Vitamin A (VA) deficiency affects approximately 40% of the world population, particularly pregnant or lactating women and under-five children 1. An estimated 100–140 million children are still suffering from subclinical VA deficiency, although clinical signs of the deficiency are on the decline 1. Even subclinical VA deficiency is associated with 23% excess mortality of under-five children 2 and with maternal mortality 3. Sahelian countries, including Burkina Faso, are the most affected by VA deficiency in sub-Saharan Africa. In a small community-based study conducted in 1999 in the north-central part of Burkina Faso, 84.5% of under-five children and 61.8% of their mothers were VA-deficient according to serum retinol concentrations 4.

Large scale periodic supplementation of under-five children with high-dosage VA capsules is still the preferred VA strategy in most developing countries (DCs) 5. Several studies have shown the efficacy of community- or hospital-based VA supplementation 267. However, it should only be a short-term approach to control the deficiency as it is not sustainable. Supplementation tends to entertain dependency and to convey the idea that VA deficiency is a medical problem, not a food and nutrition problem, which it is 8. VA fortification is used as a preventive measure even in high-income countries. A severe limitation in many low-income countries is that it is hard to identify appropriate food vehicles for fortification 910. Dietary diversification is a sustainable and long-term approach to the control of VA deficiency. Dietary diversification refers to several types of food system-based interventions designed to increase the supply, distribution and consumption of VA-containing foodstuffs 11. While animal sources of VA in the form of retinol are highly bio-available, their access is often constrained by poverty. There is a wide variety of plant sources of provitamin A carotenoids, but their availability is often seasonal and their bio-efficacy may be quite low as in the case of green leaves 1213.

Red palm oil (RPO) is the highest plant source of provitamin A carotenoids, and it is highly bio-available because of the fat milieu and the absence of a plant matrix 141516. RPO is not only a source of VA; it provides fat, which is often in short supply and affects the bio-efficacy of dietary provitamin A carotenoids. RPO is also a source of several antioxidants including vitamin E and non-VA carotenoids which are involved in the prevention of cancer and other chronic diseases 171819. RPO has been shown, contrary to common belief, to have a protective role in cardiovascular disease through increasing HDL-cholesterol 2021. It is a staple fat in several countries of West, Central, and Southern Africa. However, the levels of consumption by nutritionally vulnerable groups and the extent of oil blanching, which destroys the VA activity, are by and large unknown. Many trials and a few programmes showed the efficacy and effectiveness of RPO in children and in women 2223242526272829. In Burkina Faso, it was shown in a pilot-study that it was possible through social marketing to bring people who were unaccustomed to RPO to purchase and consume it to protect women and children from VA deficiency 4. After two years of promotional activities, it was found that around 45% of women and children in the test area had consumed RPO in the week prior to the survey 30. This led to a substantial decline in the rate of low serum retinol in the study area, from 61.8% to 28.2% in mothers, and from 84.5 to 66.9% in children 4. Based on market studies, it was also concluded that in the western part of Burkina Faso, RPO could be produced in much larger amounts by women who traditionally extract the oil, provided there is a demand for the product.

Following the pilot study, a larger project was implemented and one of the components was the RPO-fortification of school meals in selected areas. The school intervention was designed as a means of improving VA status of pupils and as a channel for RPO introduction in communities. The school lunch program is a promising entry point for nutritional improvement and for reaching communities, although not all children are enrolled in school – the rate of primary school enrolment in Burkina Faso is 27% 31. The RPO retail system was developed so that the sites with the school intervention could have access to RPO through commercial channels. The purpose of this paper is to report on the impact of the school intervention on school children's retinol status.

