# NAD Supplement Research: What the Studies Measured | NAD+ > NAD supplement research, summarized: NAD+ is sold as a dietary supplement, usually as the precursors NMN or NR. What human trials measured, what stays unproven, and the regulatory picture. Cited. NAD+ is sold as a dietary supplement, not an approved drug — and most products deliver a precursor, not NAD+ itself. A cited reading of the human trials and the open questions. ## The short version NAD supplement research is mostly research on *precursors*. NAD+ (the cell's energy-handling helper molecule) is poorly absorbed when swallowed, so the products studied are usually NMN or NR (building blocks the body converts into NAD+). In trials, these reliably raised the amount of NAD+ in the blood, and the higher the dose the bigger the rise. What is far less settled is whether that blood-level change produces a meaningful health benefit in people. This page reports only what specific cited studies measured — it is not a recommendation to take any supplement. ## What a NAD supplement actually contains The phrase "NAD supplement" covers several distinct molecules. Plain NAD+ is sold, but because the intact coenzyme is large and charged, it is not efficiently taken up by cells, and most researchers consider precursors the rational oral approach [7]. The common precursors are NMN, NR, and the vitamin-B3 forms niacin and nicotinamide. NR reaches host NAD+ in part through an unexpected route: isotope tracing in mice showed gut bacteria convert NAD+ precursors, cycling them between the microbiome and host tissues [12]. This is why a label matters. The strongest human pharmacokinetic data are for NR and NMN capsules and powders, not for plain "NAD+" pills, patches, or sublingual formats, which carry little controlled evidence. This site does not name or endorse any commercial brand; the research is summarized by molecule, not by product. ## Why anyone supplements at all The rationale rests on one observation: tissue NAD+ declines with age across model organisms and humans [5]. Part of that decline is active consumption — the ectoenzyme CD38 rises with age and inflammation and eats into the NAD+ pool, and in mice deleting CD38 preserved NAD+ levels and mitochondrial function with age [2]. Because the cell continuously recycles NAD+ through the salvage pathway (rate-limited by the enzyme NAMPT), supplying more raw material — a precursor — is the mechanistically obvious lever [5]. That is the *hypothesis* a NAD supplement is built on. It is well supported as biochemistry. Whether feeding the pathway in a healthy adult produces a benefit they can feel or measure clinically is the separate, less-settled question the trials below were designed to probe. ## What the controlled trials genuinely show Two findings are solid. NR raised whole-blood NAD+ by 22%, 51%, and 142% at 100, 300, and 1000 mg/day over 8 weeks in healthy overweight adults, without elevating LDL cholesterol or disrupting one-carbon metabolism [4]. NMN at 300-900 mg/day for 60 days raised blood NAD+ at all doses versus placebo in a multicenter RCT, with 600 mg/day flagged as optimal and no safety issues at any dose [3]. Functional benefit is where the evidence thins. NMN at 250 mg/day for 10 weeks improved muscle insulin sensitivity in prediabetic postmenopausal women, but body composition and HbA1c were unchanged [1]. Much of the strongest anti-aging data come from rodents and may not extrapolate to humans [7]. A 2025 Nature Metabolism review concluded that human efficacy for hard clinical endpoints remains preliminary and that age-related NAD+ decline has been confirmed in only a limited number of human studies [15]. ## Does NAD make you look younger? Tissue NAD+ declines with age, and topical nicotinamide has been studied for skin aging and pigmentation, where it replenished the cellular NAD+ pool and reduced progression of skin aging in clinical trials [13]. But no trial in this corpus shows that an oral NAD+ precursor reverses visible aging. The strongest rejuvenation data come from rodent models [7], and the 2025 review found human anti-aging endpoints largely unproven [15]. ## The regulatory picture NAD+ and its precursors are sold as dietary supplements; none is an FDA-approved drug for any disease. The status of one precursor is contested: the FDA has taken the position that NMN is excluded from the dietary-supplement definition because it was authorized for investigation as a drug, which has created marketplace uncertainty. This is a regulatory dispute over how NMN may be marketed, not a finding that NMN is banned or unsafe. Supplement-grade products also vary in purity and actual content, and third-party testing is not guaranteed. None of this is medical or purchasing guidance — it is context for reading the literature. For administration routes and clearance, see [the doses used in the research](/dosage). --- A color-coded poster wall of the NAD+ record — the coenzyme, its oral precursors NMN and NR, and the thin IV-therapy evidence each set in its own block and cited to the study that measured it, with the precursor-not-NAD+ distinction kept exact; no clinic behind the wall and nothing here dosed, compounded, prescribed, or sold.