Vitamin D plays a major role in phosphocalcic metabolism, in the normal functioning of the immune system and in the prevention of certain forms of cancer [1] . It exists in several forms that belong to the sterol family [2] [3] . Vitamin D deficiency is a global health problem and affects a billion children and adults worldwide [4] . Although cases of rickets remain uncommon, pediatricians are often confronted with vitamin D deficiency, clinically symptomatic and more or less severe [1] . Risk factors have been identified, such as exclusive breastfeeding without vitamin D supplementation, insufficient exposure to the sun (clothing habits, customs), hyperpigmented and thick skin, low levels of maternal vitamin D during pregnancy, chronic diseases associated with fat malabsorption, etc. [2] [3] [5] . Systematic vitamin D supplementation has been implemented in most Western countries, which has drastically reduced the prevalence of this condition [6] [7] . In developing countries, such as Senegal, micronutrient deficiencies are a major public health issue. According to the Senegalese Committee for the Fortification of Foods with Micronutrients (COSFAM), in 2018, 71% of children under 5 years of age suffered from iron deficiency, 50.2% from folate deficiency and 12.1% from vitamin A deficiency [8] . In Senegal, no large-scale factual data exist on vitamin D deficiency in children. Despite the permanent sunshine throughout the year in Senegal, where the population is predominantly pigmented and thick skin, studies show that rickets due to vitamin D deficiency still poses serious health problems. Thus, in a study carried out in 2022 on rickets at the Dakar University Hospital, vitamin D deficiency represented 46.2% of the causes of rickets [9] . In addition, there are no guidelines from the Ministry of Health and Social Action (MoHSA) on vitamin D supplementation and few studies on rickets have been carried out. In this context that we carried out this study to determine the prevalence of vitamin D deficiency in children aged 6 to 59 months and to analyze factors associated with it at the Institute of Social Pediatrics in Pikine-Guédiawaye, a suburb of Dakar.

Of the 338 children surveyed, 229 were sampled and 102 analyses were received. Among them, 35 had vitamin D deficiency, representing a prevalence of 34.31%. The median age was 27.59 months [6 - 60 months]. The age group [13 - 24 months] was the most representative ( Figure 1 ). The sex ratio, in favor of boys, was 1.17.

Within the study population, 83 children (81.37%) lived in the large family home. The majority of the study population had access to water and electricity ( Figure 2 ). The family environment was unfavorable in 15.30% of cases.

The socioeconomic level was low in 44% of children and very low in 26% of children.

Before 6 months of life, 31% of children were exclusively breastfed and 51.96% were predominantly breastfed ( Table 1 ).

Mean age of diversification was 5.93 months [3 - 17 months]. Early and late dietary diversification was noted in 7.01% and 18% of children, respectively.

In the study population, 29 children (28.43%) of the population had less than 3 meals per day.

Animal proteins represented the lowest proportion of diversification foods with a rate of 7.84% ( Table 2 ).

In our study, 32.65% of children had good dietary diversification ( Table 3 ).

Mean age of weaning was 18.75 months [6 - 27 months]. Nearly half of the children (47.43%) were weaned before 16 months ( Figure 3 ).

The different forms of malnutrition, chronic or acute, and underweight were present respectively in 23.53%, 22.55% and 18.63% of children ( Table 4 ).

Vitamin D deficiency was statistically associated with the presence of acute malnutrition (p = 0.02) ( Table 5 ).

*p-value < 0.05 the significance threshold set.

