Dr. Weil explains how vitamin D2 and vitamin D3 are different.
There are two forms of vitamin D--D2 and D3. D2 is produced by plants, is often added as fortification to foods and is common in vitamin supplements.
D3 is produced in the skin on exposure to ultraviolet light from the sun and it’s available from some animal foods and some kinds of supplements. D3 is actually the form that’s better utilized by the body, so if you are going to take supplemental vitamin D, I recommend taking vitamin D3.
About Dr. Weil, M.D.:
Dr. Andrew Weil, M.D., was born in Philadelphia in 1942, received an A.B. degree in biology (botany) from Harvard in 1964 and an M.D. from Harvard Medical School in 1968. After completing a medical internship at Mt. Zion Hospital in San Francisco, he worked a year with the National Institute of Mental Health before writing his first book, The Natural Mind. From 1971-75, as a Fellow of the Institute of Current World Affairs, Dr. Weil traveled widely in North and South America and Africa collecting information on drug use in other cultures, medicinal plants, and alternative methods of treating disease. From 1971-84 he was on the research staff of the Harvard Botanical Museum and conducted investigations of medicinal and psychoactive plants.