Why Your Hair is Aging (And The Science to Reverse It)

🔬 The science of hair aging - and how to reverse it. In this video, Dr. Hillary Lin, MD breaks down the complex biology behind hair loss, graying, and thi…

Published January 23, 2025The Longevity Show

A patient in her late thirties came to Dr. Lin about sudden thinning. The hair turned out to be the presenting sign rather than the problem — the workup surfaced perimenopause and nutritional deficiencies, and when those were treated the hair recovered along with her energy and mood. That is the argument for taking hair seriously in a longevity context: it is one of the most metabolically demanding tissues in the body, so it degrades early when something systemic is wrong.

The organising idea is that thinning and greying are the same problem expressed two ways. Both trace back to oxidative stress, hormonal shift and failing cellular energy — melanocytes lose the ability to make pigment, hair follicle stem cells lose the ability to regenerate, and the interventions that address one largely address the other. Dr. Lin walks the cycle first, since the phases explain what you are actually seeing: anagen, the 2-to-6-year growth phase holding about 85% of your hair; catagen, a two-week regression; telogen, one to four months of rest; and exogen, the shed.

The back half is a survey of what can be done, sorted by how much evidence sits behind it — nutrition, then the hormonal drugs with real effect sizes and real side effects, then the cellular interventions ranging from established to frankly experimental. Dr. Lin is notably even-handed about supplement trials funded by the companies selling the supplement, and she flags one thing as genuinely time-sensitive: once a follicle is gone there is nothing left to rejuvenate, which makes acting early a different kind of decision from most cosmetic ones.

Before you watch

The growth cycle explains most of what people misread as sudden loss. Anagen is the active growth phase lasting 2 to 6 years, holding roughly 85% of your hair at any time — and how long a follicle stays in it determines the length your hair can reach. Catagen is a two-week controlled regression, telogen a 1-to-4-month rest holding about 9% of follicles, and exogen the shed itself. Stress, hormonal shifts and nutritional gaps push follicles out of anagen early, which is why thinning often shows up months after the event that caused it.
DHT damages follicles through four separate mechanisms, which is why it is hard to counter. Derived from testosterone by 5-alpha-reductase, it binds androgen receptors on dermal papilla cells and drives follicular miniaturisation, arrests the cell cycle so anagen shortens, downregulates the Wnt/β-catenin pathway that follicle growth depends on, and activates TGF-β/SMAD signalling that accelerates shrinkage. The pattern of loss follows receptor density: temples and crown carry more androgen receptors, while the back of the head carries fewer — which is exactly why it serves as the donor site for transplants.
The cellular story runs through stem cells and the collagen holding them in place. Hair follicle stem cells drive regeneration, and type XVII collagen (COL17A1) maintains their resilience — DNA damage degrades COL17A1 and the stem cell population loses vitality with it. Mitochondrial decline compounds this by raising reactive oxygen species that damage both stem cells and melanocytes, and shortening telomeres cut the growth phase directly. Mouse work on stimulating telomerase, and on inhibiting CDC42 to reverse the age-related shift from regenerative Wnt to growth-inhibiting Wnt5a signalling, is early but mechanistically pointed.
Iron deficiency is one of the most common causes of hair loss, particularly in menstruating women, and Dr. Lin's dosing advice is not the default. Check levels before supplementing rather than after. She prefers ferrous bisglycinate as the more bioavailable form, and recommends taking it every other day rather than daily — daily dosing reduces your body's sensitivity to it, a point she also makes for patients supplementing iron for restless leg syndrome. Pairing iron-rich foods with vitamin C improves absorption.
Biotin has one practical trap almost nobody is warned about: it interferes with laboratory assays. If you have blood work coming up — an annual panel, a longevity workup — Dr. Lin advises pausing biotin supplements at least three days beforehand and possibly a week, because it can distort results enough to mislead both you and your physician. On the supplement itself she is measured: biotin is essential for keratin production and mild deficiency causes brittle or thinning hair, but more is not better.
Her vitamin D advice comes as a stack rather than a single nutrient. Take D3 specifically, since other forms require additional conversion. Add K2, which directs calcium into bone rather than leaving it in circulation where it can contribute to arterial calcification. And ensure adequate magnesium, without which the body cannot make use of the vitamin D you are taking. Vitamin D supports the hair cycle partly by inhibiting inflammatory pathways that would otherwise disrupt it.
Zinc is the one supplement she actively steers away from. It is easy to overdo, and her preference is to get it from whole foods rather than pills — a notable exception in an episode otherwise sympathetic to targeted supplementation.
On commercial hair supplements she models the right kind of skepticism rather than dismissal. Viviscal is built around a marine protein complex, AminoMar C; Nutrafol combines saw palmetto and ashwagandha to target hormonal and stress pathways; Pantogar, from Germany, uses amino acids, keratin and B vitamins. Her caveat applies to all three: trials on commercialised products are typically funded by the company selling them and should be discounted accordingly — but they are not automatically garbage, and a well-conducted study replicated in independent labs showing a clinically significant effect deserves some credence.
Two plant-derived interventions have specific numbers attached. Pumpkin seed oil, rich in phytosterols that may inhibit 5-alpha-reductase, produced a 40% increase in hair count over 24 weeks in one study of men — with the timescale being the point, since nutritional interventions take months. Tocotrienols, a form of vitamin E found in palm oil, rice bran oil and certain grains, have also been linked to increased hair growth. Dr. Lin notes the ongoing seed oil argument and says she is reporting what the studies show.
The pharmacological options come with real effect sizes and real trade-offs. Finasteride is FDA-approved for male pattern hair loss and reduces DHT by around 60%; dutasteride is not approved for this indication but is used off-label at greater potency, cutting DHT by over 90%. Both are avoided in women of childbearing age given birth defect risk, and both carry reported side effects including decreased libido, erectile dysfunction and rarely depression — what some people call post-finasteride syndrome, which Dr. Lin says she has scarcely if ever seen in her own patients but raises anyway. For women, spironolactone blocks androgen receptors, with dizziness, fatigue and menstrual irregularity among its effects; she is reluctant to reach for it unless loss is severe, given growing appreciation of testosterone's benefits in women.
The cellular tier ranges from available to speculative and she labels which is which. Low-level light therapy improves mitochondrial function and fibroblast collagen synthesis, and has been studied alongside actives including arginine and biotinoyl tripeptide-1, raising VEGF and β-catenin. PRP concentrates the patient's own platelets and growth factors — PDGF, EGF, VEGF — with density improvements after a few sessions, though efficacy varies by preparation method. NMN reduces oxidative stress in dermal papilla cells while suppressing androgen receptor and DKK1 expression. Annurca apple polyphenols promote keratin production. Mesenchymal stem cell approaches remain research-stage. The hard constraint underneath all of it: transplantation exists because once follicles are gone there is nothing left to rejuvenate, which is the case for acting early.

