Hair Structure

Before exploring why hair loss occurs, it helps to understand the basic structure of hair itself. Each strand of hair is more than just what we see on the surface—it is a complex mini-organ nourished by blood vessels, nerves, and surrounding tissue.

• Hair shaft: The visible part above the scalp, made of keratin proteins.

• Hair root: The portion below the skin, housed in a follicle.

• Hair follicle: A dynamic structure embedded in the dermis, containing the dermal papilla (which supplies nutrients and oxygen via blood vessels) and the matrix (rapidly dividing cells that produce the hair shaft).

• Sebaceous gland: Attached to the follicle, secretes oils to lubricate the hair and scalp.

• Arrector pili muscle: A tiny muscle that contracts to make hair stand on end (“goosebumps”).

(Lin, Zhu and He, 2022).

Because the follicle is metabolically active and constantly cycling through growth phases, it has high nutrient and energy demands. Any disruption in supply—whether through illness, stress, or nutritional deficiency—can affect hair growth and quality.

Hair Growth Cycle

Hair strands grow in a cycle with distinct phases:

• Anagen (growth phase): This active growth phase lasts about 2–7 years, and roughly 85–90% of scalp hairs are in anagen at any given time . During anagen, hair continuously grows from the follicle.

• Catagen (transition phase): A short 2–3 week transitional period in which growth stops and the hair follicle shrinks away from its blood supply . Only a small fraction (~5%) of hairs are in catagen at once.

• Telogen (resting phase): A resting phase of about ~3 months (range ~2–4 months) when growth is dormant . Around 10–15% of hairs are in telogen; at the end of this phase, the hair is shed as new growth pushes through. (Some sources consider the shedding as a separate exogen phase.)

Under healthy conditions, lost hairs are replaced by new ones in synchrony. However, disrupting the normal cycle – for example, too many hairs entering telogen or a shortened anagen duration – will result in excessive shedding or visible thinning of hair . In other words, any significant disturbance to the hair growth cycle can create noticeable hair loss and thinning.

Common Types of Hair Loss

Several common forms of hair loss have distinct causes and patterns:

• Androgenetic Alopecia (pattern hair loss): A hereditary, hormone-driven hair loss. In men, it typically presents as a receding hairline and thinning at the crown; in women, it causes more diffuse thinning across the top of the scalp (while the frontal hairline is often preserved). The hormone dihydrotestosterone (DHT) is a key driver that shortens the anagen phase in genetically susceptible hair follicles .

• Telogen Effluvium: A temporary diffuse shedding triggered by a physiological or emotional stressor – for example, severe illness, surgery, childbirth (postpartum hair loss), crash dieting, or nutritional deficiency. Hair shedding usually begins about 2–3 months after the triggering event and can be alarming . Fortunately, telogen effluvium is often self-limiting: once the underlying cause is addressed, excessive shedding tends to cease within about 3–6 months , and hair growth returns to normal.

• Alopecia Areata: An autoimmune condition in which the immune system mistakenly attacks hair follicles. It typically causes patchy bald spots on the scalp or other hair-bearing areas. The hair loss can be sudden, and the affected follicles go into an extended resting phase due to immune attack. Alopecia areata often presents as distinct round or oval patches of loss . (In more severe cases, it can progress to total scalp hair loss or even total body hair loss.)

• Traction Alopecia: Hair loss caused by repeated mechanical trauma to hair follicles, usually from chronic tension or pulling. Tight hairstyles – such as braids, cornrows, tight ponytails, or extensions – can damage follicles over time. Initially this causes breakage and thinning at stress points (often the hairline or wherever hair is pulled tight); if the traction is prolonged, it may lead to permanent follicle damage and scarring in those areas.

When hair loss is not due to genetics or an autoimmune disease, lifestyle and especially nutrient status become important factors. In many cases of diffuse hair shedding, improving one’s nutrition and correcting any deficiencies can help support the return of a normal hair growth cycle.

Nutrient Deficiencies and Hair Loss

Hair follicles are among the most metabolically active cells in the body. They continuously produce keratin (the protein that hair is made of) and cycle through growth phases, so a steady supply of nutrients is critical for healthy hair. Micronutrients – vitamins and minerals – play key roles in the hair follicle’s cellular turnover and immune function. Even relatively mild deficiencies can disturb the hair growth cycle, potentially pushing hairs into telogen (shedding) or shortening the growth phase. Below are some key nutrients linked to hair health:

Iron: Iron is essential for oxygen delivery and DNA synthesis in hair follicle cells. Low iron stores (typically measured by serum ferritin) are strongly associated with diffuse hair shedding, especially in women . In fact, iron deficiency can reduce the proliferation of matrix cells in the hair bulb, which may arrest growth and precipitate telogen effluvium. Studies have found that women with chronic telogen effluvium or pattern hair loss often have significantly lower ferritin levels than those with no hair loss. Sources: Iron-rich foods include lean red meat, poultry, fish, legumes (beans, lentils), spinach, and pumpkin seeds. If iron deficiency is confirmed, supplements can help – but they should be taken under medical guidance, as excess iron can be harmful.

