Deficiencies in nutrients such as vitamins A, E, D, iron, B vitamins and L-lysine may cause thinning eyebrows as well as thinning and weak hair. Fat-soluble vitamins A, E, and D all help to stimulate and support healthy hair growth and are found in spinach, carrots, bell peppers, kale, sunflower seeds, almonds, fish and eggs. Iron deficiency is diagnosed by measuring blood levels of ferritin and may be accompanied by frequent infections, brittle or spoon-shaped nails and decreased exercise ability. Sources of iron include meats, legumes, beans and whole grains. B vitamins are essential for metabolic functions in the body, and help the body cope with stress that can lead to hair loss. B vitamins are found in whole grains, leafy green vegetables, and legumes. L-lysine is an essential amino acid that appears to slow hair loss. Food sources include legumes, meat, fish, eggs, cheese and nuts. Therapeutic supplementation with the above vitamins requires consultation with a naturopathic doctor due to the potential for toxicity.