The global challenge of iron deficiency in the blood and why scientists disagree on whether supplements are the solution

Amanda Ruggeri – BBC

Iron deficiency is the most common micronutrient deficiency in the world today, affecting approximately one in three people. It is especially prevalent in children as well as in women of reproductive age, including pregnant women.

The condition can cause a wide range of consequences. When a pregnant woman lacks iron stores, for example, it can affect the development of the fetus's brain and also has a higher risk of low birth weight, premature birth, and death during pregnancy and childbirth.

For infants and young children, iron deficiency can affect long-term development, with studies finding that children are at risk of exhibiting behavioral problems, are less happy and content, and tend to be more socially withdrawn.

Also, iron deficiency can affect children's motor and cognitive skills even years after a deficiency has been corrected.

In adults, iron deficiency is one of the leading causes of disability in the world. In rare cases, it can be life-threatening.

A widespread problem

“It’s a huge global problem,” says Michael Zimmermann, professor of nutrition at the University of Oxford in Britain and a longtime researcher of micronutrient deficiencies.

"It's very common in all people and doesn't go away easily."

Most scientists agree that iron deficiency is a common condition. But other questions remain, such as how exactly to define iron deficiency, or how likely it is, in the absence of other symptoms, to increase the risk of poor health outcomes. So when should someone supplement their body with iron, and when should they not?

What is not discussed is that some groups are more susceptible to iron deficiency than others.

In women, for example, iron deficiency anaemia, where the body does not have enough iron to produce enough red blood cells, is the leading cause of disability worldwide. A study of first-time blood donors in the US found that iron levels were low in 12% of women, but in less than 3% of men, reflecting the impact of regular blood loss during menstruation. Then there is the impact of pregnancy, which diverts nutrients to the foetus, meaning women in this group are particularly at risk. One study found that 46% of women in the UK had anaemia at some point during pregnancy, although not all cases were due to iron deficiency.

Lifestyle, foods consumed, and frequent blood donation can put everyone at increased risk, both men and women.

People with certain health problems may also be prone to lower iron levels. Kidney disease, for example, can affect iron absorption.

But children are among the most vulnerable groups to iron deficiency, because the mineral is very important for their development.

“What is the fastest period of growth in our entire lifespan? Infancy,” says Mark Corkins, chairman of the Nutrition Committee at the American Academy of Pediatrics (AAP).

We triple our birth weight by the year, as does our height. And as the body grows, it needs more blood, and blood cells are built, in part, on iron.

Without the necessary iron, Corkins says, children risk not being able to produce enough red blood cells to deliver oxygen to growing tissues, including the brain.

"Iron deficiency is particularly common in children from lower-income countries. In studies I have done in Africa, 70% of infants between the ages of 6 and 12 months have clear iron deficiency anemia," says Zimmermann.

Even in wealthier countries, which have better overall nutrition and are more likely to fortify some food products with iron, this deficiency persists. Up to 4% of toddlers in the US, for example, have iron deficiency anemia, while about 15% are iron deficient.

Just because someone has an iron deficiency does not mean they will have anemia.

"Iron deficiency can be considered a pre-anemia stage," says hematologist Sant-Rayn Pasricha, head of the Melbourne School of Global Health, who specializes in iron deficiency and related problems.

A matter of debate

Some specialists question whether iron deficiency is always a cause for concern, especially if it occurs in the absence of any physical symptoms and if the patient does not have anemia.

Pasricha co-authored a review to help inform the World Health Organization's guidelines for iron supplementation in women. In that research, he found something interesting.

While those women in the clinical trials who were iron deficient and reported feeling tired found that their fatigue improved with iron supplementation, the intervention did not change the energy levels of women who were also iron deficient but did not report fatigue.

“This suggests that, at least in adults, if you are clinically unwell with iron deficiency, then of course you should be treated and that will improve the way you feel,” Pasricha says. “But it also suggests that, if you are feeling perfectly well and someone just finds out you have low iron, then it’s hard to be sure that this treatment would make you feel any different.”

According to some studies, the effects of iron deficiency anemia, especially in children, can be long-lasting.

One review, for example, found a “consistent association” between children with iron deficiency anemia having poorer cognitive performance compared to others. However, the researchers point out, it may not be iron deficiency anemia that is the problem. It could be the effect of anemia in general, which lowers energy levels. The researchers also say in their review that it is difficult to rule out the influence of socioeconomic factors on children’s behavior and cognition.

This complexity lies at the heart of all nutrition research: is the lack of a nutrient itself the problem, or is this deficiency a sign of something else going on?

To complicate matters further, the criteria for defining iron deficiency in children are still up for debate, Zimmermann says. Because children are growing so quickly, he adds, iron deficiency normally leads to anemia quickly, which means it's not easy to find and study iron-deficient children who aren't anemic.

To be fulfilled or not to be fulfilled

Given this, and the potential consequences for their development, guidelines often advise that children supplement iron at any sign of deficiency or even supplement as a preventative measure.

In the US, for example, the American Academy of Pediatrics recommends that breastfed babies take iron drops from the age of four months, for example. This is because breast milk has low levels of iron, while formula milk usually has iron.

But some researchers question this approach.

Pasricha was involved in the largest trial to date that has examined the effect of supplements on child development.

The study of 3,300 eight-month-old infants in Bangladesh assigned the children to groups that received either daily iron supplements for three months or a placebo. He and colleagues measured the children's neurodevelopment before and after the supplements.

“We saw no evidence of functional benefit,” he says, although they also saw no harm in any way.

Meanwhile, there may be a downside to supplementing children who don't actually have a deficiency. Several studies have found that infants and toddlers who had adequate iron levels but took supplements had poorer weight gain and less growth compared to controls.

Supplements can have other side effects, too. Zimmermann, for example, has studied how supplementation can affect people's microbiomes.

“These powders have very high amounts of iron in them, which can cause a very rapid shift in the microbiome,” says Zimmermann.

However, many doctors and researchers agree that when someone has iron deficiency or iron deficiency anemia along with symptoms, supplements can be one of the fastest ways to help them get better.

A balanced diet

But in an ideal world, people would get enough iron by eating a balanced diet that includes iron-rich foods and avoid developing a deficiency in the first place, although this is not always possible.

Ingredients such as liver or red meat, legumes, including beans and chickpeas, as well as nuts and dried fruits are all considered good sources of iron.