1. Vitamin D Deficiency 

Vitamin D plays a crucial role in the hair follicle cycle by stimulating the growth phase (anagen). A deficiency can result in hair thinning or conditions like alopecia areata, an autoimmune disorder characterised by patchy hair loss. Research suggests that individuals with low vitamin D levels may experience slower hair regrowth and increased shedding (1). 

Sources: Sunlight exposure, oily fish (e.g., salmon), fortified dairy products, and supplements. 

2. Iron Deficiency 

Iron facilitates oxygen transport to hair follicles via haemoglobin. Insufficient iron levels can disrupt the hair growth cycle, leading to telogen effluvium, a temporary form of hair shedding. Women of reproductive age are particularly susceptible due to menstruation-related blood loss (2). 

Symptoms: Brittle strands, thinning hair, and excessive shedding. 

Sources: Red meat, leafy greens (e.g., spinach), lentils, and iron-fortified cereals. 

3. Biotin (Vitamin B7) Deficiency 

Biotin supports keratin production, a structural protein critical for healthy hair. Though rare, biotin deficiency can lead to brittle hair and scalp irritation. It is especially common in individuals with malabsorption syndromes or those on long-term antibiotic therapy (3). 

Sources: Eggs (cooked), nuts, seeds, sweet potatoes, and biotin supplements. 

4. Vitamin B12 Deficiency 

Vitamin B12 is essential for red blood cell formation and DNA synthesis. A deficiency can impair oxygen delivery to the scalp, slowing hair regrowth and causing diffuse thinning (4). 

Sources: Meat, fish, dairy products, fortified plant-based milk alternatives, and supplements. 

5. Folic Acid (Vitamin B9) Deficiency 

Folic acid supports rapid cell division necessary for producing new hair strands. Low levels may result in slower growth and thinner strands (5). 

Sources: Leafy greens (e.g., kale), citrus fruits, beans, lentils, and fortified grains. 

6. Vitamin C Deficiency 

Vitamin C is an antioxidant that aids in collagen synthesis—a protein that strengthens hair—and enhances iron absorption. A deficiency can lead to weak, brittle strands prone to breakage (6). 

Sources: Citrus fruits (e.g., oranges), strawberries, bell peppers, broccoli. 

7. Vitamin E Deficiency 

Vitamin E protects scalp cells from oxidative stress while promoting blood circulation to nourish follicles. Its deficiency can weaken hair structure over time (7). 

Sources: Almonds, sunflower seeds, avocados, spinach.