In this article
Hair needs protein, iron, zinc and some vitamins to grow. When any of these nutrients is lacking, hair loss can increase. But the relationship works mainly in one direction: correcting a deficiency helps, whereas taking supplements without a deficiency does not make hair grow more and, in some cases, even causes hair loss.
In this article we explain which nutrients have evidence, how to tell whether you are lacking any, and what to put on your plate.
Three ideas to remember.
Fica por baixo do resumo, se existir uma segunda foto.
Why hair feels the effects of diet
The hair follicle is one of the structures in the body that divide fastest. It therefore needs a constant supply of energy, protein and micronutrients.
When resources are scarce, the body gives priority to vital organs. Hair is not essential for survival and is among the first to feel the shortage. The typical result is a telogen effluvium: many hairs enter the resting phase at the same time and fall out 2 to 4 months later. We explain this mechanism in Hair loss: why it happens and what to do.
The situations in which diet matters most are:
- very restrictive diets or rapid weight loss, including with weight-loss medicines or bariatric surgery;
- poorly planned vegetarian or vegan diets;
- heavy periods, pregnancy and breastfeeding, which increase iron needs;
- conditions that reduce absorption, such as coeliac disease.
The nutrients that matter
| Nutrient | What is known | Where to find it |
|---|---|---|
| Protein | Hair is keratin, a protein. A lack of protein causes hair loss and thinner hairs | Fish, meat, eggs, dairy, legumes, tofu |
| Iron | In a meta-analysis of 36 studies with more than 10,000 participants, women with hair loss had lower ferritin, even without anaemia (Treister-Goltzman et al., 2022) | Red meat, shellfish, sardines; legumes and green vegetables (with vitamin C for better absorption) |
| Zinc | Deficiency causes hair loss, but it is uncommon in people who eat a varied diet | Shellfish, meat, pumpkin seeds, legumes |
| Vitamin D | Low levels often appear in people with hair loss, but it has not been shown that supplementing without a deficiency helps | Oily fish, eggs and moderate sun exposure |
| Vitamin B12 and folate | A deficiency affects cell production, including that of the follicle; B12 deserves attention in vegan diets | B12: animal products; folate: green vegetables, legumes |
| Omega 3 | Little direct evidence; it is part of a balanced diet | Sardines, mackerel, salmon, walnuts |
The case of iron
It is the most studied nutrient in female hair loss. The meta-analysis mentioned found ferritin on average 18.5 ng/mL lower in women with hair loss. With the classic deficiency threshold (10 to 15 ng/mL), 21% were iron deficient; with a threshold of 30 to 40 ng/mL, considered more sensitive, it was 59%.
In other words: a ferritin "within the normal range" on a lab report can be low for hair. Interpretation should be medical, and iron replacement is only done after the deficiency is confirmed.
Supplements: when they help and when they harm
The reference review on vitamins, minerals and hair loss concludes that supplementation makes sense when there is a confirmed deficiency. Without a deficiency, there is no evidence of benefit (Almohanna et al., 2019).
When excess causes hair loss
- Vitamin A: high doses, in supplements or in some acne medicines, are a known cause of hair loss.
- Selenium: excess causes hair loss and nail changes.
- Iron: taken without a deficiency, it does not help and can build up in the body.
The case of biotin
It is the best-selling supplement "for hair", but biotin deficiency is rare and the evidence of benefit in people without a deficiency is limited. It also carries a little-known risk: it interferes with several blood tests. It can distort thyroid results, mimicking hyperthyroidism, and even troponin, used to diagnose heart attacks. The US medicines agency (FDA) issued a warning in 2017 (Fan et al., 2019).
If you take biotin, tell your doctor and stop it at least 1 day before any blood test, or up to a week if you take high doses.
The practical rule
Blood tests first, then supplements. Find out what to ask for in Blood tests for hair loss: what to ask for.
A plate that helps your hair
No special diet is needed. A Mediterranean diet, with variety and protein at every main meal, covers the needs of most people.
| Meal | Example |
|---|---|
| Breakfast | Plain yoghurt with oats, walnuts and fruit; or wholemeal bread with egg |
| Lunch | Sardines or mackerel with chickpea and pepper salad; or beef steak with black-eyed beans and broccoli |
| Snack | Fresh cheese with tomato; or a handful of pumpkin seeds |
| Dinner | Vegetable soup, followed by fish or chicken with rice and sautéed spinach; or lentil curry |
Tips that make a difference
- Protein at every main meal, not just at dinner.
- Vitamin C alongside plant-based iron: an orange or pepper with legumes improves absorption.
- Coffee and tea away from main meals, because they reduce iron absorption.
- Vegetarians and vegans: combine legumes, wholegrains, seeds and nuts, and keep an eye on B12.
- During weight loss: keep up protein, even when eating less. See Losing weight without losing hair: protein and nutrients.
When to seek a medical assessment
At Luxmed, the Hair Medicine consultation includes a scalp assessment and, when indicated, targeted blood tests, to understand whether diet is behind the hair loss.
Talk to us
The assessment is a conversation, with no obligation. Tell us what concerns you and our team will reply.
Telephone 214 044 241 · info@luxmed.pt
This article is for information only and does not replace a medical consultation.
Frequently asked questions
Which vitamin is lacking when hair falls out?
The deficiency most often linked to hair loss is iron, especially in women of childbearing age. Vitamin D, B12 and zinc may also be involved, but only blood tests can confirm it.
Does a normal ferritin rule out iron deficiency?
Not always. The usual thresholds (10 to 15 ng/mL) detect severe deficiency; values below 30 to 40 ng/mL may already be associated with hair loss.
How long does hair take to recover after correcting a deficiency?
Shedding usually slows within 2 to 3 months, and visible recovery of volume takes 6 to 12 months, because hair grows about 1 cm a month.
Does biotin make hair grow?
There is a clear benefit only in those with a deficiency, which is rare. And it can distort blood tests.
Does eating gelatine or collagen help hair?
They are sources of protein, but there is no evidence that they help more than other good-quality proteins.
Does a vegan diet cause hair loss?
No, if it is well planned. The points to watch are iron, zinc, B12 and total protein.
Scientific references 5
- Treister-Goltzman Y, Yarza S, Peleg R. Iron deficiency and nonscarring alopecia in women: systematic review and meta-analysis. Skin Appendage Disord. 2022;8(2):83-92. Artigo
- Almohanna HM et al. The role of vitamins and minerals in hair loss: a review. Dermatol Ther (Heidelb). 2019;9(1):51-70. Registo
- Fan J et al. When vitamin supplementation leads to harm: the growing popularity of biotin and its impact on laboratory testing. BC Med J. 2019;61(2):66-71. Artigo
- Soleymani T, Lo Sicco K, Shapiro J. The infatuation with biotin supplementation: is there truth behind its rising popularity? A review of the use of biotin for hair loss. J Drugs Dermatol. 2017;16(5):496-500. PubMed
- DermNet. Telogen effluvium. Artigo
Keep exploring