Vitamin D: Vitamin D plays a regulatory role in the hair follicle cycle and is thought to support follicle function. Notably, low vitamin D status has been observed in various hair loss conditions. For example, one case-control study found women with telogen effluvium and female-pattern hair loss had markedly lower vitamin D levels compared to healthy controls . Similarly, patients with alopecia areata tend to have deficient vitamin D levels, and improving vitamin D status may promote regrowth. Vitamin D is believed to help maintain the anagen (growth) phase and modulate immune function in the follicle. Sources: Sunlight exposure enables the body to produce vitamin D; dietary sources include fatty fish (salmon, mackerel, sardines), fortified dairy or plant milks, egg yolks, and mushrooms. In cases of low levels, vitamin D supplementation can be beneficial .

B Vitamins (Biotin, Folate, B12): B-complex vitamins are important for cell growth and energy metabolism, which extends to hair follicles. Biotin (vitamin B7) in particular is often marketed for hair and nail health because it’s involved in keratin production. True biotin deficiency is rare – intestinal bacteria and a balanced diet usually provide enough biotin – but when it does occur, it can cause hair loss, brittle nails, and skin rashes. (One study of women with hair loss found that about 38% had low biotin levels, despite most having no obvious risk factors for deficiency. Routine biotin supplementation, however, is only advised if a deficiency is confirmed .) Folate (vitamin B9) and vitamin B12 are required for DNA synthesis and red blood cell formation. If either is deficient, the resulting anemia or impaired cell division can affect the rapidly-dividing cells in the hair matrix. Some research has noted that deficiencies in biotin, folate, or B12 can be associated with diffuse hair loss . Sources: Biotin is found in foods like eggs (especially yolks), nuts, and whole grains. Folate is abundant in leafy green vegetables, legumes, avocados, and citrus fruits. Vitamin B12 is primarily obtained from animal foods (meat, poultry, fish, eggs, dairy), so vegetarians/vegans may need fortified foods or supplements.

Zinc: Zinc is a trace mineral crucial for protein synthesis, cell division, and immune function. Hair follicles require zinc for building keratin and for normal growth activity. Zinc deficiency can manifest as diffuse hair thinning or, in some cases, patchy loss. Clinical studies have shown that people with hair loss often have lower serum zinc levels than those without. For instance, in one study of different alopecia types, all hair loss patients had significantly lower average zinc levels compared to controls, and zinc deficiency was especially common in those with telogen effluvium and alopecia areata . This suggests inadequate zinc may impair follicle recovery and contribute to shedding. Sources: The best zinc sources include shellfish (oysters in particular are very high in zinc), red meat, poultry, pumpkin seeds, nuts, and legumes. Severe zinc deficiency is uncommon in developed countries, but mild insufficiency can occur with restricted diets or malabsorption issues. If confirmed, zinc supplements can help, though excess zinc should be avoided as it can interfere with other minerals.

Protein: Because hair is made primarily of keratin (a protein), a diet insufficient in protein can impact hair growth. The body will prioritise vital organs and functions over hair production during protein-calorie malnutrition. In extreme cases (e.g. anorexia, famine), diffuse hair loss and hair texture changes are well-documented – children with kwashiorkor or marasmus develop thin, brittle hair that may change color (the “flag sign”) due to protein and micronutrient deficiencies . Even in milder cases – such as crash dieting or very low-protein diets – the hair matrix may not get enough amino acids, leading to increased shedding or slower growth. One review noted that a significant reduction in protein or overall calories (as in some fad diets) can result in telogen effluvium. Sources: Ensure your diet includes adequate protein from sources like lean meats, fish, eggs, dairy, legumes, tofu, or nuts. Generally, adults should consume at least ~0.8 grams of protein per kilogram of body weight daily (more if physically active) to support tissue maintenance, including hair follicles.

Other Nutrients:

• Selenium: This trace mineral supports antioxidant enzymes (like glutathione peroxidase) that protect the hair follicle from oxidative damage. Overt selenium deficiency is quite rare, but has been associated with hair and skin depigmentation and hair loss in extreme cases (observed mostly in areas with selenium-poor soil or in patients on selenium-deficient diets). On the flip side, excess selenium intake can also cause hair loss, so the goal is optimal balance . Most people get sufficient selenium through a normal diet (Brazil nuts, seafood, eggs, and whole grains are good sources).

• Essential Fatty Acids (Omega-3 and Omega-6): Healthy fats are often overlooked, but they are vital for scalp and hair health. Omega-3 fatty acids, in particular, have anti-inflammatory properties and help keep the scalp skin and hair moisturized. A lack of omega-3s can lead to a dry, scaly scalp and brittle hair that loses luster. Some research suggests omega-3 and omega-6 supplementation can improve hair density and reduce shedding. Include sources of omega-3s such as oily fish (salmon, mackerel), flaxseeds or chia seeds, walnuts, and consider fish oil supplements if dietary intake is low.

