Vitamin D supplements are hot—and even hotter during the shorter daylight hours of autumn and winter. Companies offer a wide range of doses and types of supplements to satisfy virtually every consumer, from infants and children to seniors. Until recently, vitamin D3 (cholecalciferol) was made only by processing sheep lanolin (the oil found in wool). Now vitamin D3 is also produced from lichen, a vegetarian source. Vitamin D2 (ergocalciferol), which is absorbed only half as well, is processed from fungi.