Does multiple micronutrient fortification improve health?
Background
Vitamins and minerals are important for growth and body functioning. Micronutrient deficiencies are common in many populations, and food fortification is one of the interventions to reduce the burden of micronutrient deficiencies and improve health in the general population. Food fortification involves adding micronutrients to processed foods. There have been studies with various single micronutrient fortification, dual micronutrient fortification and multiple micronutrient fortification, including zinc, iron, selenium, vitamin A, vitamin B complexes, vitamin C and vitamin E. The review authors reviewed the evidence about the impact of food fortification with multiple micronutrients (MMNs) on health in the general population.
Study characteristics
The review authors included 43 studies (48 papers) in 19,585 participants (17,878 children) in this review. The evidence is current to August 2018. Most of the included studies assessed the impact of food fortification with MMN compared to placebo or to no intervention; two studies compared food fortification with MMN to iodised salt and one study compared food fortification with MMN to food fortification with calcium alone. Most of the studies (36 out of 43) targeted children. Twenty studies were conducted in developing countries. Food used for fortification included staple foods, such as rice and flour; dairy products, including milk and yogurt; non‐dairy beverages; biscuits; spreads; and salt. A high proportion of studies were funded by commercial sources (e.g. manufacturers of micronutrients), which can be associated with finding more beneficial effects than independently‐funded studies.
Key results
Food fortification with MMN may reduce anaemia by 32%, iron deficiency anaemia by 72%, micronutrient deficiencies (including iron deficiency by 56%, vitamin A deficiency by 58%, vitamin B2 deficiency by 64%, vitamin B6 deficiency by 91% and vitamin B12 deficiency by 58%). MMN fortification may also improve child growth measured as weight for age and weight for height/length. The review authors were uncertain of the effect of MMN fortification on zinc deficiency and child growth measured as height/length for age. The included studies did not report on any side effects associated with MMN fortification, including deaths and diseases. The review authors were uncertain of the effect of food fortification with MMN compared to iodised salt for iron deficiency anaemia and vitamin A deficiency.
Implications for practice
The evidence from this review suggests that MMN fortification when compared to placebo may improve anaemia, iron deficiency anaemia, micronutrient deficiencies (including iron, vitamin A, vitamin B2 and vitamin B6 deficiency), serum haemoglobin, serum folate, serum ferritin, serum vitamin A, serum vitamin B12 and some motor and cognitive outcomes. However, there are a number of other factors that should also be considered. Firstly, the quality of the evidence was low to very low. Secondly, there are no reported data to assess possible side effects of the MMN fortification. Thirdly, the review authors could not draw reliable conclusions from various subgroup analyses on population groups, food vehicles, dosage and region, due to a limited number of studies in each subgroup and measuring varying outcomes. Lastly, the review authors remain cautious about the level of commercial funding among the included studies, although a direct effect of commercial funding was not demonstrated in this review.
Implications for research
The findings of the review provide a number of implications for future research. Future research should focus on generating high‐quality evidence with longer follow‐ups, and assessing the impact in various population groups. The evidence can be consolidated with the use of larger sample sizes and better study designs. It would also be important for study authors to report allocation, randomisation and blinding procedures in detail. There is a need for non‐commercially funded studies and independent evaluations. There are limited data on how fortification affects population groups with variable baseline health status and underlying micronutrient deficiencies and levels of malnutrition. Research should also focus on evaluating the direct health outcomes, including morbidities, mortality and adverse events, especially in LMIC settings. It is also important to report on equity variables for future studies, to assess whether food fortification has any impact on equity.
Read the full review here