The most common deficiency in modern society to cause hair loss is iron deficiency anemia. About 2-3 months after a major dip in iron (menstrual losses, accident, surgery, or poor dietary absorption) hair may start to dramatically shed. Other deficiencies leading to hair loss include biotin, other B vitamins, vitamin C (scurvy), folic acid and vitamin D. Fortunately, modern societies almost always have these vitamins in a normal diet.