Why Can't Humans Make Their Own Vitamin C?

Why can't humans make their own vitamin C? Almost every animal can: dogs, cats, goats, even mice. You can't, because of a broken gene in your DNA that stopped working about 60 million years ago. From sailors whose old wounds reopened at sea and the 1747 experiment that found the cure, to a lucky guinea pig discovery, the GULO gene we share with apes, red blood cells that recycle vitamin C, the Inuit diet, and the truth about vitamin C and colds, this is the evolutionary story of scurvy and the vitamin your body can't make. In this video: 0:00 Why can't you make vitamin C? 0:25 What vitamin C does for your body 1:08 When old wounds reopen 1:53 The disease that killed millions of sailors 2:24 The cure that was forgotten 2:56 One of the first medical experiments 3:47 The guinea pig clue 4:29 Your broken vitamin C gene 5:37 Other animals that lost it too 5:56 Myth: the broken gene is a defect 6:42 Did losing it actually help? 7:16 Your blood recycles vitamin C 8:04 How the Inuit avoided scurvy 9:13 Myth: vitamin C megadoses stop colds 10:15 Scurvy today 10:49 So why can't humans make vitamin C? This video is for education only and is not medical advice. If you're worried about your diet or symptoms like bleeding gums, unusual bruising, or wounds that won't heal, talk to a doctor. Sources: Walter (1748) — A Voyage Round the World in the Years 1740–44 by George Anson Bown (2003), Thomas Dunne Books — Scurvy: How a Surgeon, a Mariner, and a Gentleman Solved the Greatest Medical Mystery of the Age of Sail Cartier (1545) — Account of the second voyage to Canada, 1535–1536 Lind (1753) — A Treatise of the Scurvy Holst & Frølich (1907), Journal of Hygiene — Experimental studies relating to ship-beri-beri and scurvy Nishikimi et al. (1994), Journal of Biological Chemistry — Cloning and chromosomal mapping of the human nonfunctional gene for L-gulono-gamma-lactone oxidase Drouin, Godin & Pagé (2011), Current Genomics — The genetics of vitamin C loss in vertebrates Bánhegyi et al. (1997), Free Radical Biology and Medicine — Ascorbate metabolism and its regulation in animals Milton (1999), Nutrition — Nutritional characteristics of wild primate foods: do the diets of our closest living relatives have lessons for us? Montel-Hagen et al. (2008), Cell — Erythrocyte Glut1 triggers dehydroascorbic acid uptake in mammals unable to synthesize vitamin C Fediuk et al. (2002), International Journal of Circumpolar Health — Vitamin C in Inuit traditional food and women's diets McClellan & Du Bois (1930), Journal of Biological Chemistry — Prolonged meat diets with a study of kidney function and ketosis Pauling (1970), W. H. Freeman — Vitamin C and the Common Cold Hemilä & Chalker (2013), Cochrane Database of Systematic Reviews — Vitamin C for preventing and treating the common cold Cave Logic explains why you're still wired for the Stone Age. New videos three times a week. Subscribe if you've ever wondered why humans are like this. #VitaminC #HumanEvolution #CaveLogic