NAD+ boosting & Alzheimer's — preclinical vs null

Alzheimer's research has a recurring problem: treatments that work brilliantly in mice often fail in people. NAD+ boosting is a sharp example of that gap, and the human trial data are now clear enough to address directly.

What the mouse research showed

Alzheimer's brains have a measurably low NAD+/NADH ratio, the balance between the oxidized and reduced forms of this critical metabolic cofactor. In a 2018 study by Hou and colleagues, raising NAD+ levels in mouse models normalized DNA damage and reversed memory deficits [1]. Those are striking results. In the Alzheimer's research world, "reversal" in an animal model generates real excitement, and for a period it did exactly that.

The biological rationale held together: NAD+ is central to DNA repair, mitochondrial function, and the activity of sirtuins, a class of proteins involved in cellular stress responses. If Alzheimer's pathology depletes NAD+ and restoring it rescues cognition in mice, oral precursors like nicotinamide riboside (NR), nicotinamide mononucleotide (NMN), or plain nicotinamide seemed like plausible candidates for human trials.

What happened in human trials

Human trials of NAD+ precursors in Alzheimer's disease and mild cognitive impairment have not replicated the animal findings. Clinical trials of NR, nicotinamide, and NMN in AD and MCI populations showed no cognitive benefit [2]. Not a marginal or ambiguous signal, null.

This is a meaningful distinction. Mouse models of Alzheimer's are genetically engineered to accumulate amyloid rapidly, and the "reversal" seen in those models does not map onto the slower, more heterogeneous disease process in humans. Verhoeven's analysis suggests the preclinical actor in those experiments may have been direct NAD+ delivery or novel injection routes, not the oral precursors currently available as supplements [3]. Oral NR or NMN raise circulating NAD+ metabolites in blood, but whether that translates into meaningful changes in brain NAD+ remains unresolved.

MCT oil and ketones: a more modest story

One adjacent intervention has produced at least some signal in humans. Medium-chain triglycerides (MCTs) provide the liver with substrate to produce ketones, which the brain can use as an alternative fuel when glucose metabolism is impaired, as it is in Alzheimer's. Trials of MCT supplementation show modest, inconsistent cognitive benefit [4]. The effect is not uniform across patients: benefit appears more likely in people who do not carry the APOE4 allele, the genetic variant that most strongly raises Alzheimer's risk. This is not a reversal of disease. It is a modest metabolic support strategy with real limitations.

Verhoeven's analysis suggests he reads the overall evidence as pointing down on NAD+ supplements for Alzheimer's and cautiously positive on MCTs [3], a position consistent with the primary trial record as it stands.

Framing what "reversal in mice" means

Language matters here. The Hou 2018 findings describe complete reversal of memory deficits in a mouse model [1]. That finding is real and worth continued investigation. It does not mean NAD+ supplements reverse Alzheimer's in humans. No human data support that claim. Anyone citing the mouse work to justify NAD+ supplementation for cognitive protection or Alzheimer's treatment is extrapolating well past what the evidence currently shows.

The research frontier worth watching involves adequately powered human RCTs with NAD+ precursors, and particularly any trials exploring direct delivery routes that bypass the conversion steps oral supplements depend on. Those trials have not yet been conducted at scale.

Where the evidence is contested

The core disagreement is not about the mouse data, which are broadly accepted, but about what follows from them.

One position holds that the human null results reflect inadequate trial design: doses may have been too low, durations too short, or patient populations too heterogeneous to detect a real effect. If brain NAD+ was not meaningfully raised in those trials, the negative results do not rule out the mechanism.

The opposing position holds that null results in multiple human trials with different precursors constitute meaningful evidence against the therapeutic hypothesis as currently practiced with oral supplements. The mechanistic gap between raising blood NAD+ metabolites and rescuing Alzheimer's cognition in humans is large enough that optimism requires substantial new evidence, not extrapolation from mice.

Both positions are represented in the research literature. No adequately powered human RCT has yet tested the intervention in a form that would fully resolve the question [2].

References

1. Hou/Fang 2018, PNAS — NAD+ normalizes AD (mouse)
2. Nicotinamide riboside in MCI — RCT (null cognition)
3. raw/physionic/nad-nmn/01-nad-boosting-reverses-alzheimers.txt
4. MCT/ketones & AD cognition — meta-analysis · PubMed 31870908