Hair Loss & Nutrition: The Evidence-Based Guide

Hair follicles are among the most metabolically active structures in the human body. Each follicle cycles through phases of active growth (anagen), regression (catagen), and rest (telogen), and this cycle is exquisitely sensitive to nutritional status, hormonal signals, and physiological stress. When the body is under nutritional or metabolic strain, hair is one of the first non-essential structures to be deprioritised — nutrients are redirected to vital organs, and follicles prematurely enter the resting phase. The result, typically appearing two to three months after the triggering event, is telogen effluvium: diffuse, often alarming hair shedding.

Iron: The Most Common Nutritional Cause. Iron deficiency — even without frank anaemia — is the most common nutritional cause of hair loss in women of reproductive age. The key measure is not haemoglobin but serum ferritin, the storage form of iron. Multiple studies have found that ferritin levels below 30 ng/mL are associated with diffuse hair shedding, even when haemoglobin is normal. A 2006 review in the Journal of the American Academy of Dermatology (Trost et al.) concluded that iron deficiency should be considered in all cases of diffuse hair loss in women. Correcting iron deficiency through diet and supplementation typically results in reduced shedding over three to six months. Best food sources: red meat, liver, lentils, spinach, pumpkin seeds, and fortified cereals. Vitamin C consumed alongside plant-based iron sources significantly improves absorption.

Protein: The Building Block of Hair. Hair is composed almost entirely of keratin, a structural protein. Inadequate dietary protein directly reduces hair growth rate and increases shedding. Protein deficiency is a well-established cause of hair loss in conditions such as kwashiorkor, but subclinical protein insufficiency — common in people following very low-calorie diets, restrictive plant-based diets without careful planning, or older adults with reduced appetite — can also contribute to hair thinning. The recommended dietary allowance for protein is 0.8g per kilogram of body weight, but many nutrition researchers argue this is a minimum rather than an optimal intake, particularly for those with active hair loss. Prioritising high-quality protein sources at each meal — eggs, fish, poultry, legumes, Greek yogurt — is a foundational intervention.

Biotin: The Overhyped Supplement. Biotin (vitamin B7) is heavily marketed for hair growth, and the marketing is largely ahead of the evidence. Biotin is important for keratin infrastructure, and biotin deficiency does cause hair loss — but true biotin deficiency is rare in people eating a varied diet. A 2017 review in Skin Appendage Disorders found that all published cases of biotin supplementation improving hair loss involved confirmed biotin deficiency. In people with normal biotin status, supplementation has not been shown to improve hair growth. An important practical note: high-dose biotin supplementation (above 5mg/day) can interfere with thyroid function tests and troponin assays, potentially causing false results. If you are taking biotin supplements, inform your doctor before blood tests.

Stress and Telogen Effluvium. Psychological and physiological stress is one of the most common triggers of diffuse hair shedding. Elevated cortisol disrupts the hair growth cycle by pushing follicles prematurely into the telogen (resting) phase. The shedding typically begins two to three months after the stressor — which is why people often cannot identify the cause, as the triggering event has long passed by the time the hair loss becomes noticeable. Common triggers include major illness, surgery, significant weight loss, childbirth, bereavement, and prolonged psychological stress. The condition is usually self-limiting once the stressor resolves, but addressing the underlying cause — whether nutritional, hormonal, or psychological — is essential for recovery.

When to Investigate Further. Diffuse hair loss that does not respond to nutritional correction warrants further investigation. Key tests to discuss with your doctor include: serum ferritin, full blood count, thyroid function (TSH, free T4), vitamin D, zinc, and in women, hormonal panel including androgens and DHEAS. Androgenetic alopecia (pattern hair loss) has a strong genetic component and responds to different interventions than nutritional deficiency — minoxidil and finasteride have the strongest evidence base for this type. Alopecia areata is an autoimmune condition requiring specialist assessment. Accurate diagnosis is the prerequisite for effective treatment.