Vitamin D is a fat-soluble vitamin that is naturally present in very few foods and added to others through fortification. Vitamin D is also produced within the cell when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis.3 The skin synthesis is reduced by clothing, sunscreen, air pollution, older age, darker skin pigmentation, being indoors, winter season, and higher latitude.
Unfortunately, too many Americans are not getting enough of this important nutrient so supplementation is often recommended. Vitamin D supplements are available in two forms. Vitamin D2, or ergocalciferol, is plant-derived, while vitamin D3, cholecalciferol, is animal-derived. Vitamin D3 is more effective than vitamin D2 at raising and maintaining adequate levels of circulating vitamin D in the body.2†