Vitamin D is necessary for maintaining and regulating calcium levels; thus, insufficiency of vitamin D increases the risk of many chronic diseases. This study aimed to examine vitamin D levels among Jordanian and Iraqi volunteers and find the relation between vitamin D level and lipid profile patients. Vitamin D levels were evaluated using enzyme-linked immunosorbent assay. For young healthy group subjects, vitamin D levels were 20.60 ± 5.94 ng/mL for Jordanian and 27.59 ± 7.74 ng/mL for Iraqi. Vitamin D concentrations for young males and females were 25.82 ± 8.33 ng/mL and 21.95 ± 6.39 ng/mL, respectively. Females wearing hijab were 20.87 ± 6.45 ng/mL, while uncovered females were 23.55 ± 6.04 ng/mL. For >40 years Iraqi subjects, vitamin D level for healthy was 29.78 ± 9.49 ng/mL and 23.88 ± 7.93 ng/mL for hyperlipidemic subjects. Vitamin D levels for overweight and obese healthy groups were significantly higher (
Vitamin D is a fat soluble hormone that plays essential role in calcium homeostasis and mineralization of bones [
Vitamins D3 (cholecalciferol) and D2 (ergocalciferol) are metabolized in an identical manner in the liver to 25-hydroxyvitamin D [
Many studies reported that vitamin D low levels negatively affect bone mineralization causing rickets in children and osteomalacia in adults [
Besides, higher levels of 25(OH)D are associated with a healthier lipid profile [
The growing data from studies conducted on young adults, elderly persons, and youth in different countries showed that vitamin D deficiency is not recognized and is not a predominant health problem [
In Middle East countries, high variation in serum 25(OH)D levels was revealed. The lowest level of 3.6 ng/mL (9 nmol/mL) was seen in a study conducted on older persons in Saudi Arabia [
Although Oceania has a very sunny climate, studies from Australia, New Zealand, and pacific islands detected low mean 25(OH)D levels (below 20 ng/mL) and large seasonal variation was observed in volunteers in Vercargill, Dunedin, and New Zealand [
The current study seeks to determine vitamin D serum levels among healthy human volunteers living in Jordan by measuring serum levels of 25(OH)D and to examine the effect of nationality and gender on vitamin D status. In addition, we aimed to find an association between 25(OH)D levels with lipid profile results by determining 25(OH)D serum levels among hyperlipidemia Iraqi out-patients in Jordan.
This study was conducted in April 2014 in Jordan. Three hundred and ninety subjects have been enrolled in this study: 195 young (18–30 years) apparently healthy Jordanian and Iraqi subjects and 195 (>40 years) hyperlipidemic Iraqi subjects. Of the 390 subjects, 26.5% were Jordanian and 73.5% were Iraqi. As for the gender, males represent 50.25% and females were 49.75%. In addition, females were subdivided into two groups, first group (50.8%) wearing hijab (hijab is a veil that covers head, arms, and chest) and second group (49.2%) without hijab wearing modernized western style clothes.
The study protocol and the case report form were approved by the research committee (December 2013) at the Faculty of Pharmacy, University of Petra, Amman, Jordan. The case report form (CRF) was used to gather demographics, body mass index (BMI), dress style, vitamin D supplements hypolipidemic medication intake, and type of food intake. Females were categorized according to their dress style, hijab (covering all body parts except the face and hands) and western dress style. Subjects taking vitamin D supplements or under hypolipidemic medications were excluded.
Case report forms were filled by the subjects before blood sampling. Blood samples were collected using 10 mL syringes, transferred into 10 mL plane test tube, stood for clotting for 5–10 minutes, and then centrifuged (Hermle Z320, Hermle labor technique, Germany) at 5000 rpm for 5 minutes. Serum was collected in a separate tube and stored at −70°C until analysis.
Quantitative colorimetric immunoenzymatic determination of 25(OH) vitamin D concentrations in human plasma level was developed by using vitamin D ELISA kit (Diametra, Milano, Italy). The kit is a competitive solid phase enzyme-linked immunosorbent assay (ELISA). Samples were analyzed according to the manufacturer guidelines.
