Vitamin D
Vitamin D
Snapshot
VitaminโฏD is a fatโsoluble prohormone essential for calcium and phosphorus homeostasis, bone health, immune modulation, and muscle function.
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What is Vitamin D?
VitaminโฏD refers to a group of secosteroidsโprimarily Dโ (cholecalciferol) and Dโ (ergocalciferol)โthat undergo hepatic and renal hydroxylation to form the active hormone calcitriol, which regulates gene expression via the vitaminโฏD receptor.
Where It Comes From
VitaminโฏDโ is synthesized in the skin from 7โdehydrocholesterol upon ultravioletโฏB exposure. Dietary sources include fatty fish, egg yolks, and fortified foods. Supplements provide cholecalciferol or ergocalciferol in oil, tablet, or liquid form.
Key Nutrients & Compounds
Provides vitaminโฏDโ or Dโ, which are converted to 25โhydroxyvitaminโฏD (25(OH)D) in the liver and then to active 1,25โdihydroxyvitaminโฏD (calcitriol) in the kidneys, modulating calciumโbinding proteins and parathyroid hormone activity.
Health Benefits
VitaminโฏD enhances intestinal absorption of calcium and phosphorus; supports bone mineralization and reduces fracture risk; modulates innate and adaptive immunity; promotes muscle strength and function; and may protect against chronic diseases such as osteoporosis, certain cancers, and autoimmune disorders.
Recommended Dosage
The RDA is 600โฏIU (15โฏยตg) per day for adults up to ageโฏ70 and 800โฏIU (20โฏยตg) per day for those over 70. To achieve serum 25(OH)D levels above 30โฏng/mL, supplementation of 1,000โ2,000โฏIU daily is often used, with higher therapeutic doses (5,000โ10,000โฏIU) under medical supervision.
How to Use It
Take vitaminโฏD supplements with a meal containing fat to enhance absorption. For weekly dosing protocols, divide the total weekly dose evenly. Monitor serum 25(OH)D concentrations periodically to adjust dosing and avoid toxicity.
Who Should Use It?
Individuals with limited sun exposure, older adults, those with malabsorption syndromes, darker skin pigmentation, obesity, or diets low in vitaminโฏD may require supplementation to maintain optimal status.
Possible Interactions or Cautions
Excessive vitaminโฏD can cause hypercalcemia, hypercalciuria, and soft tissue calcification. Use cautiously with thiazide diuretics or calcium supplements. Monitor serum calcium and 25(OH)D levels during highโdose therapy.
Final Thoughts
VitaminโฏD is crucial for skeletal integrity, immune health, and muscle performance. Personalized supplementation based on baseline levels and risk factors ensures sufficiency while minimizing adverse effects.
Scientific Studies
HolickโฏMF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266โ281. https://doi.org/10.1056/NEJMra070553
BischoffโFerrariโฏHA, HeaneyโฏRP, DawsonโHughesโฏB, etโฏal. Optimal serum 25โhydroxyvitamin D levels for multiple health outcomes. Adv Nutr. 2014;5(5): 658โ679. https://doi.org/10.3945/an.114.006476
MansonโฏJE, CookโฏNR, LeeโฏIM, etโฏal. Vitamin D supplements and prevention of cancer and cardiovascular disease. N Engl J Med. 2019;380(1):33โ44. https://doi.org/10.1056/NEJMoa1809944.