NAD+ for Hair Growth: Two Real Studies, One Blurred Claim
Published by AmpleLab Research
NAD+ (via NMN or NR supplementation) is one of the biggest topics in longevity and biohacking content, and it's increasingly discussed as a way to reverse hair aging by regenerating hair follicle stem cells. There are two real, legitimate studies behind this claim. The problem is that they're being merged into one story neither of them individually tells.
This article separates the two studies, what each actually did, and where the gap is between them.
Study One: SIRT7 Genuinely Activates Hair Growth in Mice
SIRT7 is NAD+-dependent, meaning it requires NAD+ as a cofactor to function, but this study did not test whether increasing NAD+ levels through supplementation would increase SIRT7 activity in follicles; it tested what SIRT7 itself does when directly manipulated. SIRT7 was found to directly control whether hair follicle stem cells exit dormancy and re-enter the growth (anagen) phase. Sirt7 expression declines in hair follicles with age. In mice, knocking out Sirt7 delayed hair regrowth, while overexpressing it accelerated the shift from resting to growing follicles. Aged mice with reinforced Sirt7 showed faster hair regrowth after plucking and higher hair shaft density than untreated aged mice, even at 28 months old. Mechanistically, SIRT7 deacetylates a protein called Nfatc1, triggering its breakdown and ending the follicle's dormant phase.
The key detail: this was achieved through genetic manipulation, engineering mice to overexpress the Sirt7 gene directly. It tells us SIRT7 activity genuinely matters for hair growth cycling. It does not tell us that raising NAD+ levels through supplementation would boost SIRT7 activity enough to produce the same effect; that's a separate, untested step.
Study Two: NAD+ Supplementation Protected a Different Cell Population
This is the actual supplementation study behind the NAD+ hair narrative, and it's a well-known, highly-cited paper. Aged mice were fed nicotinamide riboside (NR), an NAD+ precursor. NR protected muscle stem cells from age-related decline, extended lifespan modestly, and, relevant here, delayed senescence in neural stem cells and melanocyte stem cells specifically.
The key detail: melanocyte stem cells govern hair pigmentation, not hair growth. They live in the same follicle structure as the growth-cycling stem cells covered in the SIRT7 study above, but they're a distinct population with a different job: colour, not cycling. This study didn't measure hair growth, density, or the follicle stem cells that actually drive the growth cycle. Its relevance, if any, would be to greying rather than thinning.
Where the Claim Actually Gets Blurred
Both studies involve NAD+ biology, both involve cells that live inside a hair follicle, and both come from serious, well-cited research. That's enough surface similarity for secondary sources to merge them into a single, tidier story: "NAD+ regenerates hair follicle stem cells and promotes hair growth." Read closely, neither study actually says that. The study that demonstrates a genuine hair-growth effect (SIRT7) didn't test NAD+ supplementation, it used direct genetic manipulation. The study that tested actual NAD+ supplementation (NR) didn't test hair growth or the growth-cycling stem cells, it tested a different cell population responsible for pigment.
The missing link, whether raising NAD+ through supplementation actually increases SIRT7 activity enough in human hair follicle stem cells specifically to meaningfully affect the anagen-telogen cycle, covered in more depth in our article on the hair growth cycle, hasn't been tested. It's a reasonable hypothesis connecting two real findings, not a demonstrated result.
The honest position
SIRT7, an NAD+-dependent enzyme, genuinely controls hair follicle stem cell activation in mice, a real and well-documented finding. Separately, NAD+ supplementation via NR genuinely protects certain aged stem cell populations in mice, also real, but the specific population shown to benefit governs hair colour, not hair growth, and hair growth itself wasn't measured. No study has tested whether NAD+ supplementation activates the growth-relevant SIRT7 pathway in hair follicles specifically, in mice or in humans. The individual pieces are real science; the combined claim is an inference that hasn't been tested.
Frequently Asked Questions
Does taking NMN or NR regrow hair?
This hasn't been tested. The mouse study on NAD+ supplementation (NR) didn't measure hair growth; it looked at a different stem cell population responsible for pigmentation. The study that did show a real hair-growth effect used genetic manipulation of SIRT7, not supplementation.
Is the SIRT7 hair growth study real?
Yes, published in The EMBO Journal in 2020, a well-regarded peer-reviewed journal. It's a genetic mouse study, not a supplementation study, so it establishes that the pathway matters, not that taking an NAD+ precursor activates it sufficiently.
What's the difference between melanocyte stem cells and hair follicle stem cells?
Both reside within the hair follicle, but they do different jobs. Melanocyte stem cells produce the pigment that gives hair its colour; their decline is associated with greying. Hair follicle (epithelial) stem cells drive the growth cycle itself, whether a follicle is actively growing or resting. The widely-cited NR supplementation study affected the pigment-related population, not the growth-cycling one.
Has this been tested in humans at all?
Not for hair. Both studies discussed here are mouse research. We're not aware of a human trial testing NAD+ precursor supplementation for hair growth or density specifically.
References
This article is provided for educational purposes and does not constitute medical advice. AmpleLab products are cosmetic formulations and are not intended to diagnose, treat, cure, or prevent any condition.
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