Vitamin D levels were classified into 3 major groups according to the classification of the Institute of Medicine (IOM) [ sufficient (>30 ng/mL); insufficient (20–30 ng/mL); deficient (<20 ng/mL).
Data from 390 subjects were expressed as mean ± SD and statistically analyzed using SPSS v. 19.0 for Windows Software Package (SPSS Inc., Chicago, IL, USA). Analytical procedures include correlation analysis to analyze demographic and clinical factors associated with vitamin D levels after logarithmic transformation. The probability value of
Table
Demographics data (age and body mass index) of all participants (
Parameter | University of Petra students |
Old Iraqi healthy individuals at Ibn Alhaytham Hospital |
Old Iraqi hyperlipidemic patients at Ibn Alhaytham Hospital |
---|---|---|---|
Mean ± SD | Mean ± SD | Mean ± SD | |
Total | |||
Age (years) |
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|
|
BMI (kg/(m2)) |
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|
|
Males | |||
Age (years) |
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|
|
BMI (kg/(m2)) |
|
|
|
Total females | |||
Age (years) |
|
|
|
BMI (kg/(m2)) |
|
|
|
Uncovered females | |||
Age (years) |
|
|
|
BMI (kg/(m2)) |
|
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|
Covered females | |||
Age (years) |
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|
|
BMI (kg/(m2)) |
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|
Distributions of participants from the University of Petra according to gender and nationality.
Sufficient > 30 | Insufficient 20–30 | Deficient < 20 | ||||
---|---|---|---|---|---|---|
Number | % | Number | % | Number | % | |
Jordanian | ||||||
Males | 4 | 7.55% | 27 | 50.94% | 22 | 41.51% |
Total females | 4 | 8.00% | 24 | 48.00% | 22 | 44.00% |
Females covered | 1 | 3.33% | 14 | 46.67% | 15 | 50.00% |
Females uncovered | 3 | 15.00% | 10 | 50.00% | 7 | 35.00% |
Iraqi | ||||||
Males | 25 | 53.19% | 18 | 38.30% | 4 | 8.51% |
Total females | 5 | 11.11% | 29 | 64.44% | 11 | 24.44% |
Females covered | 1 | 3.85% | 17 | 65.38% | 8 | 30.77% |
Females uncovered | 4 | 21.05% | 12 | 63.16% | 3 | 15.79% |
Herein, Figure
Mean value of vitamin D levels in ng/mL in University of Petra students according to their nationality.
195 (>40 years) Iraqi subjects; 78 healthy subjects; and 117 hyperlipidemic patients were enrolled in the second part of the study. The age of 78 healthy subjects ranged from 40 to 72 years with the average of
The data in Table
Distributions of participants from Ibn Alhaytham Hospital according to gender, health status, and vitamin D levels.
Sufficient > 30 | Insufficient 21–29 | Deficient < 20 | ||||
---|---|---|---|---|---|---|
Number | % | Number | % | Number | % | |
Healthy | ||||||
Males | 14 | 51.85% | 11 | 40.74% | 2 | 7.41% |
Total females | 22 | 43.14% | 21 | 41.18% | 8 | 15.69% |
Females covered | 9 | 39.13% | 8 | 34.78% | 6 | 26.09% |
Females uncovered | 13 | 46.43% | 13 | 46.43% | 2 | 7.14% |
Patient | ||||||
Males | 16 | 19.75% | 42 | 51.85% | 23 | 28.40% |
Total females | 7 | 19.44% | 18 | 50.00% | 11 | 30.56% |
Females covered | 2 | 10.00% | 12 | 60.00% | 6 | 30.00% |
Females uncovered | 5 | 31.25% | 6 | 37.50% | 5 | 31.25% |
In the current study, healthy individuals and hyperlipidemic patients were classified according to BMI into 3 major groups: normal (18.5–24.9 kg/m2), overweight (25−29.9 kg/m2), and obese (>30 kg/m2). Of the healthy individuals (
Furthermore, Table
Mean value of vitamin D levels in ng/mL for >40 years of age in healthy and hyperlipidemic Iraqi volunteers.
