Nutritional Deficiencies and Hair Loss: Iron, Vitamin D, Protein, and More

Why Nutrition Affects Your Hair

The hair growth cycle has three phases:

1. The anagen phase is active growth, and it can last anywhere from two to seven years.
2. The catagen phase is a brief transition period of about two weeks. 
3. The telogen phase is a resting stage lasting roughly three months, after which the hair sheds and a new strand begins to grow.

Hair follicles divide rapidly and require a steady supply of nutrients and energy to keep this cycle running smoothly. When your body is under nutritional stress, it redirects resources toward vital organs and treats hair growth as non-essential. But this might not be noticeable until weeks or months down the line. And this is why the connection between nutritional deficiencies and hair loss isn’t always obvious.

This delayed, diffuse shedding is called telogen effluvium. It happens when a large number of follicles enter the resting phase prematurely, usually in response to a physiological stressor like a nutritional deficiency, rapid weight loss, illness, or surgery. And while telogen effluvium is one of the most common nutritionally related hair loss patterns, it may be reversible once the underlying cause is addressed.

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Iron Deficiency and Hair Loss

Iron deficiency hair loss is one of the most thoroughly studied nutritional causes of shedding. Iron is essential for DNA synthesis in rapidly dividing cells, including the cells that build your hair. When stores run low, follicles are among the first structures to feel it.

Ferritin, the protein your body uses to store iron, is more clinically relevant to hair loss than serum iron alone; levels below 30 ng/mL are often associated with shedding, even in people who aren’t technically anemic. Iron deficiency is the most common nutritional deficiency worldwide, with women of reproductive age having the highest risk due to menstrual blood loss.

Premenopausal women, individuals following plant-based or vegan diets (non-heme iron from plants is absorbed less efficiently than heme iron from animal sources), those with heavy menstrual periods, and individuals who have had bariatric surgery or follow very low-calorie diets are most at risk of hair loss caused by an iron deficiency.

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What May Help

Eating more iron-rich foods, including red meat, lentils, spinach, tofu, and fortified cereals, may help prevent or improve low ferritin levels. Pairing plant sources with vitamin C, like a squeeze of citrus over lentils, may further improve absorption of non-heme iron. 

Most importantly, make sure to get your ferritin tested before supplementing. Excess iron can be harmful, and a licensed healthcare provider can confirm whether supplementation is appropriate for you.

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Signs You May Be Iron-Deficient Beyond Hair Loss

Alongside shedding, signs you may be experiencing an iron deficiency include:

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• Fatigue and low energy
• Pale skin
• Brittle nails
• Shortness of breath during activity
• Cold hands and feet
• Trouble concentrating

If you’re experiencing several of the symptoms above, iron is more likely to be a contributing factor. However, a blood test is the only way to confirm.

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Vitamin D Deficiency and Hair Loss

An estimated 40% of US adults are vitamin D deficient, and many have no idea. In fact, vitamin D and hair loss is an active area of research. Vitamin D receptors are present in hair follicles. And when vitamin D binds to these receptors, it may help kickstart the anagen growth phase.

Some studies have found lower vitamin D levels in individuals with androgenetic alopecia and alopecia areata, and one found that lower levels correlated with earlier onset and greater severity of pattern hair loss. 

However, other research has found that while vitamin D deficiency was common among people with alopecia, levels didn’t reliably predict how severe the hair loss was. In other words, current studies show mixed results.

Either way, risk factors for vitamin D deficiency include limited sun exposure, darker skin tone, older age, obesity, and malabsorption conditions. 

Yet, getting an adequate amount through your diet, such as plenty of fatty fish, egg yolks, fortified milk and juice, and mushrooms, may help. It’s always important to get a blood test before supplementing since vitamin D can accumulate in the body, leading to harmful levels.

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Signs You May Be Vitamin D-Deficient Beyond Hair Loss

Signs you may be deficient in vitamin D include:

• Muscle aches or weakness
• Bone pain
• Fatigue
• Low mood
• Slow wound healing
• Brain fog.

Some individuals with low vitamin D may also have no obvious symptoms at all, which is why getting your levels tested regularly may be valuable (especially if you’re experiencing unexplained weight loss).

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Protein Deficiency and Hair Loss

Your hair is made almost entirely of keratin, a protein. Adequate dietary protein supports the entire process of follicle cell division and hair shaft production. When intake is low, whether from crash dieting, restrictive eating, or simply not eating enough during weight loss, your body shifts into conservation mode. This means it may divert amino acids away from hair growth and toward more critical functions.

