2. Iron

2.1 Iron’s role

Iron is critical for haemoglobin and oxygen transport, DNA synthesis, and numerous enzymes involved in cellular proliferation.

The hair follicle’s rapidly cycling matrix cells are somewhat sensitive to iron availability.

2.2 Iron deficiency and hair loss

Iron deficiency is common in women of reproductive age and is frequently considered in the work-up of diffuse shedding.

In the literature:

• Some studies suggest that lower ferritin (the primary marker of iron stores) is more common in women with chronic telogen effluvium and possibly female pattern hair loss than in controls.
• Other studies have not found a clear-cut association between ferritin and non-scarring alopecia.
• A consistent, universal “ferritin threshold” below which hair loss occurs has not been firmly established.

In practice, many clinicians take a pragmatic stance:

• If ferritin is frankly low and there are risk factors (heavy periods, restricted diet, pregnancy, gastrointestinal loss), iron deficiency is worth treating for overall health and potential hair benefits.
• If ferritin is borderline or normal and there is no other evidence of iron deficiency, high-dose iron supplementation is unlikely to be helpful and can be harmful.

Essentially:

Untreated iron deficiency can contribute to diffuse shedding and poor hair quality. It is worth excluding and correcting where present. But it is not a universal explanation for all hair loss, and “more iron” is not always better.

3. Zinc: deficiency, excess and nuance

3.1 Zinc’s role

Zinc is involved in DNA and RNA synthesis, cell division, immune function, and enzyme activity in the skin and hair follicles.

Animal studies suggest zinc deficiency can impair hair follicle cycling, and replacement restores growth. In humans, severe zinc deficiency clearly causes hair loss, often alongside dermatitis and immune dysfunction.

3.2 Zinc and hair disorders

Human studies show:

• Some cohorts with alopecia areata or telogen effluvium have lower serum zinc levels compared to controls.
• More recent large population studies show only small differences in zinc levels between those with self-reported hair loss and controls, which are of questionable clinical significance.

Importantly, both zinc deficiency and excess can disrupt hair and overall health. Over-supplementation may interfere with copper absorption, impair immune function, contribute to gastrointestinal upset, and, in extreme cases, be associated with increased hair shedding.

Essentially:

True zinc deficiency is a legitimate target; it can be tested and corrected. However, haphazard high-dose zinc supplementation “because it’s good for hair” is neither evidence-based nor risk-free.

4. Vitamin D: immune modulation and hair

Vitamin D receptors are present in hair follicles and play a role in keratinocyte proliferation and differentiation, as well as immune regulation around the follicle.

Several studies have found that in people with non-scarring alopecias, including alopecia areata, androgenetic alopecia, and telogen effluvium, they are more likely to have low serum vitamin D levels than controls.

What remains less clear is whether low vitamin D contributes causally to hair loss or simply reflects general health, reduced sun exposure, or inflammation.

Correcting a documented vitamin D deficiency is sensible for bone and general health. It may offer modest supportive benefits for hair, particularly in inflammatory alopecias, but it is not a standalone cure.

5. Protein and energy malnutrition

5.1 Crash diets and restrictive eating

Hair follicles require a steady supply of amino acids to build keratin. When calorie or protein intake is suddenly and substantially reduced, as in crash diets, very low-calorie regimens, or severe eating disorders, the body reallocates resources away from nonessential tissues. Hair follicles may synchronously enter telogen, leading to a telogen effluvium several weeks later.

Clinical patterns include:

• diffuse shedding, often noticed when washing or brushing,
• coinciding with weight loss or a significant dietary change,
• generally reversible if adequate nutrition is restored and maintained.

5.2 Chronic under-nutrition

Long-term suboptimal intake, even without significant weight loss, can lead to slower hair growth, thinner hair shafts, and an overall reduction in hair volume.

In these scenarios, hair loss is a barometer of broader under-nutrition and should prompt a review of dietary patterns and, if appropriate, screening for eating disorders.

6. B12, folate and other haematological nutrients

Vitamin B12 and folate deficiencies can cause anaemia, neurological symptoms, glossitis, and, in some cases, diffuse hair thinning.

The mechanism is largely through effects on DNA synthesis and red blood cell production, impacting oxygen delivery and cell proliferation. Hair changes alone are rarely the first or only sign; they sit within a wider picture of ill health.

Corrections of B12 or folate deficiency are important for systemic reasons. Hair may improve once overall metabolic balance is restored, but supplementation in the absence of deficiency has not been shown to enhance hair growth.

7. Essential fatty acids

Essential fatty acids play key roles in cell membrane structure, skin barrier function, and inflammatory signalling.

Severe essential fatty acid deficiency, which is rare in high-income settings, can lead to dry, scaly skin; brittle hair and hair loss; and poor wound healing.

This is typically seen in profound malabsorption, prolonged parenteral nutrition without adequate supplementation, or extreme diets.