Chapters

05:00

Cellular Energy and Hair Health

Questions

Why is my hair thinning in my 30s?

Dr. Lin's clinical example is exactly this scenario — a patient in her late thirties with sudden thinning, where the workup found perimenopause alongside nutritional deficiencies. Both her hair and her energy and mood recovered once those were addressed. Hair follicles are among the most metabolically active structures in the body, so they show strain early when something systemic is off. The usual culprits worth ruling out are iron deficiency, which is one of the most common causes in menstruating women, thyroid and hormonal shifts including falling estrogen, vitamin D status, and periods of significant stress — which pushes follicles out of the growth phase, with the visible thinning arriving months later.

Does biotin actually help hair growth?

It is genuinely necessary — biotin is essential for producing keratin, the main structural protein in hair, and even mild deficiency can cause brittle or thinning hair. But Dr. Lin is clear that more is not better, and taking large amounts if you are not deficient does not produce better hair. The more actionable point is one most people are never told: biotin interferes with a wide range of laboratory assays. If you have blood work scheduled, pause biotin supplements at least three days beforehand and possibly up to a week, or the results can be distorted enough to confuse both you and your doctor.

What is DHT and how does it cause hair loss?

DHT is a potent androgen produced from testosterone by the enzyme 5-alpha-reductase, and it damages follicles through several mechanisms at once. It binds androgen receptors on dermal papilla cells and causes follicular miniaturisation — follicles shrink and produce progressively thinner, shorter, more fragile hairs. It arrests the cell cycle so the growth phase shortens. It downregulates the Wnt/β-catenin pathway that follicle growth depends on, and activates TGF-β/SMAD signalling that accelerates shrinkage. Where you lose hair follows androgen receptor density: temples and crown have more of them, the back of the head fewer — which is why that region stays fuller and is used as the donor site in transplants.

Finasteride vs dutasteride — what's the difference?

Both are 5-alpha-reductase inhibitors that reduce conversion of testosterone to DHT, but they differ in potency and regulatory status. Finasteride is FDA-approved for male pattern hair loss and lowers DHT by roughly 60%. Dutasteride is not approved for this indication and is used off-label, but is more potent — reducing DHT by over 90% — and is generally considered more effective. Both are typically prescribed to men, and women of childbearing age should avoid them because of birth defect risk. Reported side effects include decreased libido, erectile dysfunction, and rarely depression, sometimes described as post-finasteride syndrome; Dr. Lin notes she has seen little to none of this in her own patients but raises it so people can weigh it.

Do hair supplements like Viviscal or Nutrafol work?

Dr. Lin's answer is a lesson in how to read the evidence rather than a yes or no. Viviscal is built on a marine protein complex called AminoMar C, with studies reporting increased volume and reduced shedding after consistent use. Nutrafol uses saw palmetto and ashwagandha to target hormonal and stress contributors. Pantogar, from Germany, combines amino acids, keratin and B vitamins. Her caveat is that studies on commercialised supplements are typically funded by the companies selling them, which is a real reason for discount — but not a reason to dismiss them outright. What she looks for is whether the study is well conducted, whether it replicates in independent labs, and whether the effect is clinically significant rather than merely statistically so.

Can grey hair be reversed?

Dr. Lin frames greying and thinning as the same underlying process rather than separate problems, which is the useful part of the answer. Grey appears when melanocytes — the cells she describes as tiny artists painting each strand — lose the ability to produce pigment, and they are particularly susceptible to oxidative stress from UV exposure, pollution and ordinary metabolism. That means the interventions aimed at thinning are largely the same ones relevant to pigment: reducing oxidative stress through antioxidants from berries, green tea, dark chocolate at 70% cocoa or higher, spinach and kale, and supporting mitochondrial function. She stops short of promising reversal, presenting this as slowing a process driven by oxidative damage rather than undoing it.

The Longevity Letter