• Others: Vitamin A and vitamin E are also needed in small amounts for healthy hair growth, but excess of these fat-soluble vitamins can cause hair loss – so supplements should be used cautiously unless a deficiency is identified . Vitamin C is important for iron absorption and collagen formation in the hair shaft. Overall, a variety of vitamins and minerals (magnesium, silica, etc.) contribute to hair’s structure and growth environment, but deficiencies in them are either uncommon or less clearly linked to hair loss.

Supporting Hair Through Nutrition

Given the connections between nutrition and hair, adopting a balanced diet is one of the best strategies to support healthy hair growth:

• Eat a varied, nutrient-rich diet: Emphasize adequate protein intake (to provide amino acids for keratin), along with plenty of colorful fruits and vegetables (for vitamins, minerals, and antioxidants), whole grains, and sources of healthy fats. These provide the broad range of nutrients that hair follicles require. In cases of hair thinning, ensure you’re getting enough iron, zinc, and vitamins D and B – these are common nutrients that, when low, can trigger shedding.

• Correct any deficiencies: If you are experiencing unusual hair loss, consider getting lab tests to check for deficiencies in iron/ferritin, vitamin D, vitamin B12, folate, thyroid levels, and other relevant markers. Treating a confirmed deficiency with supplements or dietary changes can often reverse or slow hair loss related to that deficiency. For example, iron supplementation in iron-deficient individuals or vitamin D supplementation in those deficient can promote regrowth . Always consult a healthcare provider for proper diagnosis and before starting supplements.

• Avoid extreme diets: Rapid weight loss or restrictive fad diets are a common cause of telogen effluvium. Severely cutting calories or entire food groups can deprive hair of essential nutrients and energy. Hair loss often shows up 2–3 months after a crash diet or bout of malnutrition. Aim for slow, steady weight loss (if needed) with balanced nutrition, rather than drastic diets.

• Lifestyle factors: Remember that hair health is not only about diet. Try to manage stress, since significant stress can induce hair shedding by shifting follicles into telogen phase prematurely. Prioritise good sleep and exercise – these improve overall circulation and hormonal balance, which in turn benefit your scalp and hair. Also, be gentle with your hair care: avoid tight hairstyles that pull on roots (to prevent traction alopecia), minimize harsh chemical treatments, and use heat styling tools sparingly. A healthy scalp environment (through mild shampooing, scalp massage, etc.) will support healthy hair growth.

  
  

By understanding the hair growth cycle and the common causes of hair loss, it becomes clear that nutrition forms a crucial piece of the puzzle. While not all hair loss can be solved with diet alone, ensuring your body has all the building blocks it needs will lay the best foundation for resilient, growing hair. In many cases, hair will regrow or thicken once the underlying nutritional or metabolic issues are resolved – but remember that hair recovery takes time. Patience, consistency with healthy habits, and guidance from medical professionals (when needed) are key to restoring hair health.

References:

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• Grover, C. and Khurana, A. (2013) ‘Telogen effluvium’, Indian Journal of Dermatology, Venereology and Leprology, 79(5), pp. 591–603. Available at: https://doi.org/10.4103/0378-6323.116731.

• Gupta, A.K., Wang, T. and Economopoulos, V. (2025) ‘Epidemiological landscape of androgenetic alopecia in the US: An All of Us cross-sectional study’, PLOS ONE, 20(2), p. e0319040. Available at: https://doi.org/10.1371/journal.pone.0319040.

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• Kil, M.S., Kim, C.W. and Kim, S.S. (2013) ‘Analysis of Serum Zinc and Copper Concentrations in Hair Loss’, Annals of Dermatology, 25(4), pp. 405–409. Available at: https://doi.org/10.5021/ad.2013.25.4.405.

• Lin, X., Zhu, L. and He, J. (2022) ‘Morphogenesis, Growth Cycle and Molecular Regulation of Hair Follicles’, Frontiers in Cell and Developmental Biology, 10. Available at: https://doi.org/10.3389/fcell.2022.899095.

• Minta, A. et al. (2023) ‘Editor’s Pick: Diagnostic Evaluation of Hair Loss: A Narrative Review’. Available at: https://www.emjreviews.com/dermatology/article/diagnostic-evaluation-of-hair-loss-a-narrative-review/ (Accessed: 3 October 2025).

• Rasheed, H. et al. (2013) ‘Serum ferritin and vitamin d in female hair loss: do they play a role?’, Skin Pharmacology and Physiology, 26(2), pp. 101–107. Available at: https://doi.org/10.1159/000346698.

• Rushton, D.H. (2002) ‘Nutritional factors and hair loss’, Clinical and Experimental Dermatology, 27(5), pp. 396–404. Available at: https://doi.org/10.1046/j.1365-2230.2002.01076.x.

• Trost, L.B., Bergfeld, W.F. and Calogeras, E. (2006) ‘The diagnosis and treatment of iron deficiency and its potential relationship to hair loss’, Journal of the American Academy of Dermatology, 54(5), pp. 824–844. Available at: https://doi.org/10.1016/j.jaad.2005.11.1104.

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