Nutrition and Hair Biology
The hair growth cycle
Each hair follicle cycles independently through four phases. Understanding this cycle explains why nutritional interventions take time to produce visible results.
| Phase | Duration | What happens | % of hair at any time |
|---|---|---|---|
| Anagen (growth) | 2–7 years | Active cell division at follicle base; hair shaft grows ~1cm/month | 85–90% |
| Catagen (transition) | 2–3 weeks | Growth stops; follicle shrinks and detaches from blood supply | 1–2% |
| Telogen (rest) | 3–4 months | Hair is dormant; follicle rests before releasing the shaft | 10–15% |
| Exogen (shedding) | 2–5 months | Old hair sheds; new anagen hair begins growing beneath | Overlaps telogen |
Healthy hair growth depends on two things: sufficient anagen duration and adequate nutrient supply to the follicle during active growth. Shortened anagen phases produce thinner, weaker hair. Prolonged telogen phases produce visible thinning.
Normal daily shedding is 50–100 hairs. Shedding above this threshold — or noticeable thinning over weeks — suggests disruption to the growth cycle. The cause is often nutritional rather than genetic, particularly in women.
Nutrient deficiencies and hair loss.
Hair follicles are among the most metabolically active structures in the body. They require a constant supply of amino acids, minerals, and vitamins to sustain rapid cell division during anagen. When supplies are insufficient, the body deprioritises hair — diverting resources to more critical organs.
| Nutrient | Role in hair biology | Deficiency effect |
|---|---|---|
| Iron (ferritin) | Oxygen transport to follicle; supports cell division in hair matrix | Telogen effluvium (diffuse shedding), reduced anagen duration, thinning |
| Biotin (B7) | Co-factor for keratin synthesis; fatty acid metabolism for scalp health | Brittle hair, increased breakage, slow growth |
| Zinc | Supports follicle structure, sebum regulation, immune function at scalp | Hair thinning, alopecia, slow regrowth; zinc deficiency directly shortens anagen phase |
| Vitamin D3 | Regulates hair follicle cycling; stimulates new follicle formation | Telogen effluvium, association with alopecia areata; low D3 linked to prolonged telogen |
| Vitamin A | Sebum production for scalp moisture; cell differentiation in follicle | Dry, brittle hair; both deficiency AND excess cause hair loss |
| Selenium | Antioxidant protection of follicle cells; thyroid hormone metabolism | Weak, discoloured hair; thyroid disruption affects growth cycle |
| Protein / amino acids | Hair shaft is 95% keratin; proline and glycine from collagen support follicle structure | Reduced hair diameter, breakage, slow growth, diffuse thinning |
Collagen and hair structure.
The hair follicle sits within the dermis, surrounded by a collagen-rich extracellular matrix. This matrix provides structural support to the follicle and maintains the blood supply that feeds it. As dermal collagen declines with age, the follicle environment weakens.
Collagen peptides provide the amino acids proline, glycine, and hydroxyproline — which the body uses both for collagen maintenance in the dermis and as building blocks for keratin production. Supplementing with hydrolysed collagen supports the structural environment around the follicle, not just the hair shaft itself.
This is why hair improvements from collagen supplementation are typically visible at 4–6 weeks: the follicle environment strengthens first, producing thicker, more resilient hair during the next anagen cycle.
Why nutrition matters more than products.
Topical hair products coat the shaft. They cannot penetrate the follicle or influence the growth cycle. Shampoos, conditioners, and serums address the surface — smoothing, strengthening, and protecting existing hair. They do not grow new hair or prevent loss caused by nutritional deficiency.
Hair growth is an inside-out process. The follicle receives its nutrients from the bloodstream. If the blood does not carry sufficient iron, zinc, biotin, and amino acids, no topical product can compensate. Addressing hair quality at the root — through nutrition — is the foundation that makes everything else more effective.