Vitamin D: A millenium perspective
Vitamin D is one of the oldest hormones that have been made in the earliest life forms for over 750 million years. Phytoplankton, zooplankton, and most plants and animals that are exposed to sunlight have the capacity to make vitamin D. Vitamin D is critically important for the development, growth, and maintenance of a healthy skeleton from birth until death. The major function of vitamin D is to maintain calcium homeostasis. It accomplishes this by increasing the efficiency of the intestine to absorb dietary calcium. When there is inadequate calcium in the diet to satisfy the body’s calcium requirement, vitamin D communicates to the osteoblasts that signal osteoclast precursors to mature and dissolve the calcium stored in the bone. Vitamin D is metabolized in the liver and then in the kidney to 1,25‐dihydroxyvitamin D [1,25(OH)2D]. 1,25(OH)2D receptors (VDR) are present not only in the intestine and bone, but in a wide variety of other tissues, including the brain, heart, stomach, pancreas, activated T and B lymphocytes, skin, gonads, etc.
 Global vitamin D status and determinants of hypovitaminosis D
This review describes the vitamin D status in different regions of the world with the objective of understanding the scope of hypovitaminosis D and the factors related to its prevalence that may contribute to the pathogenesis of osteoporosis and fragility fractures.
Vitamin D status has been linked to the pathogenesis of hip fractures as well as other skeletal and non-skeletal disorders. The purpose of this review is to provide a global perspective of vitamin D status across different regions of the world and to identify the common and significant determinants of hypovitaminosis D.
Six regions of the world were reviewed—Asia, Europe, Middle East and Africa, Latin America, North America, and Oceania—through a survey of published literature.
The definition of vitamin D insufficiency and deficiency, as well as assay methodology for 25-hydroxyvitamin D or 25(OH)D, vary between studies. However, serum 25(OH)D levels below 75 nmol/L are prevalent in every region studied whilst levels below 25 nmol/L are most common in regions such as South Asia and the Middle East. Older age, female sex, higher latitude, winter season, darker skin pigmentation, less sunlight exposure, dietary habits, and absence of vitamin D fortification are the main factors that are significantly associated with lower 25(OH)D levels.
Reports from across the world indicate that hypovitaminosis D is widespread and is re-emerging as a major health problem globally.
 Estimates of optimal vitamin D status
Vitamin D has captured attention as an important determinant of bone health, but there is no common definition of optimal vitamin D status. Herein, we address the question: What is the optimal circulating level of 25-hydroxyvitamin D [25(OH)D] for the skeleton? The opinions of the authors on the minimum level of serum 25(OH)D that is optimal for fracture prevention varied between 50 and 80 nmol/l. However, for five of the six authors, the minimum desirable 25(OH)D concentration clusters between 70 and 80 nmol/l. The authors recognize that the average older man and woman will need intakes of at least 20 to 25 mcg (800 to 1,000 IU) per day of vitamin D3 to reach a serum 25(OH)D level of 75 nmol/l. Based on the available evidence, we believe that if older men and women maintain serum levels of 25(OH)D that are higher than the consensus median threshold of 75 nmol/l, they will be at lower risk of fracture.
 A Short Questionnaire for Assessment of Dietary Vitamin D Intake
Aims: Dietary vitamin D intake is difficult to assess as it is irregular. In Sweden, main sourcesare oily fish, fortified dairy products and margarines. This relative validation study intends to investigate the agreement in dietary vitamin D intake between a short vitamin D questionnaire and a four day food record.
Study Design: A cross sectional study design was implemented.
Place and Duration of Study: Department of Internal Medicine and Clinical Nutrition, Sahlgrenska Academy, University of Gothenburg. Assessments were conducted between January 2009 and December 2012.
Methodology: Ninety-five female subjects (25-40 years old) performed a short vitamin D questionnaire (VDQ), covering the consumption of four foods with high vitamin D content (oily fish, milk, margarine and yoghurt/sour milk). They also performed a food record for four consecutive days in connection to the VDQ.
Results: Median (quartile 1-quartile 3) dietary vitamin D intake was 4.7 (3.6-7.4) µg/day assessed by food record and 3.4 (2.3-4.6) µg/day assessed by VDQ. The dietary intakes of vitamin D correlated significantly between methods (P=.007). The amounts of vitamin D derived from each of the four foods did not differ between methods (P>.05).
Conclusion: The short VDQ, including only four foods with high vitamin D content (oily fish, milk, margarine and yoghurt/sour milk), was able to capture the majority of the dietary vitamin D intake reported in food records. This relative validation study shows that the short questionnaire is a useful tool when assessing intake of major sources of dietary vitamin D on a group level.
 Vitamin D Status and Contributing Factors in Patients Attending Three Polyclinics in Benghazi Libya
Background: About one billion people in the world suffer from vitamin D deficiency or insufficiency. The consequences of low vitamin D level include increased risk of some cancers, cardiovascular diseases, and type one diabetes, which makes it a crucial public health concern. In spite of the imperative role of sunlight in vitamin D synthesis, recent reports have shown that higher rates of hypovitaminosis in the sunniest areas of the world. Benghazi city is sunny most of the year; there is a lack of research on Vitamin D status in Libya.
Objective: The purpose of this paper was to investigate the status of Vitamin D and the contributing factors among patients attending three out patient clinics in Benghazi.
Design: Cross-sectional study with stratified random sampling technique was used to collect patients attending three outpatient clinics in Benghazi Libya between July 1st to September 30th 2016.
Participants/Setting: All Patients attending Alkiesh polyclinic, Alfohyaht polyclinic and Yakeen Health Center were approached. 287 participants were recruited, baseline information and serum 25(OH)D concentrations were provided by 184 subjects; participation rate of 64% (58.8% females and 5.9% males).
Statistical Analyses: Description and analysis of data were carried using SPSS version 21. Level of significance was set at p value < 0.05.
 Holick, M.F., 2003. Vitamin D: A millenium perspective. Journal of cellular biochemistry, 88(2), pp.296-307.
 Mithal, A., Wahl, D.A., Bonjour, J.P., Burckhardt, P., Dawson-Hughes, B., Eisman, J.A., Fuleihan, G.E.H., Josse, R.G., Lips, P. and Morales-Torres, J., 2009. Global vitamin D status and determinants of hypovitaminosis D. Osteoporosis international, 20(11), pp.1807-1820.
 Dawson-Hughes, B., Heaney, R.P., Holick, M.F., Lips, P., Meunier, P.J. and Vieth, R., 2005. Estimates of optimal vitamin D status.
 Hedlund, L., Brekke, H.K., Brembeck, P. and Augustin, H., 2014. A short questionnaire for assessment of dietary vitamin D intake. European Journal of Nutrition & Food Safety, pp.150-156.
 Omar, M., Nouh, F., Younis, M., Younis, M., Nabil, N., Saad, M. and Ali, M., 2017. Vitamin D status and contributing factors in patients attending three polyclinics in Benghazi Libya. Journal of Advances in Medicine and Medical Research, pp.1-13.