The randomized, prospective trial, carried out on around 80 South African mothers, was designed to find out whether iron deficiency anaemia in mothers alters their cognition and behaviour and their interaction with their children.
Almost 24 per cent of pregnant mothers in Europe are thought to have anaemia while in the Americas this figure rises to 53 per cent, according to data from the WHO.
The findings could also be significant for mothers without anaemia but lacking in iron intake. Anaemia tends to be less common in richer than in poorer populations but there are frequent cases of iron deficiency among women - it is still the most common of all nutrient deficiencies.
While the new study does not examine the relationship between a deficiency in iron that has not yet caused anaemia and depression, researchers at the same institution - Pennsylvania State University - have recently shown that iron supplements could significantly help concentration and memory in young women, even if they are not anaemic.
Their findings have suggested that many organs show negative changes in functioning before there is any drop in iron haemoglobin concentration, a marker of anaemia.
In the new study, a team from Pennsylvania, the University of Cape Town and the University of North Carolina studied three groups of mothers: non-anaemic controls, anaemic mothers receiving a daily iron supplement (125mg) and anaemic mothers taking a placebo.
Mothers' iron status, socioeconomic, cognitive, and emotional status, mother-infant interaction, and the development of their infants were assessed at 10 weeks after giving birth and nine months later.
Behavioural and cognitive variables at baseline did not differ between anaemic mothers and non-anaemic mothers.
However, iron treatment resulted in a 25 per cent improvement in previously iron-deficient mothers' depression and stress scales, report the researchers in this month's Journal of Nutrition (vol 135, pp267-272).
Anaemic mothers administered placebo did not improve in behavioural measures.
The researchers also found a strong association between iron status variables (hemoglobin, mean corpuscular volume, and transferrin saturation) and cognitive variables (Digit Symbol) as well as behavioural variables such as anxiety, stress, depression.
"There are likely ramifications of this poorer 'functioning' on mother-child interactions and infant development, but the constraints around this relation will have to be defined in larger studies," noted the authors.
A European project is currently examining the safety and efficacy of iron supplementation in pregnant women.