“My hair has lost volume.” “It no longer feels as strong or glossy.” “I am concerned about shedding.” Changes like these are common concerns with aging. Because hair strongly influences appearance, age-related changes can have a meaningful effect on self-perception.
One biological factor being studied in this context is NAD+, a coenzyme whose levels decline with aging, together with its precursor NMN, or nicotinamide mononucleotide. Previous articles have explained why NAD+ is important, how NMN may increase NAD+, and research on NMN in cognitive function and oocyte quality.
Although oral NMN had previously been associated with changes in skin hydration and elasticity2, no clinical study had examined human hair. The study reviewed here tested oral NMN in middle-aged women. According to the researchers, it was the first clinical study of NMN and human hair, and it was published in Cosmetics in 20253.
What You Will Learn
- How aging may affect hair through the hair cycle and declining NAD+
- Why sirtuins and mitochondria are relevant to NMN research on hair
- The design and findings of a 12-week study involving 15 middle-aged women
- The study’s significance, limitations, and points requiring caution
Why Hair Changes With Aging: The Hair Cycle and NAD+
Hair follows a rhythm known as the hair cycle, which consists of anagen, catagen, and telogen phases. Healthy hair grows longer and thicker during anagen. Aging, stress, and poor nutritional status may disrupt this cycle, contributing to thinner hair and lower volume.
- Hair cycle
- The repeating sequence of anagen, when hair grows actively; catagen; and telogen. Disruption of this cycle with aging or other factors may contribute to hair thinning.
Maintaining the hair cycle requires active function in the cells that produce hair. The coenzyme NAD+, which supports cellular metabolism, declines with aging1 and has therefore been proposed as one factor relevant to age-related hair changes.
- Coenzyme
- A substance that assists an enzyme in carrying out a biochemical reaction.
Why NMN Is Being Studied in Hair: Sirtuins and Mitochondria
NMN can increase NAD+ availability, potentially supporting mitochondrial energy production, DNA repair, and antioxidant defenses. Researchers have asked whether these systemic biological effects might extend to hair follicles.
- Mitochondria
- Cellular structures that produce energy in the form of ATP.
Studies in mice and cultured cells had reported that NMN reduced hair-follicle atrophy and inflammation in dermal papilla cells induced by the androgen DHT4. However, these effects had not been tested in human hair. The research team therefore examined oral NMN in middle-aged women who commonly experience age-related hair concerns.
- DHT, or dihydrotestosterone
- An androgen implicated in androgenetic hair loss.
- Hair follicle
- A sac-like structure in the skin that produces and supports hair. Dermal papilla cells at its base regulate hair growth.
Study Overview: Oral NMN for 12 Weeks in 15 Middle-Aged Women
The 2025 study in Cosmetics examined how oral NMN influenced hair characteristics and related metabolic measures in healthy Japanese women with hair concerns3.
Study Design
- Participants: 15 healthy Japanese women in their 40s and 50s who reported concerns such as thinning hair or reduced strength and gloss
- Intervention: Oral NMN at 500 mg/day for 12 weeks; a single-arm, open-label study without a placebo group
- Hair assessment: Hair density measured with TrichoScan and hair diameter and surface structure observed by scanning electron microscopy, or SEM
- Molecular and hormonal assessment: Hair metabolomics and measurement of hormone concentrations in hair
- Subjective assessment: Visual analogue scales, or VAS, for fatigue and perceived hair characteristics
- Single-arm, open-label study
- A trial without a comparison group in which all participants receive the same intervention and both participants and researchers know what is being given.
- TrichoScan
- A system that photographs the scalp and analyzes hair density, thickness, and growth stage.
- Scanning electron microscopy (SEM)
- A microscopy method used to examine surfaces at high magnification.
- Metabolomics
- Comprehensive measurement of metabolites within a sample.
- VAS
- A visual analogue scale that converts a subjective sensation into a numerical score by marking a point along a line.
Study Results
1. Growth of Anagen Hairs Increased
After 12 weeks of NMN, the number of growing anagen hairs measured three days after shaving increased significantly from 55.9 to 87.7 hairs/cm², with p = 0.03. The increase was particularly large among terminal hairs at least 40 µm in diameter, which rose from 38.6 to 66.2 hairs/cm², with p < 0.01.
2. Hair Diameter Increased and Cuticle Appearance Changed
SEM measurements showed that mean hair diameter increased significantly from 75.3 µm to 78.8 µm, with p < 0.01. Hair became thicker in 11 of the 13 participants included in this analysis. The condition of the cuticle covering the hair surface also improved according to the study’s assessment. Together with the anagen-growth findings, these changes were interpreted as a shift toward thicker, more robust hair.
- Cuticle
- The scale-like outer layer covering the hair shaft. A smooth, aligned cuticle contributes to gloss and texture.
3. Changes in Hair Metabolites Related to Amino-Acid and Energy Metabolism
Hair metabolomics showed significant increases in amino acids including tryptophan and glutamate and in energy-related metabolites including creatine and carnitine. Lactate declined. The research team interpreted these changes as potentially consistent with increased mitochondrial energy production and amino-acid metabolism.
NMN and NAD+ themselves remained below the assay’s detection limit in hair. Some NMN-related metabolites, including nicotinamide riboside, were detected in some participants after supplementation.