For most people eating a varied diet, essential fatty acid deficiency is not a driving factor. General dietary patterns (Mediterranean-style diets, adequate omega-3s) may support global health and reduce inflammation, which, in turn, may indirectly support hair.

8. Biotin and B vitamins: reality versus marketing

Biotin (vitamin B7) is heavily marketed for hair, skin and nails.

What is known

• True biotin deficiency is rare and usually associated with genetic enzyme defects, severe malnutrition, chronic alcohol use or prolonged anticonvulsant therapy.
• In true deficiency, hair loss, rash and nail changes can occur and respond to biotin replacement.
• In otherwise healthy individuals with normal biotin status, clinical trials have not demonstrated a convincing benefit of extra biotin for hair growth.

However, high-dose biotin supplementation is not harmless: it can interfere with numerous laboratory tests, including thyroid and cardiac markers, leading to misdiagnosis or missed diagnoses. It also adds cost and extra pills without clear evidence of benefit for most people.

The same general principle applies to many B vitamins: deficiency should be corrected when identified; oversupplying in replete individuals does not translate into extra hair growth.

9. Selenium, copper and other trace elements

Trace elements are a good illustration that “more” is not always better.

9.1 Selenium

• Both selenium deficiency and excess can impact hair.
• Excessive selenium intake (through supplements or extreme diets high in selenium-rich foods) has been linked with hair shedding and brittleness, often alongside nail changes and systemic symptoms.
• Recommended intakes are relatively low; chronic intakes several times above the recommended amount can be problematic.

9.2 Copper

• Severe copper deficiency, sometimes seen after bariatric surgery or in malabsorption syndromes, can lead to anaemia, neurological issues and brittle hair.
• Excess copper is also toxic. Supplements containing high copper doses without proven deficiency are unnecessary and potentially harmful.

The sensible approach with trace elements is to correct documented imbalance, not to take high doses “just in case”.

10. Medical conditions that create deficiencies

Sometimes the nutritional issue is not what is being eaten, but what the body can absorb or retain.

Conditions that can predispose to deficiencies relevant to hair include:

• coeliac disease,
• inflammatory bowel disease,
• bariatric surgery,
• chronic gastrointestinal bleeding,
• chronic kidney or liver disease,
• restrictive eating disorders.

In these contexts, hair loss is often one of many manifestations. Management focuses on the underlying disease, with targeted nutritional support as part of that.

11. Hair supplements: where they fit, where they do not

The market for “hair vitamins” is large and aggressive. Most formulations contain mixtures of:

• biotin,
• zinc,
• iron,
• vitamin D,
• B vitamins,
• and various botanicals.

Patterns worth noting:

• Many people taking hair supplements are not deficient in the nutrients they contain.
• Some formulations exceed safe upper limits of certain micronutrients.
• Few products have robust, independent evidence demonstrating benefit beyond what would be achieved by correcting specific deficiencies.

A more rational strategy is:

1. Take a careful history (diet, weight change, menstrual loss, GI symptoms).
2. Investigate appropriately (ferritin, B12, folate, vitamin D, zinc, coeliac screening where indicated).
3. Correct what is actually low, with appropriate doses and durations.
4. Reassess hair and general health over several months.

Supplements can be useful as a vehicle to deliver needed nutrients in a palatable way. They are not, by themselves, treatments for androgenetic alopecia or scarring alopecias.

Supplements for hair loss are covered in more detail in their own separate article within Prevention and Hair Health.

12. Practical recommendations

Summarising what is reasonable from a nutritional standpoint:

• Eat a balanced, adequate diet with regular protein intake, plenty of whole foods, and sufficient calories to avoid chronic negative energy balance.
• Avoid crash diets and extreme regimens; make weight-loss attempts gradual and sustainable.
• If you have heavy periods, GI symptoms, or follow a very restrictive diet, discuss iron status and relevant tests with your doctor.
• Do not start handfuls of supplements “for hair” without a clear rationale; more is not always better, and some excesses can cause harm.
• If hair loss is significant or persistent, prioritise a proper medical assessment; nutrition is one piece of the jigsaw, not the whole picture.

13. Core messages

• Hair follicles depend on adequate nutrition, but most common hair loss is not caused purely by what you eat.
• Iron deficiency, severe zinc deficiency, protein–energy malnutrition and certain vitamin deficiencies can contribute to shedding, especially in women.
• Evidence for routine high-dose biotin, zinc, or multivitamin supplementation in well-nourished individuals with hair loss is weak, and such doses can carry risks.
• Excess of some nutrients (vitamin A, selenium, zinc, and iron) can also trigger or worsen hair loss.
• Targeted investigation and correction of genuine deficiencies make more sense than blanket supplementation.
• Nutrition should be viewed as a supportive infrastructure for hair health, working alongside specific treatments directed at the underlying diagnosis.