Fifty percent of men will have significant hair loss by age 50. The mechanism is well understood. The supplement industry's response to it is mostly not.
Hair loss is one of the most searched health topics on the internet and one of the most commercially exploited. The gap between what the science says and what the supplement industry claims is unusually wide here — which makes it worth examining carefully.
Most hair loss falls into one of two categories. Androgenetic alopecia (AGA) — pattern hair loss — accounts for the majority of consultations in hair referral centres and affects at least 50% of men by age 50 and up to 40% of postmenopausal women. Telogen effluvium (TE) is a diffuse shedding triggered by systemic stress — illness, surgery, rapid weight loss, childbirth, severe psychological stress — and is typically temporary.
Androgenetic alopecia is driven by dihydrotestosterone (DHT), a metabolite of testosterone produced by the enzyme 5-alpha reductase. In genetically susceptible follicles — primarily those on the crown and temples — DHT binds to androgen receptors and triggers a process called follicular miniaturisation. The follicle progressively shrinks over successive hair cycles: the anagen (growth) phase shortens, the telogen (resting) phase lengthens, and the hair shaft produced becomes finer and shorter until the follicle eventually stops producing visible hair altogether.
The genetic susceptibility is polygenic and incompletely understood, but the androgen receptor gene on the X chromosome is a major contributor — which is why the maternal grandfather's hair is a better predictor of male pattern baldness than the paternal grandfather's. The mechanism is well established; the only clinically proven pharmacological interventions act on it directly: finasteride (a 5-alpha reductase inhibitor) and minoxidil (which extends the anagen phase through a different mechanism).
Telogen effluvium is a different problem. A normal scalp maintains roughly 85–90% of hairs in the anagen phase at any given time, with about 100 hairs shed daily. A significant systemic stressor — typically occurring 2–3 months before the shedding becomes noticeable — can push a large cohort of follicles into telogen simultaneously. The result is diffuse shedding that can be alarming but is usually self-limiting. Once the triggering stressor resolves, most follicles return to anagen within 3–6 months.
The most common triggers are iron deficiency, thyroid dysfunction, rapid caloric restriction, and post-partum hormonal changes. In these cases, addressing the underlying cause is the treatment. Supplementing iron in an iron-deficient person with TE is effective. Supplementing iron in a non-deficient person with AGA is not.
This distinction — between correcting a deficiency and supplementing in a non-deficient person — is the most important concept for evaluating the hair supplement market.
The paradox of excess
Both zinc and selenium can cause hair loss when taken in excess. This is not a theoretical concern — it is documented in case reports of supplement-induced alopecia. If you are supplementing for hair health, testing serum levels before and during supplementation is not optional; it is the responsible approach.
AGA is a genetic condition driven by DHT. No supplement has been shown to meaningfully slow it. Finasteride and minoxidil work; the evidence for everything else is thin. TE is usually temporary and usually resolves when the trigger is removed. Iron deficiency is the most common correctable cause and the most evidence-supported supplement target. If you are losing hair and want to do something useful, get a blood panel (ferritin, zinc, TSH, full blood count) before spending money on supplements.
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