Iron is the most common deficiency worldwide and a well-known contributor to hair loss. Iron is required to transport oxygen, DNA synthesis, cellular energy, and numerous biochemical activities. It is thought that iron deficiency could contribute to hair loss via its role as a cofactor of ribonucleotide reductase and enzymes that control DNA synthesis.

In addition to the role of iron in DNA synthesis, several genes identified in the hair follicle are, in some part, regulated by iron availability. Iron also plays a vital role in the production of ATP from food, ATP is the body’s main energy source, and low levels of ATP will result in slow-growing and thinning hair.  Keratin cells have a high energy requirement and are particularly sensitive to reduced ATP production.

Low iron levels impact the liver, which is vital for the uptake of fat-soluble vitamins (A, D, E and K), blood sugar regulation, thyroid hormone conversion (T4-T3) and immune tolerance.

Iron deficiency affects hair growth directly and indirectly in several ways.  Iron is essential for producing hemoglobin, a complex that allows red blood cells to carry oxygenated blood throughout the body. Research indicates that, amongst several factors, hair follicles need a hemoglobin level of at least 130 g/L to receive enough oxygen to keep growing with an adequate number of mature red blood cells in circulation for 110 to 120 days. The requirement will be slightly higher ( more than 140 g/L) if there has been a prolonged history of hair loss (1 year or more).