Hair shedding is often a nutritional signal, but rarely the one people expect.
The most common nutrient-related drivers we see in clinic are low iron stores, inadequate protein intake, and impaired absorption rather than a lack of any single “hair vitamin”. And because the hair cycle runs on a delay, what you notice in the shower today usually reflects something that started happening in your body two to three months ago.
Here is what the evidence supports, what it does not, and how we assess it in functional medicine.
Why hair is sensitive to nutritional status
Hair follicle cells are among the fastest dividing cells in the body. Producing keratin is metabolically expensive, and hair is not essential for survival, so when the body is short on energy, protein, or key cofactors, follicles are one of the first tissues to be deprioritised.
The follicle moves through three phases: an active growth phase lasting years, a brief transitional phase, and a resting phase after which the hair is released. Under normal conditions, roughly 85 to 90 percent of follicles are growing at any one time.
When a physiological stressor occurs, a larger proportion of follicles shift prematurely into the resting phase. They do not shed immediately. They shed around two to three months later, all together, which is why the loss appears sudden and alarming. This pattern is called telogen effluvium, and it is the most common form of diffuse shedding we see.
Common triggers include illness with fever, surgery, childbirth, rapid weight loss from any cause (including medication-assisted weight loss), significant psychological stress, iron deficiency, and thyroid dysfunction.
The nutrients with the strongest evidence
Iron stores
Iron has the most consistent association with hair shedding in women, and ferritin is a significant marker to assess. Ferritin reflects stored iron rather than what is circulating, and it is possible to have a normal haemoglobin and full blood count while iron stores are depleted.
The complication is that standard pathology reference ranges are designed to detect anaemia, not to define what is optimal for hair health. A ferritin result can be flagged as within range, while sitting at the very bottom of it. The threshold at which low ferritin contributes to hair shedding is still debated in the literature, and the evidence is associative rather than proven cause and effect. What is clear is that a single “normal” flag on a report does not close the question.
Iron should never be supplemented without testing first. Some people carry genetic variants that cause iron to accumulate, and unnecessary supplementation carries real risk.
Protein
Hair is composed almost entirely of keratin, a structural protein rich in the sulphur-containing amino acids cysteine and methionine. When protein intake is inadequate, hair growth slows and shedding increases.
This shows up most often in people who have recently reduced their food intake substantially, who are eating a plant-based diet without deliberate protein planning, or who are eating well but skipping protein at breakfast and lunch and loading it all into dinner.
A practical starting point is a palm-sized serve of a protein-rich food at each main meal, spread across the day rather than concentrated in one sitting.
Zinc
Zinc is a cofactor for protein synthesis and cell division, both central to follicle function. Deficiency is associated with hair loss, and it is more common in people with poor absorption, high alcohol intake, or diets low in animal foods.
Zinc supplementation is also a good illustration of why more does not equal better. Sustained high-dose zinc can induce copper deficiency, which itself affects hair pigment and structure.
Vitamin D
Vitamin D receptors are expressed in the hair follicle and are involved in initiating the growth phase. Low vitamin D status is observed more frequently in people with several forms of hair loss, though whether correcting it changes outcomes is less well established in the research.
B12, folate and the absorption question
Both are required for the rapid cell division that hair production depends on. Levels are more often affected by absorption than by intake, particularly in people using acid-suppressing medication long term, certain other medications, people with low stomach acid, and those with coeliac disease.
This is the point most nutrition advice misses. You can eat an excellent diet and still be functionally deficient if digestion and absorption are compromised. If shedding persists despite good intake, gut function is worth investigating.
Where the evidence is weaker than the marketing
Biotin
Biotin dominates the hair supplement market, and the evidence behind it is thin. True biotin deficiency is rare in people eating a varied diet, and in those who are not deficient, supplementation has not been shown to improve hair growth.
There is also a practical problem – High-dose biotin interferes with a range of laboratory immunoassays, including thyroid function tests, and can produce results that look abnormal when thyroid function is fine. If you take a biotin-containing supplement, it is worth pausing it for several days before blood tests and mentioning it to whoever is ordering them.
Selenium and vitamin A
Both are required in small amounts and both cause hair loss in excess. Selenium supports the conversion of thyroid hormone into its active form, but the window between adequate and excessive is narrow. High-dose vitamin A and retinoid derivatives are a recognised cause of shedding. Taking too much of either in the hope of improving hair can actually produce the opposite result.
What nutrition cannot resolve on its own
Nutritional status is one input among several, and treating it in isolation is a common reason people don’t see consistent results.
Thyroid dysfunction affects hair in both directions, with underactivity causing diffuse thinning and overactivity causing shedding. Standard testing frequently stops at TSH, which does not tell the full story. We look at thyroid function more comprehensively when hair is involved.
Androgen activity drives female pattern hair loss, where thinning concentrates across the crown and the part line widens. This often sits alongside PCOS and warrants hormonal assessment rather than nutritional treatment alone.
Perimenopause changes the hormonal environment the follicle sits in, and shedding during this transition is common and frequently dismissed.
Postpartum shedding is a physiological telogen effluvium that typically begins around three to five months after birth. It usually resolves, though it resolves more slowly when iron stores are depleted from pregnancy and blood loss.
Eating for hair, practically
The most useful dietary changes are unglamorous and food-based.
- Include a protein source at breakfast, not only at dinner
- Pair plant sources of iron such as legumes and leafy greens with a source of vitamin C in the same meal, which meaningfully increases absorption
- Move tea and coffee away from meals, since tannins reduce iron uptake
- Soak or sprout legumes and grains where practical, which lowers phytate content and improves mineral availability
- Include oily fish, walnuts, or ground linseed in your diet regularly for essential fatty acids, which support the scalp barrier
- Avoid prolonged aggressive energy restriction, which is one of the most reliable ways to trigger shedding
When to seek assessment
For persistent diffuse shedding, functional testing can clarify whether iron stores, thyroid function, absorption, or hormonal factors are contributing, so that treatment is directed rather than guessed at.
Written by Alyssa Wisniewski, functional medicine naturopath at Wellness Vision, Wallsend. BHSc (Naturopathy), AFMCP, ANTA.
This article is general information and is not individual health advice. If you are experiencing hair loss, speak with a qualified practitioner about your circumstances. Book a free discovery call to discuss whether our approach suits you.