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Hair loss and thinning

Hair shedding has a long list of causes, most of which are not nutritional. The commonest by a wide margin is genetic pattern hair loss, followed by telogen effluvium — a delayed shedding response to a stressor two or three months earlier.

General information only, not a diagnosis. A symptom is not proof of a deficiency — most symptoms here have many possible causes, and the common ones are rarely nutritional. Do not start a supplement to treat a symptom; the safe route is a blood test if one is warranted, and a doctor to interpret it. Use the red-flag list on each page, and see a clinician for anything that persists or worries you.

The delay is the single most useful thing to understand here. Hair follicles cycle, and a shock to the system — a serious illness, surgery, a fever, childbirth, a crash diet, severe stress — pushes many follicles into the resting phase at once. They shed together two to three months later, by which time the original cause has been forgotten. People search for a nutritional explanation in the week the hair falls out, when the relevant event was in a different season.

That said, nutrition does appear in the differential. Iron deficiency is associated with hair shedding and is worth measuring, particularly in menstruating women. Very low energy intake — a crash diet, an eating disorder, a period of illness with poor intake — reliably produces shedding, because hair is metabolically expensive and not essential for survival. Severe protein restriction does the same. These are real effects of real deficits, not effects of being slightly below an optimal intake.

Then there is the supplement aisle, which is dominated by biotin. Biotin deficiency does cause hair and nail problems, and it is genuinely rare in people eating a mixed diet. The evidence that biotin helps hair in people who are not deficient is weak. It also carries a specific practical hazard: high-dose biotin interferes with a range of common laboratory immunoassays, including thyroid function tests and cardiac troponin, and can produce results that look like disease or hide it. If you take biotin, tell whoever is ordering your blood tests.

The pattern of loss matters more than any of this. Diffuse thinning across the whole scalp points somewhere different from a receding hairline, and both point somewhere different from discrete round patches or from redness, scaling and scarring. That is a dermatologist question, and it is a question worth asking early, because some causes of scarring hair loss are only treatable before the follicle is lost.

Nutrients commonly discussed for hair loss

Each nutrient below is rated for how strong the evidence is that it relates to this symptom. "Relevant only if you are deficient" means it can matter when your level is genuinely low, but topping it up when it is not low does nothing.

Iron Relevant only if you are deficient

Associated with hair shedding when stores are low, and one of the few blood tests routinely ordered for it. As always, the test comes before the supplement.

Full ranking: foods highest in iron.

Zinc Relevant only if you are deficient

Frank zinc deficiency causes hair loss along with skin changes and impaired healing. It is uncommon in people eating a mixed diet, and zinc supplements taken long-term can interfere with copper absorption, so this is not a nutrient to take speculatively.

Full ranking: foods highest in zinc.

Vitamin D Weak evidence

Frequently measured in hair-loss clinics and frequently found to be low, which is also true of people without hair loss in the same latitude. The causal evidence is not strong.

Full ranking: foods highest in vitamin d.

Biotin Weak evidence

The most marketed and least supported nutrient on this page. Deficiency is rare; supplementation in the absence of deficiency is not well supported; and high doses interfere with common laboratory blood tests, including thyroid and cardiac markers. Tell your doctor if you take it.

Protein Relevant only if you are deficient

Severely inadequate protein or energy intake causes shedding. This is about genuine deficit — crash dieting, illness, disordered eating — not about being slightly under an optimal target. There is no single per-food ranking for protein on this page because it appears on every food page in the reference section.

Source: Foods richest in each nutrient: USDA FoodData Central SR Legacy (public domain), per 100 g · checked 2026-09-02

Causes that are usually more likely

Before a nutrient, these are the explanations a clinician would normally consider first for hair loss:

• Genetic pattern hair loss, in both men and women
• Telogen effluvium two to three months after illness, surgery, fever or childbirth
• Thyroid disease
• Autoimmune conditions such as alopecia areata
• Scalp conditions — fungal infection, psoriasis, scarring alopecias
• Medicines, including some for blood pressure, mood and acne
• Traction from tight hairstyles, and heat or chemical damage
• Rapid weight loss from any cause

When to see a doctor

Treat these as reasons to seek a professional opinion rather than to self-treat:

• Hair loss in discrete round patches
• Redness, scaling, pain or scarring on the scalp
• Sudden loss, or loss of eyebrows, eyelashes or body hair as well
• Hair loss alongside new facial hair, irregular periods or acne
• Hair loss with tiredness, weight change or feeling cold — a thyroid pattern
• Any hair loss that is leaving smooth, shiny, follicle-free skin behind

This list is not exhaustive, and a symptom that is severe, persistent or getting worse always deserves a professional opinion. If you feel very unwell, seek urgent care rather than reading further.

Frequently asked questions

Other symptoms

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