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. 1,25(OH)2D is one of the most potent substances to inhibit proliferation of both normal and hyperproliferative cells and induce them to mature. It is also recognized that a wide variety of tissues, including colon, prostate, breast, and skin have the enzymatic machinery to produce 1,25(OH)2D. 1,25(OH)2D and its analogs have been developed for treating the hyperproliferative disease psoriasis. Vitamin D deficiency is a major unrecognized health problem. Not only does it cause rickets in children, osteomalacia and osteoporosis in adults, but may have long lasting effects. Chronic vitamin D deficiency may have serious adverse consequences, including increased risk of hypertension, multiple sclerosis, cancers of the colon, prostate, breast, and ovary, and type 1 diabetes. There needs to be a better appreciation of the importance of vitamin D for overall health and well being. J. Cell. Biochem. 88: 296–307, 2003. © 2002 Wiley‐Liss, Inc.
 Update in Vitamin D
The past decade, particularly the last 18 months, witnessed a vigorous increase in interest in vitamin D from both the lay and biomedical worlds. Much of the growing interest in vitamin D is powered by new data being extracted from the National Health and Nutrition Examination Survey (NHANES). The newest statistics demonstrate that more than 90% of the pigmented populace of the United States (Blacks, Hispanics, and Asians) now suffer from vitamin D insufficiency (25-hydroxyvitamin D <30 ng/ml), with nearly three fourths of the white population in this country also being vitamin D insufficient. This represents a near doubling of the prevalence of vitamin D insufficiency seen just 10 yr ago in the same population. This review attempts to provide some explanation for: 1) the rapid decline in vitamin D status in the United States; 2) the adverse impact of vitamin D insufficiency on skeletal, infectious/inflammatory, and metabolic health in humans; and 3) the therapeutic rationale and reliable means for vigorous supplementation of our diets with vitamin D.
 Vitamin D physiology
Vitamin D3 is synthesized in the skin during summer under the influence of ultraviolet light of the sun, or it is obtained from food, especially fatty fish. After hydroxylation in the liver into 25-hydroxyvitamin D (25(OH)D) and kidney into 1,25-dihydroxyvitamin D (1,25(OH)2D), the active metabolite can enter the cell, bind to the vitamin D-receptor and subsequently to a responsive gene such as that of calcium binding protein. After transcription and translation the protein is formed, e.g. osteocalcin or calcium binding protein. The calcium binding protein mediates calcium absorption from the gut. The production of 1,25(OH)2D is stimulated by parathyroid hormone (PTH) and decreased by calcium. Risk factors for vitamin D deficiency are premature birth, skin pigmentation, low sunshine exposure, obesity, malabsorption and advanced age. Risk groups are immigrants and the elderly.
 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 Receptor BsmI Gene Polymorphisms and Gestational Diabetes Mellitus: A Saudi Study
Background: Both vitamin D deficiency and Gestational diabetes (GDM) are common among Saudis. The vitamin D receptor (VDR) gene is a candidate gene for susceptibility to several diseases. Studies on association between VDR polymorphisms and risk of GDM in Saudi populations are yet inconclusive.
Objective: to evaluate the association between Vitamin D receptor gene polymorphisms and genetic susceptibility to gestational diabetes (GDM) in pregnant Saudis.
Subjects & Methods: thirty pregnant Saudi women with diabetes (17 GDM and 13 type 2 diabetes (T2DM) with past history of GDM) were compared to 14 pregnant women with normal glucose tolerance. Patients and controls were recruited at their third trimester from Taibah University medical unit from January to July 2010. Genomic DNA was extracted and the genotyping related to vitamin D receptor BsmI gene single – nucleotide polymorphisms was carried out by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis.
Results: The gene frequency, allele frequency and carriage rate of the VDR polymorphism BsmI did not differ between patients and controls with no significant association with any clinical parameters. The 25 hydroxyl Vitamin D level but not the gene frequency was a significant predictor of history of abortion among diabetics (OR=-0.29, 95% CI -0.081-0.0, p=0.047).
Conclusions: Vitamin D receptor BsmI gene polymorphisms is not associated with gestational diabetes among Saudis. Further studies of other Vitamin D receptor gene polymorphism in combination are required.
 Holick, M.F., 2003. Vitamin D: A millenium perspective. Journal of cellular biochemistry, 88(2), pp.296-307.
 Adams, J.S. and Hewison, M., 2010. Update in vitamin D. The Journal of Clinical Endocrinology & Metabolism, 95(2), pp.471-478.
 Lips, P., 2006. Vitamin D physiology. Progress in biophysics and molecular biology, 92(1), pp.4-8.
 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.
 Tawfeek, M.A., Habib, F.A. and Saultan, E.E.M., 2011. Vitamin D receptor BsmI gene polymorphisms and gestational diabetes mellitus: a Saudi study. Journal of Advances in Medicine and Medical Research, pp.459-468.