In our study, more than one-third of apparently healthy children aged 6 to 59 months had vitamin D deficiency. Permanent sunshine did not prevent the occurrence of vitamin D deficiency in these children. This may be explained by the fact that thick, pigmented skin opposes good vitamin D synthesis. Indeed, patients with dark skin are also at risk of vitamin D deficiency because photosynthesis by ultraviolet rays is hindered by melanin. The role of melanin as a protective screen against the harmful effects of ultraviolet rays is not in favor of vitamin D synthesis [10] . People with light skin synthesize up to six times more vitamin D than those with dark skin, with the same sun exposure. A case-control study conducted in Nigeria found higher vitamin D levels in albino patients than in those with pigmented skin [11] . This high prevalence of vitamin D deficiency is reported in other similar studies conducted in Africa, particularly in Tanzania with a rate of 30% [12] . A literature review conducted in Africa highlighted a prevalence of 58.54% of vitamin D insufficiency, 34.18% of vitamin D deficiency and 17.31% of severe vitamin D deficiency [13] .

Lower prevalences of vitamin D levels below 50 nmol/L and below 30 nmol/L, respectively, of 7.8 and 0.6%, were found in another study conducted in Kenya, Uganda, Burkina Faso, Gambia and South Africa [14] .

This high prevalence of vitamin D deficiency in Africa and particularly in Senegal could be explained by the lack of vitamin D supplementation in children and the consumption of foods that are not fortified or deficient in vitamin D. Foods rich in vitamin D are fish such as salmon, horse mackerel, tuna, liver and eggs. In our study, only 7.84% of children consumed products of animal origin. Improving the vitamin D status of these children through systematic screening and supplementation if necessary, or even systematic, could have beneficial effects far beyond the skeletal sphere.

However, it is not certain that the levels of 25(OH)D considered “optimal” for bone and mineral metabolism in Westerners are the same as those in African populations. A cross-sectional study in the United States examined the relationships between 25(OH)D and parathyroid hormone and bone mineral density (BMD) showed that blacks and Mexican Americans had significantly lower 25(OH)D concentrations and higher PTH concentrations than whites. BMD decreased significantly when serum 25(OH)D and calcium intake decreased in whites and Mexican Americans, but not in blacks. The impact of vitamin D deficiency (25(OH)D ≤ 20 ng/ml) on PTH levels was modified by race/ethnicity [15] . Blacks have been reported to have lower serum 25(OH)D concentrations than whites [16] - [20] , primarily because increased skin pigmentation inhibits cutaneous synthesis of cholecalciferol, the metabolic precursor of 25(OH)D [10] . This has led many researchers to conclude that blacks are at higher risk of vitamin D deficiency than whites [16] - [20] and, therefore, may also be at increased risk of developing associated chronic diseases such as hypertension, diabetes, and cancer [21] [22] .

It seems desirable to take into account the ethnic origin of children to better assess vitamin D status.

Our study showed that vitamin D deficiency mainly affects infants aged 13 to 24 months with a prevalence of 41.67%. This age group corresponds to the weaning age where the majority of infants have prolonged breastfeeding and without vitamin D supplementation. In addition, breastfeeding was predominant, which, coupled with the poverty of breast milk in vitamin D, promotes vitamin D deficiency. In Senegal, supplementation is not systematic, neither in the mother nor in the infant. The ANJE (Infant and Young Child Feeding) policy recommends exclusive breastfeeding for six months then appropriate food diversification taking into account all micronutrients, including vitamin D [23] . Indeed, during diversification only 7.84% of children consumed animal proteins. However, we did not find a significant relationship between vitamin D deficiency and diversification foods. This suggests that the vitamin D deficiencies observed in this group are less related to diet than to lack of sun exposure. Indeed, we are in a society undergoing transformation where the lifestyle is becoming more Westernized with lives in poorly lit, sun-soaked apartments; children go out less and less, are transported to school by car.

Children with acute malnutrition had a higher risk of vitamin D compared to non-malnourished children (54.17% vs. 28.38%). Ba, in his work, had found that acute malnutrition was a risk factor associated with vitamin deficiency with an OR = 3.36, 95% CI (1.28 to 8.80). On the other hand, chronic malnutrition and underweight were not associated. Further studies are needed to study the relationship between the different forms of malnutrition and vitamin D deficiency [24] .