Total and free vitamin D status among apparently healthy adults living in Duhok Governorate

Suad Yousif Alkass,Noor Isam Mohammed,Masood Abdulkareem Abdulrahman

doi:10.1038/s41598-022-05775-x

Suad Yousif Alkass, Noor Isam Mohammed + Show 1 more

Open Access

https://doi.org/10.1038/s41598-022-05775-x

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Abstract

Serum total 25‐OHD is a main marker of vitamin D which represents the intake and sunlight exposure. Free form of 25‐OHD, the small fraction not bound to a transporter protein has been incorporated as a new marker. This cross-sectional study aimed to evaluate the impact of several factors on total and free vitamin D levels in healthy subjects and to find out if the free form of vitamin D could be a better representative of the body’s vitamin D status. Total and free 25‐OHD were analyzed by ELISA method in a blood sample collected from 391 apparently healthy volunteers (219 female and 172 Male) from Duhok Governorate/Iraq population. Total and free 25‐OHD levels were increased proportionally to BMI with lower values seen in the underweight group, also a significant gender differences in total D3 level with higher values in males (23.90 ± 16.41) ng/ml than females (21.24 ± 15.65) ng/ml was observed. Total and Free 25‐OHD levels were significantly associated with ages, their deficiency most frequent occurs in the younger ages between (16–25) years old. Smokers had higher level of Total 25‐OHD (26.95 ± 19.01) ng/ml and Free 25‐OHD (9.47 ± 4.94) pg/ml than nonsmokers (22.14 ± 14.59) ng/ml and (7.87 ± 4.32) pg/ml respectively. A significant increase in Free 25‐OHD level in the veiled women (9.12 ± 4.64) ng/ml than unveiled (6.16 ± 3.73) ng/ml with a significant positive correlation between Free 25‐OHD level and dress style was also seen. 30% and 33% of the participants whom their daily exposure to sunlight for 30 min and > 1 h respectively were severe deficient in total 25‐OHD. 95% of the participants who had Abnormally low level of free D were exposed for ≥ 30 min to sunlight. Daily exposure to sunlight was negatively associated with Free 25‐OHD level.

Highlights

Serum total 25‐OHD is a main marker of vitamin D which represents the intake and sunlight exposure
When the subjects were divided based on ages in this study, a non-significant variation on the mean levels of total 25-OHD (TD) and Free 25‐OHD (FD) was observed
How the TD and FD affected by different factors (Table 10), the results shows that the total was correlated to the ages and smoking factors whereas the free form was correlated to the ages, BMI, smoking, dress style and the period of exposure to sunlight

Summary

Introduction

Serum total 25‐OHD is a main marker of vitamin D which represents the intake and sunlight exposure. Free form of 25‐OHD, the small fraction not bound to a transporter protein has been incorporated as a new marker. Vitamin D levels can be investigated by the measurement of total 25-OHD (TD) which constituted about 90% of the requested determinations in the laboratory It refers to both circulating forms (25(OH)D2 and D3) of the vitamin. The measurement of bioavailable and Free 25‐OHD levels have been incorporated as new markers of vitamin D levels since 1980s but was not used regularly due to lack of its assessment method[12]. Due to their hydrophobic properties, vitamin D metabolites bind to a protein transporter called vitamin D binding protein (VDBP or DBP). It is presently unclear whether free or bioavailable 25-OHD is better reflecting the availability of 25-OHD for cells or tissues

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