Hair grows from hair follicles, which are some of the body's most active tissue types. They require a constant supply of nutrients to produce keratin, maintain cell division and keep the hair cycle running. When the diet is deficient, or specific nutrients are missing, it is often first noticed in the hair.

The most important nutrients for the hair

Iron

Iron deficiency is one of the most common nutritional causes of hair loss, particularly in women with heavy periods, vegetarians or those with a low meat intake. Low iron stores (low ferritin) can trigger diffuse hair loss — even if the haemoglobin is still within the normal range. A ferritin value below 30 ng/mL is often associated with hair loss and should be treated.

Zinc

Zinc is involved in the building of keratin and in the regulation of the hair cycle. Deficiency can show up as diffuse hair loss, brittle nail quality and slow wound healing. Zinc is found naturally in meat, shellfish, nuts and wholegrains.

Vitamin D

Vitamin D plays a role in the activation of the hair follicles. Deficiency is widespread in Denmark, especially in winter, and is associated with several forms of hair loss, including telogen effluvium and alopecia areata. A supplement of 20-40 µg daily is often recommended for people with a proven deficiency.

B12 and folate

Both B vitamins are necessary for cell division in the hair follicles. Deficiency is most often seen in vegetarians and vegans (B12) and can cause fatigue, paleness and diffuse hair loss. A blood test quickly reveals the status.

Protein

Hair consists of 80-90 per cent keratin, a protein. Strict calorie restriction or a very low protein intake can trigger hair loss, because the body prioritises vital functions over hair production. It is recommended to consume 0.8-1.2 g of protein per kg of body weight per day.

Omega-3 fatty acids

Omega-3 supports the health of the skin and scalp and can reduce inflammation. Found in oily fish, flaxseed, walnuts and chia seeds.

What about biotin?

Biotin is a B vitamin (B7) that is heavily marketed as a hair growth remedy. With a genuine biotin deficiency — which is rare — supplements can restore hair quality. But in people without a deficiency, the evidence that biotin improves hair or nails is weak. It should not be regarded as a standalone remedy for hair loss.

Rapid weight loss and restrictive diets

Rapid weight loss, fasting or very restrictive diets can trigger telogen effluvium 2-3 months after the weight loss has occurred. The body interprets the sudden calorie restriction as stress and sends the hair follicles into a resting phase. If the hair loss occurs after a diet, it typically subsides again once the diet returns to normal.

Supplements — when does it make sense?

General hair vitamins rarely have a documented effect in people without deficiencies. Supplements should be tailored to the actual need, not taken indiscriminately. Overdosing on certain nutrients (especially selenium and vitamin A) can, paradoxically, worsen hair loss.

The best starting point is a blood test at the doctor, which reveals your specific values. Only then does it make sense to supplement in a targeted way.

Diet first, supplements last

For most people, a varied diet is the best basis for healthy hair growth. Make sure you get enough protein, iron-rich foods (red meat, liver, legumes, dark green vegetables), oily fish and wholegrains. Supplements should be regarded as a supplement, not a replacement, and always taken as needed and preferably in consultation with a healthcare professional.