Anemia: How does iron deficiency lead to hair loss?

Anemia is defined by an abnormally low level of hemoglobin measured in a blood sample. Hemoglobin is a substance found in the red blood cells of the blood, allowing oxygen to be transported to all the organs of the body. The most common cause is iron deficiency. A anemia is defined by the World Health Organization as a serum hemoglobin level less than 12 g/dL.

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

Hair loss is a daily occurrence but is completely normal. Indeed, the head contains about 1 million hair follicles, which can produce 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 growth phase of the hair during which there is proliferation of the 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, typically 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 color 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 under 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 on the verge of falling out. This is why we lose about 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 from 12 to 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 for a period between 2 months and 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 affirm 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).