Protein and hair loss aren’t often linked together, but an ongoing protein deficiency may lead to telogen effluvium. It may be hard to spot the cause, though, since this shedding usually starts months after the dietary change. 

General guidance suggests adults need about 0.8 g of protein per kilogram of body weight per day. Individuals actively losing weight, exercising regularly, or recovering from illness may need more, often in the range of 1.2 to 1.6 g/kg per day. Examples of protein-rich foods include eggs, chicken, fish, Greek yogurt, legumes, tofu, and protein shakes. Yet, the amount of protein in each food varies, meaning it may take tracking and a few calculations to ensure you meet your daily intake.

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Rapid Weight Loss, GLP-1 Medications, and Hair Shedding

If you’re losing weight on a GLP-1 medication, such as semaglutide or tirzepatide, and you’ve noticed hair thinning, you’re probably not imagining it. Telogen effluvium is a known, temporary side effect of rapid weight loss of any kind. 

It’s important to note, however, that this hair shedding may be related more so to the physiological stress of losing weight quickly and, in some cases, by inadequate protein or micronutrient intake during that duration.

This kind of shedding is typically temporary. And a few practical steps may help, such as prioritizing protein at every meal, considering a multivitamin if your diet has narrowed, and mentioning any persistent hair changes to your prescribing provider. Staying mindful of nutritional support during a weight loss program may also go a long way here.

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Other Nutrients That May Affect Hair Health

Beyond the big three, a handful of other nutrients may also impact your hair health.

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Biotin (Vitamin B7)

Biotin is heavily marketed for hair. But the evidence isn’t as definitive as brands suggest.

Deficiency is rare for individuals eating a varied diet, and supplementation only helps those who are genuinely deficient. High-dose biotin may also interfere with certain lab tests, including thyroid panels. In turn, if you’re having blood tests done, it’s worth mentioning to your provider if you’re taking biotin supplements.

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Zinc

Zinc supports hair tissue growth and repair and keeps the oil glands around your hair follicles working properly. Both zinc deficiency and zinc excess have been linked to hair loss. This means supplementing without an actual, proven deficiency may backfire. 

With that in mind, good whole-food sources of zinc include oysters, beef, pumpkin seeds, chickpeas, and cashews.

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Vitamin B12

B12 supports red blood cell production and DNA synthesis, both of which help deliver oxygen to your follicles. Vegans and vegetarians, older adults, and individuals taking metformin long-term are at higher risk of low B12.

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Selenium

Selenium aids antioxidant defense and thyroid function, both tied to hair growth. Similar to zinc, both deficiency and toxicity may cause shedding. In fact, Brazil nuts are so rich in selenium that one or two a day can cover your needs, which also makes supplements rarely necessary.

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Vitamin A

Vitamin A supports cell growth, including in your hair follicles, but both too little and too much are associated with hair loss. High-dose retinol supplements, in particular, have been linked to shedding, making it important to not exceed the upper limit of 3,000 mcg RAE per day.

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How to Know If a Nutritional Deficiency Is Causing Your Hair Loss

At the end of the day, many deficiencies overlap in their presentation and symptoms, and hair loss has plenty of non-nutritional causes too, including androgenetic alopecia, thyroid disorders, autoimmune conditions, and hormonal changes.

This means the best thing you can do is consult with a licensed provider and undergo the appropriate tests. Ask your provider about serum ferritin, 25-hydroxyvitamin D, a complete blood count (which can flag anemia and B12 or folate issues), zinc, and thyroid function. 

Self-diagnosing and self-supplementing without this information may be ineffective at best and counterproductive at worst (especially since excess iron, vitamin A, selenium, and zinc) may all worsen hair loss. Getting tested gives you the most reliable starting point.

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When Nutritional Support Isn’t Enough: Considering a Hair Growth Treatment Program

For many people, hair loss has more than one cause. A nutritional deficiency may be present alongside pattern hair loss or hormonal changes. In those cases, correcting your diet alone may slow shedding without fully restoring density.

This is where a structured, provider-guided hair treatment program may help. It typically includes a thorough assessment of your hair loss pattern and likely causes, prescription options (if any) that a licensed provider may consider based on your individual needs, and ongoing support along the way. 

A licensed provider can help you identify whether your hair loss is nutritional, structural, or both, and build a plan that addresses all the contributing factors. With Eden, our process starts with a simple and quick online intake. From there, we connect you with a licensed provider who can determine whether treatment is clinically appropriate and discuss available options with you.