Important up front: this was a mouse study. Nothing in it shows that nicotinamide riboside (NR) improves memory, slows brain aging, or reduces neuroinflammation in people. But in 22-month-old mice, eight weeks of NR changed both behavior and brain-cell gene activity in ways that looked strikingly youthful.
The paper, from Thiyagarajan and colleagues at the University of Kansas Medical Center and the VA Kansas City Healthcare System, appeared in GeroScience. Here is what they found and what it does and does not mean.
The Setup: Old Mice, a Popular NAD+ Booster
NR is a form of vitamin B3 that the body converts into NAD+, a molecule central to cellular energy and repair. NAD+ levels decline with age, which is why NR is one of the most popular longevity supplements.
Earlier work had shown that NR can restore NAD+ in aged mice. What remained unclear was how it affects microglia, the brain's resident immune cells, and cognition during normal aging rather than in a disease model.
The researchers compared three groups of mice:
- Young: 6 months old
- Aged: 22 months old
- Aged + NR: 22 months old, given NR at 400 mg/kg body weight for 8 weeks
The study used male mice only. The abstract does not report group sizes, so check the full paper for those numbers before drawing conclusions about statistical strength.
The Headline Finding: Behavior Improved
Aged mice did worse on cognitive tests and showed more neuroinflammation-related gene expression. NR "improved or prevented the decline" in three behavioral measures:
- Nest building, a proxy for instrumental activities of daily living
- Y-maze spontaneous alternation, a test of spatial working memory
- Novel object recognition, a test of recognition memory
The wording matters. The authors say NR improved or prevented the decline in these measures. That is not the same as a blanket claim that old mice became young again, and the abstract gives no effect sizes.
Under the Hood: Calmer Microglia and Astrocytes
The brain tissue results are where the paper gets interesting.
- IBA1 (a microglial activation marker) and GFAP (an astrocyte activation marker) were reduced with NR, "resembling the young phenotype."
- Gene expression profiling showed less microglial activation, fewer inflammatory pathways, and lower chemokine production in the Aged + NR group.
- Genes tied to learning, memory, and gliogenesis were upregulated.
- NR lowered transcriptional signatures of age-dependent (ADEM) and disease-associated (DAM) microglia, and strengthened homeostatic (healthy baseline) profiles.
DAM microglia are a state linked to neurodegeneration research, so seeing that signature fall is notable. The result is a shift in gene expression patterns, though, not proof that disease risk dropped.
The Metabolic Twist: Fat Metabolism in Microglia
Metabolic pathway analysis suggested that aging increased fatty acid metabolism in microglia, and NR suppressed that increase. Immunostaining supported this: lipoprotein lipase (LPL), a DAM marker, was reduced in the cortex and hippocampus of NR-treated mice.
The authors conclude that NR "appeared to mitigate" age-related cognitive decline by moving microglial gene expression and metabolism toward a younger profile. That is a hypothesis-generating framing, not a proven mechanism.
Limitations: Read Before You Get Excited
- Mice, not humans. Rodent brain aging does not map cleanly onto human cognitive decline.
- A very high dose. 400 mg/kg is far above what people take. This article does not offer a human-equivalent dose, and you should not try to calculate one from this study.
- Males only. Results may differ in females.
- Short duration. Eight weeks says nothing about long-term effects or safety.
- Correlation within a mechanism story. Gene expression and marker changes alongside better behavior suggest a link, but the abstract does not show that microglial changes caused the cognitive gains.
- Normal aging, not disease. The study does not address Alzheimer's or other dementias.
On the positive side, the authors declare no competing interests.
Practical Takeaways
Dose: There is no human dose to take from this study. For context, human NR trials typically use about 300 to 1,000 mg per day, but those trials have not established that NR prevents or reverses cognitive decline. The mouse dose should not be used to guide supplementation.
Timing: The study tested an eight-week course in mice. It offers no evidence on time of day, cycling, or optimal duration in humans.
Who might be interested: Healthy adults curious about NAD+ biology, and researchers and clinicians following geroscience. If you take NR already, this paper is a reason for cautious interest, not a reason to raise your dose.
Who should skip or check with a doctor first (general caution, not from the paper): People who are pregnant or breastfeeding, those on prescription medications, anyone with a cancer history or a serious medical condition, and anyone considering NR as a substitute for evaluation of memory problems. If you or a relative has noticeable cognitive decline, see a clinician rather than relying on a supplement.
The Bottom Line
In aged male mice, NR was associated with better nest building, working memory, and recognition memory, along with calmer, younger-looking microglia and less of the fat-metabolism signature linked to disease-associated states. It is an encouraging, mechanistically detailed preclinical result. Whether it translates into meaningful brain benefits in people is a question only well-designed human trials can answer.
