Lack of iron has long been suspected of contributing to hair loss, but previous experiments did not lead to definite answers because of the insufficient number of subjects studied.
The double-blind, placebo-controlled SU.VI.MAX study, carried out over eight years by researchers at French health and medical institute Inserm, tested the impact of a daily dose of antioxidants on 13000 healthy subjects, including 7886 women, and allowed researchers to provide conclusive evidence that iron deficiency and iron depletion are factors in hair loss.
Data from 3,759 non-menopausal women showed that 48 per cent suffered from iron deficiency or iron depletion. Among post-menopausal women only 23 per cent had lower than normal levels of ferritin because iron loss is often due to menstruation and pregnancy.
Researchers cross-referenced data concerning hair loss and iron reserves, as measured by the amount of ferritin in the blood. They were able to show that non-menopausal women in the 'severe hair loss' category had significantly lower iron reserves than women who did not suffer from excessive hair loss.
They were also able to estimate the risk of severe hair loss caused by variations in the levels of ferritin. For example, a woman with a ferritin level of 70µg/l (the average level) whose ferritin level falls to 40µg/l has a 28 per cent greater risk of severe hair loss.
In a questionnaire devised by L'Oréal researchers and distributed to 5000 women participants in the study, more than half of the respondents declared they were concerned by hair loss, and more than 10 per cent described their hair loss as severe.
Health care professionals note that a certain amount of hair loss is normal and that certain factors that cause hair loss, such as hormonal imbalance, medical side effects and psychological factors, are temporary and reversible.
Iron deficiency is the UK's most common nutritional disorder and can lead to symptoms such as decreased appetite, lethargy, delays in cognitive or motor development and behavioural problems. However researchers also tend to caution against overdose of the mineral as it has been linked to increased risk of chronic disease in high doses.