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Does adding iron to wheat flour reduce anaemia and increase iron levels in the general population?
Why is this question important?
Anaemia is a common condition usually caused by low iron levels in the body. Iron is important because it is the main component of haemoglobin, the protein in red blood cells that carries oxygen around the body. If the body cannot produce enough healthy red blood cells to provide the body with sufficient oxygen, people may suffer from problems such as tiredness and inability to concentrate, children may have learning difficulties, and pregnant women and their babies may be at risk of death or developmental problems. People in low‐income countries often have diets that are low in iron, resulting in anaemia or low blood iron levels. Such countries attempt to tackle this problem at the population level by adding iron and other minerals and vitamins (micronutrients) to staple foods, such as wheat flour.
We wanted to know whether adding iron to wheat flour, alone or with additional micronutrients, reduces anaemia and iron deficiency in the general population. We also wanted to know if it causes any unwanted effects, for example diarrhoea, infection or inflammation, constipation, nausea, or death.
How did we identify and assess the evidence?
We searched medical databases for randomised controlled trials (RCTs) that assessed the effects on the general population, aged over two years, of wheat flour with added iron and other micronutrients compared to wheat flour alone or wheat flour with the same added nutrients but no additional iron. RCTs are medical studies where people are chosen at random to receive a treatment (the intervention), or a different treatment or no treatment (the control). RCTs provide the most reliable evidence.
Based on factors such as how studies were conducted and consistency of findings across studies, we categorised the evidence as high, moderate, low or very low certainty. High certainty means we are confident in the evidence, moderate certainty means we are fairly confident, low or very low certainty means that we are unsure or very unsure of the reliability of the evidence.
What did we find?
We found nine relevant RCTs. The study participants were 3166 children, adolescent girls and adult women living in Bangladesh, Brazil, India, Kuwait, the Philippines, Sri Lanka and South Africa. The studies assessed the effects of wheat flour with different forms of iron alone or combined with other micronutrients, compared with wheat flour alone or wheat flour with the same added micronutrients but no iron. Studies lasted from 3 to 24 months and reported anaemia, haemoglobin concentrations, iron deficiency and iron status. Two studies assessed infection and inflammation. None of the included studies assessed diarrhoea, respiratory infections, death, or other unwanted effects. Eight studies clearly reported their source of funding, including three with industry funding.
Wheat flour with iron may have little or no effect on anaemia and probably makes little or no difference in iron deficiency compared to wheat flour alone. We are uncertain whether wheat flour with iron increases haemoglobin concentrations. Wheat flour with iron probably makes little or no difference to individual risk of infection or inflammation.
Wheat flour with iron plus other micronutrients, may make little or no difference to anaemia, probably makes little or no difference to iron deficiency and may or may not improve haemoglobin concentrations compared to wheat flour alone.
We are very uncertain about the effects of wheat flour with iron plus other micronutrients compared to wheat flour with the same micronutrients but no iron on anaemia and iron deficiency, as the certainty of the evidence was very low. Wheat flour with iron may make little or no difference to haemoglobin concentrations.
What this means
We judged the evidence as very low to moderate certainty, which means we are not certain of the effect of wheat flour with added iron on the reduction of anaemia and iron deficiency on people in countries that add iron to wheat flour. We do not know whether adding iron to wheat flour causes unwanted effects because none of the studies reported unwanted effects.
How up to date is this review?
The review is up to date to September 2019.