Almost all D’s on the market are nature-identical synthesized forms. D3 and D2 are both naturally occurring in foods, but in supplements the same forms are usually from synthesized sources. So D3 synthesized from sheep lanolin is no more natural than D2 from plants or fungi. In fact, the D3 made in the skin-liver-kidneys from cholesterol and sunlight is also literally synthesized. Either plant sterols or animal sterols (cholesterol in humans, lanolin from sheep) are irradiated with UV-B light to make D2 or D3, respectively. It is a synthetic process, either internally or to produce the supplemental form; in much the same way that vitamin C can be synthesized by most mammals (not humans) from blood glucose in a process that mirrors the commercially synthesized nature-identical form. By the way, Vitamin K is also synthesized as the exact same form found in green foods (K1). Fermented foods like cheese can also contain K2 (MK-4), which is synthesized by microbes like bacteria.