Category | Healthy | Patient |
|
---|---|---|---|
Vitamin D (ng/mL) | Vitamin D (ng/mL) | ||
Total |
|
|
<0.0001 |
Total males |
|
|
<0.0001 |
Total females |
|
|
0.0224 |
Normal BMI weight |
|
|
0.2208 |
Overweight ( |
|
|
0.0077 |
Obese |
|
|
0.0002 |
40–50 years |
|
|
<0.0001 |
51–60 years |
|
|
0.0027 |
Over 60 years |
|
|
0.0125 |
Herein, comparison between healthy and hyperlipidemic patients based on BMI was done and vitamin D mean level for the normal BMI healthy individuals was
The study finding revealed that vitamin D level was decreased with age in both healthy and hyperlipidemic patients as shown in Table
The finding of this study revealed that vitamin D levels are affected by many factors such as nationality, gender, sex, BMI, physical activity, and lifestyle and this was reported previously in Middle East rejoin [
Also, physical activity and lifestyle are important factors in determining vitamin D level. Herein, Figure
Regardless of the nationality, significant differences (
The age and BMI of the 195 (>40 years) Iraqi healthy and hyperlipidemic subjects from Ibn Alhaytham Hospital enrolled in the second part of the study are shown in Table
As vitamin D is a fat soluble hormone, thus adipose tissue might be a site of sequestration of vitamin D, storing and subsequently lowering circulating levels of 25(OH)D [
The inverse relationship between circulating levels of 25(OH)D with risk biomarkers and high lipid profile was detected by many studies [
In addition, age is essential factor that affects vitamin D levels like obesity, gender, and diseases. Generally, elder people are susceptible to vitamin D deficiency due to many risk factors, not only due to reduced skin production of vitamin D with age but also due to decreased sunlight exposure, decreased dietary intake, reduced skin thickness, impaired intestinal absorption, and diminished hydroxylation in the liver and kidney [
The study finding revealed that vitamin D level was decreased with age in both healthy and hyperlipidemic patients as shown in Table
The elevation of plasma vitamin D levels in the body is dependent on the vitamin D hydroxylase, vitamin D binding protein (group-specific component; GC), and the inactivation by cytochromes P450 CYP24 (or 25(OH)D-24-hydroxylase) and CYP3A4. Consequently, single nucleotide polymorphism (SNP) markers in the genes, namely, CYP2R1 and GC, might be a reason for different vitamin D levels in healthy Caucasians [
However, the incidence of vitamin D insufficiency and deficiency in Arab people is multifactorial involving gender, age, obesity, clothing, cultural behaviors, skin pigmentation, vitamin D, calcium supplements, sun exposure, and polymorphism of vitamin D receptors [
The current study showed that there was a significant difference in vitamin D concentrations between the total Jordanian and total Iraqi students and there were insignificant differences between Jordanian male and Iraqi students. Vitamin D levels also were significantly different among total Jordanian female and total Iraqi female students and the same results were detected for Jordanian hijab wearing female compared to Iraqi hijab wearing female students. A significant difference was found between Jordanian western styles wearing female students compared to Iraqi uncovered female students.
In addition, overweight and obese BMI categories showed a significant difference between healthy individuals and hyperlipidemic patients though; normal BMI category showed no significant difference between the two groups. In this study, vitamin D levels for healthy individuals were higher than vitamin D levels for hyperlipidemic patients in the three age categories. Hyperlipidemia is associated with decreased vitamin D concentrations through an unknown mechanism. Further studies are needed to replicate these data in larger populations and to elucidate the mechanisms involved in this association. Also, it is necessary to take supplements especially for those who have low plasma 25(OH)D levels related to SNPs markers of inactivating enzymes and/or vitamin D binding protein
The authors declare that there are no competing interests.
The authors would like to thank all volunteers for their cooperation and also Ibn Alhaytham Hospital.