The Chemistry of Vitamin D: Synthesis, Metabolism, and the Paradox of Deficiency in Sun-Rich Countries
Al-Johani, A., Alenzi, A., Aldossari, A., Alrowaily, R., Alanazi, M., Alkhadrawi, M., Alfardan, A., Alsumali, A., Alrashidi, W., Alanazi, A., Alanazi, M., Alyamani, I., Almontashiri, M., Alqurashi, S., Alsomali, M., Alrwis, A., Hudays, H. (2025). The Chemistry of Vitamin D: Synthesis, Metabolism, and the Paradox of Deficiency in Sun-Rich Countries. EKB Journal Management System, (), -. doi: 10.21608/ejchem.2025.419720.12275
Adel Zaidan Masoud Al-Johani; Ali Saleh Alenzi; Arwa Khalid Aldossari; Rimah Ali Alrowaily; Maha Alanazi; Mariam Alkhadrawi; Abrar Alfardan; Ayan Mohammed Alsumali; Wedad Mohammed Alrashidi; Abdulrahman Rashed Alanazi; Mohammed Ayyat Alanazi; Ibrahim Mohammed Alyamani; Mohammad Hamed Almontashiri; Saud Mohsen Alqurashi; Manal Salem Alsomali; Abdullah Saad Alrwis; Hussain Abdullah Yahya Hudays. "The Chemistry of Vitamin D: Synthesis, Metabolism, and the Paradox of Deficiency in Sun-Rich Countries". EKB Journal Management System, , , 2025, -. doi: 10.21608/ejchem.2025.419720.12275
Al-Johani, A., Alenzi, A., Aldossari, A., Alrowaily, R., Alanazi, M., Alkhadrawi, M., Alfardan, A., Alsumali, A., Alrashidi, W., Alanazi, A., Alanazi, M., Alyamani, I., Almontashiri, M., Alqurashi, S., Alsomali, M., Alrwis, A., Hudays, H. (2025). 'The Chemistry of Vitamin D: Synthesis, Metabolism, and the Paradox of Deficiency in Sun-Rich Countries', EKB Journal Management System, (), pp. -. doi: 10.21608/ejchem.2025.419720.12275
Al-Johani, A., Alenzi, A., Aldossari, A., Alrowaily, R., Alanazi, M., Alkhadrawi, M., Alfardan, A., Alsumali, A., Alrashidi, W., Alanazi, A., Alanazi, M., Alyamani, I., Almontashiri, M., Alqurashi, S., Alsomali, M., Alrwis, A., Hudays, H. The Chemistry of Vitamin D: Synthesis, Metabolism, and the Paradox of Deficiency in Sun-Rich Countries. EKB Journal Management System, 2025; (): -. doi: 10.21608/ejchem.2025.419720.12275

The Chemistry of Vitamin D: Synthesis, Metabolism, and the Paradox of Deficiency in Sun-Rich Countries

Egyptian Journal of Chemistry
Articles in Press, Accepted Manuscript, Available Online from 02 November 2025
Document Type: Review Articles
DOI: 10.21608/ejchem.2025.419720.12275
Authors
Adel Zaidan Masoud Al-Johani* 1; Ali Saleh Alenzi1; Arwa Khalid Aldossari1; Rimah Ali Alrowaily1; Maha Alanazi1; Mariam Alkhadrawi1; Abrar Alfardan1; Ayan Mohammed Alsumali1; Wedad Mohammed Alrashidi1; Abdulrahman Rashed Alanazi1; Mohammed Ayyat Alanazi1; Ibrahim Mohammed Alyamani1; Mohammad Hamed Almontashiri1; Saud Mohsen Alqurashi1; Manal Salem Alsomali1; Abdullah Saad Alrwis2; Hussain Abdullah Yahya Hudays2
1Ministry of National Guard, Saudi Arabia
2King Khalid University Hospital, King Saud University
Abstract
Vitamin D, a secosteroid hormone, has a core role in calcium homeostasis and bone health, with recent studies suggesting its role in immune function, cardiovascular health, and cancer prevention. Its peculiar mechanism of synthesis, initiated by solar ultraviolet B (UVB) radiation in the skin, renders it an important interface between environmental exposure and biochemical regulation. In this review, we detail the intricate photochemistry of cutaneous vitamin D synthesis from its precursor 7-dehydrocholesterol through pre-vitamin D3 formation and its subsequent thermal isomerization. We then detail the enzymatic hydroxylation cascade in the liver and kidney, controlled by cytochrome P450 enzymes (CYP2R1 and CYP27B1), that produces the biologically active hormone, 1,25-dihydroxyvitamin D [1,25(OH)2D]. The main paradox discussed is the prevalence of vitamin D deficiency and insufficiency that is widespread and often high in populations residing in sun-rich geographical regions. This review synthesizes current evidence to describe the chemical, behavioral, and environmental determinants of this paradox, including the UVB-absorbing properties of melanin, the photolytic degradation of vitamin D and its precursors, clothing and sunscreen use, cultural practices, atmospheric pollution, and adiposity. We deduce that the simplistic equating of abundant sunshine with vitamin D sufficiency is both chemically and biologically naive, and public health policy must evolve to address this complex interplay of influences in order to reduce the health burden of widespread hypovitaminosis D.
Keywords
Vitamin D; photochemistry; calcium homeostasis; chemical; behavioral; environmental factors; hypovitaminosis D
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