Abstract
BackgroundVitamin D is cutaneously synthesized following sun exposure (vitamin D3) as well as it is derived from dietary intake (vitamin D3 and D2). Vitamin D2 and D3 are metabolized in the liver to 25-hydroxyvitamin D (25(OH)D). This metabolite is considered the functional indicator of vitamin D stores in humans. Since Jordan latitude is 31°N, cutaneous synthesis of vitamin D3 should be sufficient all year round. However, many indications reveal that it is not the case. Thus, this study was conducted to determine the 25(OH)D status among Jordanians.MethodsThree hundred healthy volunteers were enrolled in a cross sectional study; 201 females and 99 males. 25(OH)D and calcium concentrations were measured by enzyme linked immunosorbent assay and spectroscopy techniques, respectively. All participants filled a study questionnaire that covered age, sex, height, weight, diet, and dress style for females. Females were divided according to their dress style: Western style, Hijab (all body parts are covered except the face and hands), and Niqab (all body parts are covered including face and hands).ResultsThe average plasma 25(OH)D levels in males and females were 44.5 ± 10.0 nmol/l and 31.1 ± 12.0 nmol/l, respectively. However, when female 25(OH)D levels were categorized according to dress styles, the averages became 40.3, 31.3 and 28.5 nmol/l for the Western style, Hijab and Niqab groups, respectively. These 25(OH)D levels were significantly less than those of males (p < 0.05, 0.001, 0.001, respectively). In addition, the plasma 25(OH)D levels of the Western style group was significantly higher than those of Hijab and Niqab groups (p < 0.001). Furthermore, dairy consumption in males was a positive significant factor in vitamin D status. Even though calcium concentrations were within the reference range, the Hijab and Niqab-dressed females have significantly less plasma calcium levels than males (p < 0.01).ConclusionsVery low plasma 25(OH)D levels in females wearing Hijab or Niqab are highly attributed to low sunlight or UVB exposure. In addition, most of males (76%) and Western style dressed females (90%) have 25(OH)D concentrations below the international recommended values (50 nmol/l), suggesting that although sun exposure should be enough, other factors do play a role in these low concentrations. These findings emphasize the importance of vitamin D supplementation especially among conservatively dressed females, and determining if single nucleotide polymorphisms of the genes involved in vitamin D metabolism do exist among Jordanians.
Highlights
Vitamin D is cutaneously synthesized following sun exposure as well as it is derived from dietary intake
Vitamin D is a generic term referring to Vitamin D3 and Vitamin D2 where both are metabolized in an identical manner [3]
The aim of the present study is to determine the prevalence of vitamin D deficiency by measuring plasma levels of 25(OH)D, and to study the biological and habitual factors that might be positive predictors of vitamin D deficiency among apparently healthy people living in Jordan
Summary
Vitamin D is cutaneously synthesized following sun exposure (vitamin D3) as well as it is derived from dietary intake (vitamin D3 and D2). Vitamin D2 and D3 are metabolized in the liver to 25-hydroxyvitamin D (25 (OH)D). This metabolite is considered the functional indicator of vitamin D stores in humans. Since Jordan latitude is 31°N, cutaneous synthesis of vitamin D3 should be sufficient all year round. Because few types of food provide a natural source of vitamin D, skin synthesis is thought to constitute the major source [1,2]. Vitamin D is readily metabolized in the liver to 25-hydroxyvitamin D (25(OH)D) which is the most abundant form of vitamin D in circulation [4]. 1,25(OH)D is the biologically active form of vitamin D, it is not the ideal measure for vitamin D status. The main reasons for that is that the plasma half life of circulating 1,25(OH)D is only 4-6 hours and the circulating levels of 1,25(OH)D are thousand fold less than 25(OH)D [6]
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