Fortification of staple foods with vitamin A for vitamin A deficiency

What is the aim of the review?

We wanted to investigate the effects of fortifying common staple foods with vitamin A, with or without other micronutrients, in populations two years of age and older. Staple foods used in public health fortification programmes have included refined sugar, edible vegetable oils and fats, rice, wheat flour, maize flours and corn meals, condiments and seasonings, and powdered or liquid milk. We searched for all the possible information on this question and found 10 eligible studies.

Key messages

Fortifiying staple foods with vitamin A plus other micronutrients may increase the serum retinol concentrations (an indicator of vitamin A stores in the body) and reduce the risk of subclinical vitamin A deficiency (those without clinical eye signs for risk of blinding undernutrition, detected through a serum/plasma retinol 70 μmol/L or less). However, adding vitamin A alone to the staple foods may have little or no effect on vitamin A status or deficiency.

What was studied in this review?

Vitamin A is an essential nutrient vital for good vision, cell growth, and immunity. Many people in low- and middle-income countries have vitamin A deficiency, especially young children, pregnant women, and women of reproductive age, who may not get enough to eat to cover their increased nutritional demands. Long-term deprivation of vitamin A could lead to visual impairment, blindness, common infections of the upper respiratory tract, diarrhoea, and measles.

There are several strategies to combat the vitamin A deficiency, such as supplementing the diet with vitamin A capsules, adding vitamins and minerals in powder form to energy-containing foods, eating more vitamin A-rich foods, and fortifying staple foods with vitamin A during processing. This review focused on the effects of fortifying staple foods with vitamin A for reducing vitamin A deficiency and improving the health of the general population older than two years of age.

What are the main results of the review?

We found 10 relevant studies (involving 4455 participants) from China, India, the Philippines, Bangladesh, Thailand, and Mexico. Three studies provided one study group with staple foods fortified with vitamin A alone, and another group with the same unfortified staple foods. Five studies compared staple foods fortified with vitamin A plus other vitamins and minerals versus the same unfortified staple food, and two studies compared staple foods fortified with vitamin A plus other vitamins and minerals versus no intervention.

No studies compared staple foods fortified with vitamin A versus no intervention.

Government agencies, private agencies, non-governmental organisations, the private sector, and academic institutions funded the studies. The source of funding does not appear to have distorted the results.

The effect of fortification of staple foods with vitamin A alone on vitamin A stores and on subclinical vitamin A deficiency is uncertain. It is uncertain whether this intervention might reduce clinical vitamin A deficiency (night blindness).

We are moderately confident that fortifying staple foods with vitamin A and other micronutrients may not improve vitamin A status. However, children and adolescents in low- and middle-income populations who eat foods fortified with vitamin A and other micronutrients may have a lower risk of subclinical vitamin A deficiency compared to those receiving unfortified staple foods.

We do not know how vitamin A fortification affects other health indicators, such as the rate of disease in the population, mortality, adverse effects, food intake, birth defects (for pregnant women), or breast milk concentration for lactating women. We considered six of the included studies to be of poor methodological quality.

The review authors searched for published studies up to July 2018.

Authors' conclusions: 

Fortifying staple foods with vitamin A alone may make little or no difference to serum retinol concentrations or the risk of subclinical vitamin A deficiency. In comparison with provision of unfortified foods, provision of staple foods fortified with vitamin A plus other micronutrients may not increase serum retinol concentration but probably reduces the risk of subclinical vitamin A deficiency.

Compared to no intervention, staple foods fortified with vitamin A plus other micronutrients may increase serum retinol concentration, although it is uncertain whether the intervention reduces the risk of subclinical vitamin A deficiency as the certainty of the evidence has been assessed as very low.

It was not possible to estimate the effect of staple food fortification on outcomes such as mortality, morbidity, adverse effects, congenital anomalies, or breast milk vitamin A, as no trials included these outcomes.

The type of funding source for the studies did not appear to distort the results from the analysis.

Read the full abstract...
Background: 

Vitamin A deficiency is a significant public health problem in many low- and middle-income countries, especially affecting young children, women of reproductive age, and pregnant women. Fortification of staple foods with vitamin A has been used to increase vitamin A consumption among these groups.

Objectives: 

To assess the effects of fortifying staple foods with vitamin A for reducing vitamin A deficiency and improving health-related outcomes in the general population older than two years of age.

