Vitamin D
Vitamin D
Snapshot
Vitaminβ―D is a fatβsoluble prohormone essential for calcium and phosphorus homeostasis, bone health, immune modulation, and muscle function.
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What is Vitamin D?
Vitaminβ―D refers to a group of secosteroidsβprimarily Dβ (cholecalciferol) and Dβ (ergocalciferol)βthat undergo hepatic and renal hydroxylation to form the active hormone calcitriol, which regulates gene expression via the vitaminβ―D receptor.
Where It Comes From
Vitaminβ―Dβ is synthesized in the skin from 7βdehydrocholesterol upon ultravioletβ―B 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 vitaminβ―Dβ or Dβ, which are converted to 25βhydroxyvitaminβ―D (25(OH)D) in the liver and then to active 1,25βdihydroxyvitaminβ―D (calcitriol) in the kidneys, modulating calciumβbinding proteins and parathyroid hormone activity.
Health Benefits
Vitaminβ―D 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 600β―IU (15β―Β΅g) per day for adults up to ageβ―70 and 800β―IU (20β―Β΅g) per day for those over 70. To achieve serum 25(OH)D levels above 30β―ng/mL, supplementation of 1,000β2,000β―IU daily is often used, with higher therapeutic doses (5,000β10,000β―IU) under medical supervision.
How to Use It
Take vitaminβ―D 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 vitaminβ―D may require supplementation to maintain optimal status.
Possible Interactions or Cautions
Excessive vitaminβ―D 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 highβdose therapy.
Final Thoughts
Vitaminβ―D 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
Holickβ―MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266β281. https://doi.org/10.1056/NEJMra070553
BischoffβFerrariβ―HA, Heaneyβ―RP, DawsonβHughesβ―B, etβ―al. Optimal serum 25βhydroxyvitamin D levels for multiple health outcomes. Adv Nutr. 2014;5(5): 658β679. https://doi.org/10.3945/an.114.006476
Mansonβ―JE, Cookβ―NR, Leeβ―IM, etβ―al. Vitamin D supplements and prevention of cancer and cardiovascular disease. N Engl J Med. 2019;380(1):33β44. https://doi.org/10.1056/NEJMoa1809944.