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Nearly 40 per cent of girls and young women in the US have insufficient levels of iron in their blood, which can lead to symptoms such as fatigue, brain fog and hair loss. Of these, 16 per cent also have iron deficiency anaemia, a potentially serious condition in which a lack of iron leads to a reduction in red blood cells, which transport oxygen around the body.

Researchers have previously measured rates of iron deficiency and anaemia in high-risk populations, . Studies looking into their prevalence in the US have also explored these conditions at .

To better understand their prevalence on a national scale, at the University of Michigan and her colleagues analysed blood samples and demographic data from 3490 girls and women, aged 12 to 21, who took part in US-wide surveys between 2003 and 2020. No transgender people were included in the study.

They found that 39 per cent of the participants had iron deficiency, which they defined as having levels of ferritin – an iron-carrying protein – at less than 25 micrograms per litre. Of these, 16 per cent had anaemia, defined as haemoglobin levels below 120,000 micrograms per litre.

This is probably largely due to their diets, says Weyand. “There’s been nutrition studies that show that as a whole in the United States, the iron content of the food we eat has decreased over time,” she says. “People are eating less red meat and more are becoming vegan or vegetarian.”

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Supplements can increase a person’s iron levels, but insufficient screening means many don’t know they need them, says Weyand. In the US, the Centers for Disease Control and Prevention , but most aren’t, says Weyand.

People with heavy periods may not seek medical care for their symptoms and many doctors may not ask about them, she says.

Left untreated, , as well as heart and lung-related complications. Iron deficiency can also cause complications before and after birth, says Weyand, although none of the study’s participants were pregnant.

Female iron deficiency and anaemia extend well beyond the US, particularly in low-income countries where malnutrition can be high and access to healthcare is often poor, says at the University of Melbourne in Australia. These areas should therefore be a particularly high priority for screening and treatment, says Pasricha. Poverty raises the risk of iron deficiency, partly because red meat and other iron rich foods can be expensive, says Weyand.

But at Purdue University, Indiana, says that the cut-off the researchers used to define iron deficiency is higher than . The higher the cut-off, the more prevalent the condition will seem, she says.