4. No Clear Change in Hair Hormone Concentrations
Concentrations of cortisol, testosterone, and progesterone in hair did not change significantly from baseline. The researchers suggested that high individual variability, the small sample, and the short intervention period may have made hormonal changes difficult to detect.
5. Subjective VAS Scores for Hair Characteristics and Fatigue Changed
Participants’ VAS ratings showed significant improvements in perceived hair strength, ease of combing, gloss, and volume. Ratings related to concern about gray hair, visibility of the hair part, perceived shedding on waking or during shampooing, and fatigue also improved, all with p < 0.01.
The direction of these subjective changes was consistent with some of the objective hair measurements. However, because the study had no placebo control and participants knew they were taking NMN, expectation effects cannot be excluded.
Discussion: How Might NMN Affect Hair?
Interpreting the Decline in Total Hair Count
Despite the positive findings above, total hair count declined after supplementation. The research team could not rule out an effect of NMN, but proposed that seasonal shedding may have contributed because the study ran from September to December, following summer ultraviolet exposure5. Previous research in Japanese participants has reported increased shedding around September.
Because total hair count declined while growth of thicker anagen hairs increased, the authors proposed that NMN may have supported the growth of existing terminal hairs rather than producing new fine hairs. This interpretation remains provisional.
Possible Roles of Sirtuins and Mitochondria
The researchers proposed that sirtuins, NAD+-dependent proteins involved in metabolism and aging, and mitochondrial function may contribute to the findings. Animal studies have reported that increasing NAD+ can activate hair-follicle stem cells and support hair growth and that sirtuins participate in hair-cycle progression46. The observed changes in amino-acid and energy-related metabolites were considered consistent with these pathways.
- Sirtuins
- A family of NAD+-dependent proteins involved in metabolism, stress responses, and aging-related biology.
Fatigue and Subjective Satisfaction
Fatigue ratings improved alongside perceived hair characteristics. The authors proposed that increasing NAD+ might support mitochondrial function and basal metabolism, reducing fatigue and indirectly improving perceptions of hair. This interpretation is based on subjective measures, and the mechanism remains uncertain.
Study Position and Limitations
This was an early report examining NMN and human hair. Its limitations are substantial: only 15 participants were enrolled; there was no placebo group; participants and researchers were unblinded; the intervention lasted only three months; and seasonal effects may have influenced shedding.
The results cannot be generalized beyond the population studied—middle-aged Japanese women. Larger, longer, placebo-controlled trials are needed to determine whether the findings are reproducible and attributable to NMN.
Practical Foundations for Hair Health
Although this research is preliminary, established aspects of general hair care remain relevant.
- Limit ultraviolet exposure: The authors suggested that summer UV damage may have contributed to autumn shedding5. Hats and parasols can reduce UV exposure to the scalp and hair.
- Consume adequate nutrients used to build hair: Hair is composed largely of protein. The study also reported changes in amino-acid and energy-related metabolites in hair. Dietary protein from foods such as meat, fish, eggs, and soy supports normal hair production.
- Support energy metabolism through general health habits: NAD+, which participates in cellular energy metabolism, is influenced by aging and broader physiological factors. Adequate sleep and moderate exercise support whole-body energy metabolism.
Research on NMN and hair has only begun. These findings should not replace established care. Sudden or progressive hair loss warrants consultation with a dermatologist or another qualified healthcare professional.
Summary
- Age-related hair changes may involve disruption of the hair cycle and declining NAD+.
- In this study, 15 middle-aged women took 500 mg/day of NMN for 12 weeks. Growth of anagen hairs and mean hair diameter increased significantly from baseline.
- Hair metabolomics showed changes in amino-acid and energy-related compounds, while subjective ratings of strength, gloss, volume, and fatigue improved.
- Total hair count declined, possibly because of seasonal shedding, and hormone concentrations did not change significantly.
- The study was small, single-arm, and open-label. Larger, long-term, placebo-controlled trials are required before an effect can be established.
Important Considerations
This article summarizes recent research and does not recommend a specific supplement or claim that it produces particular effects. The study was a small, uncontrolled early clinical investigation and does not guarantee benefits for hair or general health. Consult a healthcare professional when appropriate.
References
- Chu, X.; Raju, R.P. Regulation of NAD+ Metabolism in Aging and Disease. Metabolism. 2022. ↩
- Morita, Y. et al. Clinical Evaluation of Changes in Biomarkers by Oral Intake of NMN. Glycative Stress Res. 2022. ↩
- Fukumoto, S. et al. Oral Supplementation of Nicotinamide Mononucleotide (NMN) Improves Hair Quality and Subjective Perception of Hair Appearance in Middle-Aged Women. Cosmetics. 2025; 12(5): 204. ↩
- Xu, C. et al. β-Nicotinamide Mononucleotide Promotes Cell Proliferation and Hair Growth by Reducing Oxidative Stress. Molecules. 2024; 29: 798. ↩
- Kita, F. et al. Evaluation Method of the Hair Growth Promoter Based on Dynamics of Fall Hairs. Skin Res. 1989. ↩
- Li, G. et al. SIRT7 activates quiescent hair follicle stem cells to ensure hair growth in mice. EMBO J. 2020. ↩
