Dietary supplement be obtained from the diet. The term is conditional both on the circumstances and on the particular organism. For example, ascorbic acid (vitamin C) is a vitamin for anthropoid primates, humans, guinea pigs and bats, but not for other mammals. Vitamin D is not an essential nutrient for people who get sufficient exposure to ultraviolet light, either from the sun or an artificial source, as then they synthesize vitamin D in skin. Humans require thirteen vitamins in their diet, most of which are actually groups of related molecules, "vitamers", (e.g. vitamin E includes tocopherols and tocotrienols, vitamin K includes vitamin
Vitamin C had proven this, but published the result without giving Szent-Györgyi credit for it. This led to a bitter dispute over priority. In 1933, Walter Norman Haworth chemically identified the vitamin as -hexuronic acid, proving this by synthesis in 1933. Haworth and Szent-Györgyi proposed that L-hexuronic acid be named a-scorbic acid, and chemically -ascorbic acid, in honor of its activity against scurvy. The term's etymology is from Latin, "a-" meaning away, or off from, while -scorbic is from Medieval Latin "scorbuticus" (pertaining to scurvy), cognate with Old Norse "skyrbjugr", French "scorbut", Dutch "scheurbuik" and Low German "scharbock". Partly for this discovery,