Does low ferritin/iron cause diffuse hair shedding in women?

The biological relationship between iron levels and hair health is well-established, particularly in women where systemic iron deficiency is a common driver of diffuse shedding.

Mechanistic basis for hair loss

The hair follicle matrix contains some of the most rapidly proliferating cells in the human body. This high rate of mitotic activity creates a significant metabolic demand for iron, which serves as a critical cofactor for several essential enzymes:

• DNA Synthesis: Iron is required for the function of ribonucleotide reductase (RNR), the rate-limiting enzyme that converts ribonucleotides into deoxyribonucleotides. When iron levels are low, RNR activity declines, leading to replication stress and cell cycle arrest in the matrix keratinocytes.
• Energy Production: Iron is necessary for mitochondrial cytochrome function and oxidative phosphorylation, processes that fuel the energetic demands of the hair growth cycle.
• Premature Shedding: When the matrix cannot sustain rapid division due to iron depletion, the hair follicle prematurely transitions from the anagen (growth) phase to the telogen (resting) phase, resulting in diffuse shedding known as telogen effluvium.

Clinical evidence and associations

Clinical research consistently identifies a strong correlation between low iron stores and non-scarring hair loss in women:

• Ferritin Thresholds: While "normal" laboratory ranges for ferritin can be as low as 10–15 ng/mL, clinical research suggests that optimal hair follicle function often requires ferritin levels above 40–70 ng/mL. Studies show that women with diffuse hair loss frequently have mean ferritin levels significantly lower (by 18 ng/mL or more) than healthy controls.
• Prevalence: In large cross-sectional studies, iron deficiency was found to be the most common nutritional deficiency associated with diffuse alopecia. Supplementation to restore ferritin levels has been shown to successfully stabilize shedding and promote regrowth in deficient individuals.

Bottom line

Low ferritin and iron levels directly impair the rapid division of hair follicle matrix cells by inhibiting DNA-synthesizing enzymes like ribonucleotide reductase. This deficiency is a scientifically supported cause of diffuse hair shedding in women, with clinical evidence suggesting that maintaining ferritin levels above 40–60 ng/mL is necessary to support healthy hair growth.