Anaemia: How does iron deficiency lead to hair loss?

Anemia is defined by an abnormally low level of haemoglobin measured in a blood sample. Haemoglobin is a substance found in the red blood cells of the blood, enabling the transportation of oxygen to all the organs of the body. The most common cause is iron deficiency. A anaemia is defined by the World Health Organisation as a serum haemoglobin level below 12 g/dL.

The initial symptoms of iron deficiency are fatigue and a reduced tolerance to exertion. More severe symptoms can occur, such as skin and conjunctival pallor, tachycardia, and low blood pressure. It is important to note that patients with an iron deficiency can be completely asymptomatic.

Hair loss is a daily occurrence but is entirely normal. Indeed, the head contains around 1 million hair follicles, capable of producing up to 150,000 hairs depending on the individual. Originating from a hair follicle, the life of a hair alternates through different phases:

• The Anagen Phase (2 - 6 years): This is the hair growth phase during which there is a proliferation of matrix cells that form the inner sheath of the root, the cortex, and the medulla of the hair shaft. The synthesis and pigmentation of the hair shaft only occur during this phase. Its duration determines the length of the hair, generally 1 cm per month.

• The catagen phase (2 - 3 weeks): The first sign of the catagen phase is the cessation of melanin production, the pigment responsible for the colour of our hair, in the hair bulb. The hair stops growing but remains attached to its hair follicle.

• The telogen phase (2 - 3 months): After the catagen phase, the follicles rest in a dormant phase, the telogen phase. The hair shaft eventually detaches from its follicle, which is already starting to produce a new hair beneath the skin.

Thus, within a head of hair, not all hairs are necessarily in the same phase as they each have their own life cycle. Some may be in a growth phase, while others are about to fall out. This is why we lose approximately 50 to 100 hairs per day. This hair loss is normal and does not affect the appearance and density of the hair. The number of hair renewal cycles during an individual's lifetime ranges between 12 and 30. However, their life cycles are influenced by hormonal or nutritional variations.

The mechanism by which iron deficiency affects hair loss is not known. All that is known is that iron is a cofactor of the ribonucleotide reductase, an enzyme that limits the speed of DNA synthesis. The cells of the hair follicle matrix are among the cells that divide the fastest in the body and can be extremely sensitive even to a minor decrease in iron availability, thus leading to a decrease in hair growth in the presence of iron deficiency.

A clinical study demonstrated that out of 96 women aged between 3 and 75 years experiencing hair loss, 18 of them (18.8%) had an iron deficiency. These 18 patients were then given iron supplements to take three times a day and were monitored over a period of 2 months to 2 years. For these 18 patients, when their serum iron levels returned to normal, hair loss ceased and regrowth was observed.

These observations suggest that an iron deficiency can lead to hair loss. However, further studies need to be conducted to elucidate its mode of action and to be able to assert that this iron deficiency is responsible for hair loss.

TROST L. B. & al. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. Journal of the American Academy of Dermatology (2006).

OLSEN E. A. & al. Iron deficiency in female pattern hair loss, chronic telogen effluvium, and control groups. Journal of the American Academy of Dermatology (2010).