The study, which shows that even modest levels of iron deficiency have a negative impact on cognitive functioning in young women has strong implications as iron deficiency still affects around 10 per cent of young women in developed countries.
While iron is known to play a role in cognition, as well as a number of other areas such as immune response and temperature regulation, deficiency was once presumed to exert most of its deleterious effects only if it had reached the level of anaemia.
The new study adds to growing recognition that many organs show negative changes in functioning before there is any drop in iron haemoglobin concentration.
It is also thought to be the first evidence to show that taking iron supplements can reverse the impact on cognition in this age group.
Researchers at Pennsylvania State University carried out a baseline cognition test and a number of other tests, looking at memory, stimulus encoding and retrieval, on 149 women aged 18 to 35. The subjects were classified as iron sufficient, iron deficient but not anaemic, or anaemic.
The women were then given either 60 mg of iron (elemental iron) or placebo daily for four months. At the end of that period, the 113 women remaining in the study took the same task again.
On the baseline test, women who were iron deficient but not anaemic completed the tasks in the same amount of time as iron sufficient women of the same age, but they performed significantly worse.
Women who were anaemic also performed significantly worse, but in addition they took longer.
The more anaemic a woman was, the longer it took her to complete the tasks. However, supplementation and the subsequent increase in iron stores markedly improved cognition scores (memory, attention, and learning tasks) and time to complete the task, said the researchers, presenting their findings at the Experimental Biology meeting in Washington earlier this week.
Iron deficiency is the UK's most common nutritional disorder. Researcher Laura Murray-Kolb said iron deficiency remains at 9 - 11 per cent for women of reproductive age and 25 per cent for pregnant women. In non-industrialized countries, the prevalence of anaemia is over 40 per cent in non-pregnant women and over 50 per cent for pregnant women and for children aged five to 14.