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Vitamin D

FAT-SOLUBLE

Cholecalciferol (D3), Ergocalciferol (D2)

Vitamin D is unique among vitamins because it can be synthesized by the human body through the action of sunlight on skin, earning it the moniker "the sunshine vitamin." It functions as a prohormone — the body converts it into an active hormone (calcitriol) that regulates calcium and phosphate homeostasis. Its classical function is promoting bone mineralization, but vitamin D receptors are expressed in virtually all tissues, suggesting roles in immune function, muscle strength, and cardiovascular health.

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Key Functions

  • Calcium and phosphorus homeostasis
  • Bone mineralization and growth
  • Immune system modulation
  • Muscle function and strength
  • Cell growth regulation

Best Food Sources

Fatty fish (salmon, tuna, mackerel)Egg yolksFortified milk and orange juiceCod liver oilUV-exposed mushrooms

Deficiency: Rickets (children) / Osteomalacia (adults)

  • Bone deformities (bowed legs)
  • Bone pain and tenderness
  • Muscle weakness
  • Increased fracture risk
  • Delayed growth in children

High-Risk Groups

  • Breastfed infants without supplementation
  • Elderly adults
  • Dark-skinned individuals at high latitudes
  • Those with limited sun exposure

Sources

Reviewed for accuracy: Content is based on guidelines from the NIH Office of Dietary Supplements, Harvard T.H. Chan School of Public Health, and peer-reviewed medical literature.

Recommended Daily Amount

Adult Men

15 mcg (600 IU) age 19-70; 20 mcg (800 IU) age 71+

Adult Women

Same as men

Upper Limit (Tolerable)

100 mcg (4,000 IU)

Did You Know?

Approximately 1 billion people worldwide have low vitamin D status, making it one of the most common nutritional deficiencies.

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