Prevalence and predictors of vitamin D deficiency in young African children

Abstract

Background Children living in sub-Saharan Africa have a high burden of rickets and infectious diseases, conditions that are linked to vitamin D deficiency. However, data on the vitamin D status of young African children and its environmental and genetic predictors are limited. We aimed to examine the prevalence and predictors of vitamin D deficiency in young African children. Methods We measured 25-hydroxyvitamin D (25(OH)D) and typed the single nucleotide polymorphisms, rs4588 and rs7041, in the GC gene encoding the vitamin D binding protein (DBP) in 4509 children aged 0–8 years living in Kenya, Uganda, Burkina Faso, The Gambia and South Africa. We evaluated associations between vitamin D status and country, age, sex, season, anthropometric indices, inflammation, malaria and DBP haplotypes in regression analyses. Results Median age was 23.9 months (interquartile range [IQR] 12.3, 35.9). Prevalence of vitamin D deficiency using 25(OH)D cut-offs of < 30 nmol/L and < 50 nmol/L was 0.6% (95% CI 0.4, 0.9) and 7.8% (95% CI 7.0, 8.5), respectively. Overall median 25(OH)D level was 77.6 nmol/L (IQR 63.6, 94.2). 25(OH)D levels were lower in South Africa, in older children, during winter or the long rains, and in those with afebrile malaria, and higher in children with inflammation. 25(OH)D levels did not vary by stunting, wasting or underweight in adjusted regression models. The distribution of Gc variants was Gc1f 83.3%, Gc1s 8.5% and Gc2 8.2% overall and varied by country. Individuals carrying the Gc2 variant had lower median 25(OH)D levels (72.4 nmol/L (IQR 59.4, 86.5) than those carrying the Gc1f (77.3 nmol/L (IQR 63.5, 92.8)) or Gc1s (78.9 nmol/L (IQR 63.8, 95.5)) variants. Conclusions Approximately 0.6% and 7.8% of young African children were vitamin D deficient as defined by 25(OH)D levels < 30 nmol/L and < 50 nmol/L, respectively. Latitude, age, season, and prevalence of inflammation and malaria should be considered in strategies to assess and manage vitamin D deficiency in young children living in Africa.

Vitamin D Deficiency and Its Association with Iron Deficiency in African Children

“…Overall median 25(OH)D concentrations were 77.6 (IQR 63.6, 94.2) nmol/L ( Table 1 ). Prevalence of vitamin D deficiency was 0.6% and 7.8% using 25(OH)D cutoffs of <30 nmol/L and <50 nmol/L, respectively, while 35.4% of children had concentrations between 50–75 nmol/L, as previously reported [ 21 ]. Since few children had 25(OH)D concentrations <30 nmol/L, only the <50 nmol/L cutoff was used for further analyses.…”

“…Nutritional deficiencies, including iron and vitamin D deficiency, are highly prevalent among young children, and little is known about their interactions in Africa where infectious diseases such as malaria are also prevalent. In the current study including 4509 children living in Africa, median 25(OH)D concentration was 77.0 nmol/L which was comparable to average concentrations in a meta-analysis of previous studies of young children in Africa (70.7 nmol/L) [ 21 ]. Low vitamin D status (25(OH)D concentrations <50 nmol/L) was associated with a 98% increased risk of iron deficiency and iron deficient children similarly had a higher prevalence of low vitamin D status.…”

“…Since inflammation alters measures of iron status and differs by vitamin D status [ 21 ], we further stratified regression analyses by the presence of inflammation and looked for interactions between inflammation and 25(OH)D concentrations in predicting iron status. We observed that 25(OH)D concentrations were highly associated with measures of iron status in the absence of inflammation in multivariable linear regression analyses ( Figure S4 ).…”

“…25(OH)D concentrations, iron markers (ferritin, hepcidin, sTfR, transferrin, iron and hemoglobin) and inflammatory biomarkers (C-reactive protein [CRP] and α1-antichymotrypsin [ACT]) were assayed as previously described [ 4 , 21 ] and are summarized in Supplementary Methods S1 . The assays showed satisfactory performances as monitored by both external quality assurance schemes (including UK National External Quality Assessment Scheme and DEQAS) and 4-hourly internal quality control assessments.…”

Vitamin D deficiency and its association with iron deficiency in African children

“…25(OH)D concentrations, iron markers (ferritin, hepcidin, sTfR, transferrin, iron and hemoglobin) and inflammatory biomarkers (C-reactive protein [CRP] and α1-antichymotrypsin [ACT]) were assayed as previously described [4,21] and are summarized in Supplementary Methods 1. The assays showed satisfactory performances as monitored by both external quality assurance schemes (including UK National External Quality Assessment Scheme and DEQAS) and 4-hourly internal quality control assessments.…”