Vitamin D3 (Cholecalciferol)

An estimated 42% of American adults and over 1 billion people worldwide are vitamin D deficient, making it the most widespread nutritional deficiency on earth. D3 supplementation at 1,000-4,000 IU daily has been shown to reduce fracture risk, support immune function, and decrease all-cause mortality in large-scale meta-analyses involving over 100,000 participants.