Nutrient Deficiency

A nutrient deficiency occurs when intake or absorption of a vitamin or mineral is insufficient to meet the body's requirements, resulting in suboptimal biochemical function and eventually clinical symptoms. Deficiencies most commonly associated with hair loss include iron (ferritin <30 ng/mL), vitamin D (<30 ng/mL), zinc, biotin, and vitamin B12. Subclinical deficiencies — levels below optimal but above frank deficiency — may impair hair growth before causing classical deficiency symptoms. Risk factors include restrictive diets, malabsorption disorders, pregnancy, and certain medications. Blood testing (CBC, ferritin, 25-OH-D, zinc, B12) is recommended before supplementation.