Search strategy: 

We searched the following international databases with no language or date restrictions: Cochrane Central Register of Controlled Trials (CENTRAL; 2018, Issue 6) in the Cochrane Library; MEDLINE and MEDLINE In Process OVID; Embase OVID; CINAHL Ebsco; Web of Science (ISI) SCI, SSCI, CPCI-exp and CPCI-SSH; BIOSIS (ISI); POPLINE; Bibliomap; TRoPHI; ASSIA (Proquest); IBECS; SCIELO; Global Index Medicus - AFRO and EMRO; LILACS; PAHO; WHOLIS; WPRO; IMSEAR; IndMED; and Native Health Research Database. We also searched clinicaltrials.gov and the International Clinical Trials Registry Platform to identify ongoing and unpublished studies. The date of the last search was 19 July 2018.

Selection criteria: 

We included individually or cluster-randomised controlled trials (RCTs) in this review. The intervention included fortification of staple foods (sugar, edible oils, edible fats, maize flour or corn meal, wheat flour, milk and dairy products, and condiments and seasonings) with vitamin A alone or in combination with other vitamins and minerals. We included the general population older than two years of age (including pregnant and lactating women) from any country.

Data collection and analysis: 

Two authors independently screened and assessed eligibility of studies for inclusion, extracted data from included studies and assessed their risk of bias. We used standard Cochrane methodology to carry out the review.

Main results: 

We included 10 randomised controlled trials involving 4455 participants. All the studies were conducted in low- and upper-middle income countries where vitamin A deficiency was a public health issue. One of the included trials did not contribute data to the outcomes of interest.

Three trials compared provision of staple foods fortified with vitamin A versus unfortified staple food, five trials compared provision of staple foods fortified with vitamin A plus other micronutrients versus unfortified staple foods, and two trials compared provision of staple foods fortified with vitamin A plus other micronutrients versus no intervention. No studies compared staple foods fortified with vitamin A alone versus no intervention.

The duration of interventions ranged from three to nine months. We assessed six studies at high risk of bias overall. Government organisations, non-governmental organisations, the private sector, and academic institutions funded the included studies; funding source does not appear to have distorted the results.

Staple food fortified with vitamin A versus unfortified staple food

We are uncertain whether fortifying staple foods with vitamin A alone makes little or no difference for serum retinol concentration (mean difference (MD) 0.03 μmol/L, 95% CI −0.06 to 0.12; 3 studies, 1829 participants; I² = 90%, very low-certainty evidence). It is uncertain whether vitamin A alone reduces the risk of subclinical vitamin A deficiency (risk ratio (RR) 0.45, 95% CI 0.19 to 1.05; 2 studies; 993 participants; I² = 33%, very low-certainty evidence). The certainty of the evidence was mainly affected by risk of bias, imprecision and inconsistency.

It is uncertain whether vitamin A fortification reduces clinical vitamin A deficiency, defined as night blindness (RR 0.11, 95% CI 0.01 to 1.98; 1 study, 581 participants, very low-certainty evidence). The certainty of the evidence was mainly affected by imprecision, inconsistency, and risk of bias.

Staple foods fortified with vitamin A versus no intervention

No studies provided data for this comparison.

Staple foods fortified with vitamin A plus other micronutrients versus same unfortified staple foods

Fortifying staple foods with vitamin A plus other micronutrients may not increase the serum retinol concentration (MD 0.08 μmol/L, 95% CI -0.06 to 0.22; 4 studies; 1009 participants; I² = 95%, low-certainty evidence). The certainty of the evidence was mainly affected by serious inconsistency and risk of bias.

In comparison to unfortified staple foods, fortification with vitamin A plus other micronutrients probably reduces the risk of subclinical vitamin A deficiency (RR 0.27, 95% CI 0.16 to 0.49; 3 studies; 923 participants; I² = 0%; moderate-certainty evidence). The certainty of the evidence was mainly affected by serious risk of bias.

Staple foods fortified with vitamin A plus other micronutrients versus no intervention

Fortification of staple foods with vitamin A plus other micronutrients may increase serum retinol concentration (MD 0.22 μmol/L, 95% CI 0.15 to 0.30; 2 studies; 318 participants; I² = 0%; low-certainty evidence). When compared to no intervention, it is uncertain whether the intervention reduces the risk of subclinical vitamin A deficiency (RR 0.71, 95% CI 0.52 to 0.98; 2 studies; 318 participants; I² = 0%; very low-certainty evidence) . The certainty of the evidence was affected mainly by serious imprecision and risk of bias.

No trials reported on the outcomes of all-cause morbidity, all-cause mortality, adverse effects, food intake, congenital anomalies (for pregnant women), or breast milk concentration (for lactating women).

Share/Save