John: Hello, I'm John Hilton, editor of the Cochrane Editorial unit. In April 2016, Sant-Rayn Pasricha from the MRC Weatherall Institute of Molecular Medicine at the University of Oxford in the UK and colleagues from Australia and Canada published their new review on the use of iron supplementation by menstruating women, strengthening the collection of Cochrane evidence on the treatment of iron deficiency. He describes the latest findings in this evidence pod.

Sant-Rayn: Iron deficiency is a common condition, especially among women losing blood from menstruation. Low levels of iron can eventually cause anaemia and the World Health Organisation recently estimated that 29% of women are anaemic worldwide. While iron deficiency is seen most commonly in low-income countries, iron deficiency and anaemia are common in women in all contexts, affecting health and wellbeing. Iron supplementation is a key treatment and preventative approach for iron deficiency but as well as improving health, it can cause side effects. It’s important, therefore, for people to have access to reliable evidence on both the benefits and adverse effects of iron, taken orally daily, for improving health in non-pregnant women of reproductive age, and that’s what we’ve attempted with our Cochrane Review.
We looked at outcomes that ranged from blood parameters, such as haemoglobin and ferritin concentration, through to side effects, and effects on cognition, fatigue and mood. We screened over 31,000 articles in our search for randomised trials comparing iron with control and found 67 trials, which had recruited eight and half thousand women. We weren’t able to use all the trials for all the outcomes. Most reported on blood parameters but relatively few reported on functional health outcomes and, unfortunately, only a few studies were at overall low risk of bias.
Looking first to the benefits, when a course of iron supplementation had finished, those women who’d received iron were 61% less likely to be anaemic than those in the control group, and on average they had a 5.4 g/L higher haemoglobin concentration. Women receiving iron had a 38% lower risk of iron deficiency, and an increased ferritin concentration. Surprisingly, though only one of the trials specifically reported on the effects of iron on iron deficiency anaemia.
We found that iron supplementation improved exercise performance and that it might reduce symptomatic fatigue among iron deficient women.
Things were less clear for the potential benefits of iron on cognitive performance because the studies could not be combined and individual studies reported conflicting results.
On the harms side, women receiving iron experienced an almost doubling in the risk of gastrointestinal side effects, with specific evidence for increases in loose stools and diarrhea, hard stools and constipation, and abdominal pain.
In summary, daily iron supplementation in women improves iron stores and reduces anaemia. It also has benefits on exercise performance and symptomatic fatigue, but these benefits come with an increased risk of gastrointestinal side effects. Looking to the future, studies need to move their focus from merely measuring blood parameters to evaluating critical functional health outcomes that have been under-studied to date, including iron deficiency anaemia, cognitive performance, wellbeing and mood.

John: If you’d like to look in more detail at the current findings, go to Cochrane Library dot com and search ‘daily iron supplementation for anaemia’. That’s also the place to find future updates of the review should the new evidence become available.