NAD+ Supplements Raise Blood Levels, But Clinical Benefits Remain Uncertain

Why this matters: NAD+ and its relatives NADH, NADP+ and NADPH underpin mitochondrial energy production, antioxidant defense, DNA repair, and the activity of sirtuins, PARPs, and CD38. NAD+ decline is widely described as a hallmark of aging and is implicated in cognitive decline, depression-related phenotypes, Alzheimer's disease, and Parkinson's disease. This has fueled strong consumer and clinic interest in NAD+ precursors and intravenous NAD+ infusions, even though the evidence for benefit is uneven.

What was studied: This narrative review combines a literature search with a mathematical modelling framework. The authors searched PubMed, Scopus, and Web of Science using terms such as NAD with clinical efficacy, supplementation, cognition, and neurodegenerative disorder. PubMed alone returned roughly 580 to 1,600 items per query. They then summarized recent preclinical work since 2020 in a table. The full text available for this summary was cut off partway through the preclinical section, so the modelling methods and quantitative results could not be checked directly. Only the abstract's description of them is reported here.

Key results: The most consistent human finding is biochemical. NR and NMN repeatedly raise circulating NAD+ or NAD-related metabolites, and acute MRS studies suggest NR can raise brain NAD+. Clinical efficacy is variable. The clearest disease-specific benefit is in mitochondrial myopathy, where niacin corrected systemic NAD+ deficiency and improved muscle performance. NMN improved muscle insulin sensitivity in postmenopausal women with prediabetes, while other NMN trials showed higher blood NAD+ and modest physical-performance signals without broad metabolic change. In Parkinson's disease, the NADPARK trial showed NR enhanced cerebral and systemic NAD metabolome signatures but was not designed to show disease modification. In mild cognitive impairment, NR raised blood NAD+ without clearly improving cognition. Preclinical work points to CD38-positive inflammatory cells as drivers of age-related tissue NAD+ loss. CD38 inhibition (78c) improved healthspan-related outcomes in aged mice. NMN restored oocyte quality in aged mice, and NR or NMN improved kidney injury models by limiting mitochondrial RNA-driven inflammation. At least one study found minimal metabolic effects of NR in mild obesity.

Implications: The authors conclude that NAD+ responses are nonlinear rather than a simple dose-response, shaped by dose, age, metabolic state, route, feedback regulation, and biological saturation. Tissue-specific enzymes such as purine nucleoside phosphorylase may also route precursors differently. Preserving NAD+ may require limiting consumption (for example by inhibiting CD38) as well as supplying precursors. Patients with demonstrable NAD+ deficiency may respond best.

Caveats: Intravenous NAD+ is less well characterized and lacks robust clinical validation, and optimal dose, frequency, and long-term safety remain undefined. The literature is dominated by reviews and preclinical studies, with few adequately powered randomized trials and substantial heterogeneity in compound, dose, duration, and endpoints. The authors state that NAD+ supplementation is promising but not yet proven as a general anti-aging or neuroprotective therapy.