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Supplements

Nicotinamide Riboside Doubled NAD+ but Failed to Boost Memory

Nova Chen · · 4 min read
#supplements #clinical trial #nad+ #nicotinamide riboside #mild cognitive impairment #alzheimers #cerebral blood flow

The Number Looked Great. The Memory Results Didn't.

Imagine a supplement that does exactly what the label promises. It doubles the level of a molecule your cells depend on. Then you check whether it helped the thing people actually buy it for, and the answer is no.

That is roughly what happened in a new phase-II pilot trial of nicotinamide riboside (NR) in older adults with amnestic mild cognitive impairment (aMCI). The study was led by Martens and colleagues and published in Alzheimer's & Dementia in 2026. Blood NAD+ rose twofold, but cognition did not improve.

What the Researchers Did

The team ran a 12-week, double-blind, randomized, placebo-controlled pilot study. They wanted to know whether NR, a precursor of NAD+, could improve cognitive function and cerebral blood flow (CBF) in adults with aMCI. aMCI is a memory-focused form of mild cognitive impairment that carries elevated risk of progressing to Alzheimer's disease.

The rationale is a popular one. NAD+ is central to cellular energy metabolism, and the study's introduction notes that declining NAD+ may raise the risk of Alzheimer's disease. If you can restore NAD+, the thinking goes, you might protect the aging brain.

Forty-two participants completed the trial: 22 in the NR group and 20 on placebo.

The Results at a Glance

  • Blood NAD+: Increased about twofold in the NR group. The supplement did what it was supposed to do biochemically.
  • Cognitive function (primary outcome): No improvement.
  • Total cerebral blood flow (secondary): No improvement.
  • Blood pressure (secondary): No improvement.
  • Safety and adherence: Adherence was similar between groups, and there were no serious adverse effects.

The authors' conclusion is plain: NR effectively raises NAD+ in people with MCI but does not improve cognitive function, total CBF, or blood pressure over 12 weeks.

The Hippocampus Hint (Handle With Care)

There was one intriguing wrinkle. Exploratory analyses suggested potential increases in regional cerebral blood flow, particularly in the hippocampus, a region closely tied to memory and among the first affected in Alzheimer's disease.

This is not a win. Exploratory analyses are hypothesis-generating by design. They were not the primary outcome, and with a small sample, such signals can easily appear by chance. The authors say only that future studies should investigate regional CBF effects over longer treatment durations. It is a reason to keep looking, not a reason to buy.

Why Raising NAD+ Isn't the Same as Fixing the Brain

This trial is a useful reminder that a biomarker moving is not a clinical outcome improving. Doubling blood NAD+ shows the compound was absorbed and metabolized. It does not show that the change reached the brain in a meaningful way, or that low NAD+ was the bottleneck in these participants' cognitive decline.

Mild cognitive impairment is also driven by many overlapping processes, including protein accumulation, vascular changes, and inflammation. A single metabolic precursor may simply not be enough to shift those over 12 weeks.

Honest Limitations

Before anyone over-reads this study in either direction, consider what it can and can't tell us:

  • It's a pilot. With 42 completers, the study was built to assess safety, tolerability, and preliminary efficacy, not to settle the question.
  • 12 weeks is short. Cognitive decline in aMCI is slow. A longer trial might show effects this one couldn't, or might not.
  • One population. The results apply to older adults with aMCI. They don't tell us about healthy adults, younger people, or other conditions.
  • Exploratory findings are tentative. The hippocampal blood flow signal needs confirmation.
  • A negative result is not proof of no effect. Small trials can miss modest benefits, though the lack of any signal on the primary outcome is worth taking seriously.

Practical Takeaways for Buyers

What NAD+ boosters can do: In this trial, NR reliably raised blood NAD+ and was well tolerated, with no serious adverse effects.

What this study doesn't show: It gives no evidence that NR improves memory, thinking, total brain blood flow, or blood pressure in people with aMCI over 12 weeks.

Dose and timing: The abstract doesn't specify the dose, and the trial wasn't designed to test timing. Check the full paper for the exact regimen before drawing comparisons. Commercial NR products vary widely in dose, and nothing here supports a particular dose or time of day for a cognitive benefit.

Who it's (not) for: If you or a relative has memory concerns, this study gives no reason to treat NR as a substitute for medical evaluation, proven lifestyle measures, or approved care. Anyone with MCI or on other medications should talk to a clinician before starting supplements.

Marketing red flag: Be skeptical of any product that cites "increased NAD+" as proof of brain benefits. This trial shows those are separate claims.

The Bottom Line

NR passed the biochemistry test and failed the memory test, at least over 12 weeks in a small group with aMCI. The hippocampal blood flow hint keeps the door open for longer, larger studies. For now, the honest message is that NAD+ boosters can raise NAD+, and whether that translates into a better brain is still unproven.

Source: Martens et al. A phase-II randomized controlled pilot study of nicotinamide riboside supplementation in older adults with amnestic mild cognitive impairment. Alzheimers Dement. 2026. DOI: 10.1002/alz.71605 | PubMed 42478598

Original study

Read the original research on pubmed.ncbi.nlm.nih.gov →

This article summarizes published research for general information. It is not medical advice.

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Written by

Nova Chen

Nova Chen writes for Biocracked: biohacking science, longevity & human performance.

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