GLP-1 agonist compounds.

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Chrome-console readings of the peer-reviewed NAD+ record — clinical trials indexed, infusion rates logged, no prescriptions filled.