An important finding of this study is that VA deficiency at school age is a serious public health problem in the intervention areas, since 47.2% in Kaya and 37.1% in Bogandé had low serum retinol at baseline, whereas the cut-off for a severe public health problem is 20% low serum retinol according to WHO 33. This confirms previous findings in school-children in Niger 32, with a 45% baseline rate of low serum retinol. In the 15 RPO schools in Kaya and in the 8 RPO schools in Bogandé, the rate of low serum retinol was down to 13% and 15%, respectively, so that the VA deficiency went from a severe to a moderate public health problem, after an average of 28 and 51 RPO fortified meals in Kaya and Bogandé respectively, over a year. These findings are in accordance with previous studies showing the efficacy or effectiveness of RPO among preschool children 27, pupils 34, and reproductive age women 425. As suggested by Wasanwisut 35, the intervention was considered effective since the deficiency rate was down to 15% or less in all intervention groups.

The VA supplied by the RPO supplement over the test year amounted to approximately 42 mg RAE in Kaya and 76.5 mg in Bogandé, which is close to the 60 mg provided by a single VA capsule if we use 6:1 as conversion factor for β-carotene to retinol. Had we used the newly recommended conversion factor of 12:1 36, the total amount of VA provided as RPO would have represented around half of the dosage of a VA capsule. It is interesting to note that the RPO and the single VA capsule had a nearly equivalent impact on serum retinol in Bogandé school children. RPO was not found more effective than retinol supplements in our study, however, which is at variance with others 3437. It may be simply a matter of dosage or duration of the RPO fortification in our study, or else, it may be due to the fact that the interval between VA capsule administration and the endline serum retinol measurement was slightly shorter (5 months) than the interval between the last RPO meal and the endline serum retinol measurement (5.5 – 6 months).

Mean final serum retinol in Kaya pupils was nearly twice as high as that of Bogandé RPO pupils, in spite of the fact that the former had received roughly half as much RPO as the latter. This may reflect the fact that in Kaya, pupils were still receiving RPO supplements when endline blood samples were collected for retinol determination, whereas in Bogandé, RPO supplementation was interrupted for school recess 5.5 to 6 months before blood sampling, so that VA stores could be more depleted.

In Bogandé, the rate of VA deficiency at baseline was lower than in Kaya. This is unquestionably due to the different timing of the survey, which took place in the rainy season with plenty of green leaves and mangoes in Bogandé, and during the dry and lean season in Kaya. This may also be why in Kaya, the few children who had received a VA capsule in the course of the National Micronutrient Days 6 months or more before the baseline study did not have a better VA status compared to other pupils.

In both sites, our findings support previous studies showing that initially deficient subjects derived the most benefit from the VA supplement, whether in the form of RPO or a single VA capsule 46383940. In initially deficient pupils of Bogandé, serum retinol increased by 87.5% with the VA capsule and by 63.1% with RPO meals. In VA replete subjects, there was no further increase in serum retinol; there was even a tendency for the reverse, with 12% of the normal pupils at baseline showing a low serum retinol value at endline (VA capsule or RPO treatment). Such paradoxical findings were reported previously, but with synthetic VA, not with food supplements 640. It may simply reflect regression to the mean, but further research on the potential adverse effect of VA supplementation among non-deficient children is warranted.

In Kaya and in Bogandé as well, the rate of low serum retinol remained quite high (between 13% and 17%) after the intervention, however. This high residual rate, whether with the VA capsule or RPO "treatment", again shows that a dosage of approximately 60 mg RAE sustains normal VA status for less than 6 months. Among pre-schoolers of the same Kaya area, Zagré et al 4 had reported that 6 months following a VA capsule distribution among preschoolers with a coverage rate around 90% in Burkina Faso, the rate of low serum retinol was 84.5%. In under-five children of Niger, it was shown that three months following VA capsule administration, the rate of low serum retinol was practically back to baseline level of 38% 11. Although this was not the purpose of the present study, we could observe that the benefit of VA capsules was indeed short-lived. In one of the intervention sites (Kaya), 18% of the pupils had received a VA capsule 6 months prior to our baseline survey, but their VA status was not different from that of other pupils. So providing some 60 mg of VA either through RPO fortification of school meals or through a single VA capsule over the test year only alleviates the VAD problem in school children. At least two VA capsules per year if not more, or a higher level of RPO fortification of school meals, or a combination of VA supplementation and fortification, would be required.

