Vitamin D supplements are not interchangeable, and the distinction between vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol) has real clinical consequences. Although both forms can raise measured vitamin D levels, vitamin D₃ is more potent, more stable, longer lasting, and biologically identical to the hormone the human body naturally produces. In contrast, vitamin D₂ is less effective, clears more rapidly, and may even suppress circulating vitamin D₃, undermining

Vitamin D is commonly thought of as a simple nutrient, but medically it functions as a steroid hormone with effects far beyond bone health. Unlike true vitamins, vitamin D is synthesized in the skin, activated through the liver and kidneys, and acts on receptors throughout the body to regulate gene expression. This hormonal role explains its influence on immune function, muscle strength, cardiovascular health, and brain function. Because deficiency is widespread and supplemen