Factors other than VA intake may also contribute to low serum retinol values, and these should not be overlooked. One of those factors is underlying infection, which is known to reduce serum retinol 4142 and makes serum retinol non-specific of VA deficiency. We could have used a more sensitive and specific indicator of VA deficiency such as the modified relative dose-response 434445, but the required retinol analog was only available at high cost. We collected information on the occurrence of illness in the previous fortnight, but this variable showed no significant association with serum retinol at either time. Another factor that may explain the persistence of more than 10% low serum retinol values is the presence of concurrent nutritional deficiencies which may act as limiting factors. Zinc deficiency is widely prevalent among children worldwide, and it is known to affect growth 46 and to interact with VA 47. The fact that taller children had a higher serum retinol response in both areas indeed suggests that zinc or protein-energy malnutrition may interfere with VA status improvement. These observations lead to advocate for more global nutritional approaches to micronutrient malnutrition rather than single nutrients, and therefore dietary diversification strategies, along with public health measures to control infection.

Boys are reportedly at higher risk of VA deficiency 484950 although the reasons for their higher vulnerability are largely unexplained. Baseline data did not disclose a better VA status of girls, but their response to RPO in Kaya was significantly higher than that of boys. In Bogandé, sex was not a significant determinant of serum retinol in the co-variance analyses including all three treatment groups. In separate linear regression of endline or change of serum retinol for the capsule and RPO groups, it was found that female sex was associated with a higher response, with the VA capsule but not with RPO supplementation. No explanation for this difference can be proposed.

The interpretations of the findings in Bogandé were obscured by the much better VA status of the negative control group of pupils at baseline. Indeed, the rate of low serum retinol was of the same magnitude as that found in the positive control and RPO groups, but after the intervention. These wide differences underline the disparities that may be found within the population of a relatively small area. Other indices of a better socio-economic status of the negative control group pupils are their significantly higher height-for-age, and the fact that among the 8 schools selected at random to serve as controls, more than half were in villages actively involved in trade. The link between better socio-economic status and better health and nutrition status is well documented 335152. In all three school groups, BMI was lower at endline than at baseline as the last harvest had been poor, which underlines the vulnerability of the area to food insecurity.

This study disclosed a high rate of VA deficiency in school children in Burkina Faso. This is an important finding, considering that it is customary to focus on preschoolers and mothers as priority target groups for the improvement of VA status. The study also confirmed the effectiveness of RPO as a food supplement for VA in primary school pupils. RPO is a highly bio-effective source of VA, and its production can be increased even in marginal areas such as Burkina Faso. Further, its distribution could be developed at the regional level, thereby reaching other countries where VA deficiency is a public health problem. RPO is also well liked by West-African populations even if they have not been exposed to it; it was very popular among exposed pupils in this study. Furthermore, palm oil plantations, and the extraction and commercial distribution of RPO, may generate income for women who are the ones producing and selling the oil. The potential benefits of RPO for VA and for other nutritional and economic benefits in Sahelian countries is only beginning to be recognized, and the evaluation of the project in Burkina Faso has allowed to advocate for RPO as part of the national strategy 53.

The author(s) declare that they have no competing interests.

BMI, Body Mass Index; DC, Developing Country; HPLC, High Performance Liquid Chromatography; RAE, Retinol Activity Equivalents; RPO, Red Palm Oil; VA, Vitamin A.

ANZ collected the field data, as part of his research for the M.Sc. (Nutrition). HD designed the study and supervised ANZ. YMP was the co-supervisor of ANZ in the field. ITS was in charge of serum retinol determinations, and he contributed his comments on the paper drafted by ANZ, redrafted (in English) by HD, and reviewed by YMP.