Vitamin C is so important for health that the vast majority of animals manufacture it daily in their bodies. This is why animals can live outdoors even in the winter without getting colds or most other illnesses. Being healthy is important to animals because if an animal gets sick it usually becomes eaten by a healthy animal. Only a few animals -- principally humanes, monkeys, and apes -- cannot manufacture vitamin C. The inability to manufacture vitamin C confines monkeys and apes to live in or near the tropics, where the weather is warm and edible fruits and vegetation is very rich in vitamin C and thus can supply their need for this essential nutrient. Outside the tropics they would get sick and die or be killed. When monkeys and apes are removed from the tropics to live in zoos or as pets, they are routinely fed a diet very rich in vitamin C in order to keep them healthy.
Humans also originated in the tropics and cannot manufacture vitamin C but -- unlike monkeys and apes -- most humans eventually migrated away from the vitamin C rich tropics and spread all over the world to places in which the food supply contains much less vitamin C than is needed to maintain our health. Thus, unlike other animals, we humans routinely get sick with colds and other illnesses which adequate vitamin C would protect us against. Only the invention and use of clothing, shelter, and weapons make it possible for humans to survive the illnesses caused by inadequate vitamin C which we routinely get. Humans are the only animals which routinely get sick and yet generally survive our illnesses. But why should we live with periodic bouts of illness? Why not protect ourselves by taking supplemental vitamin C? This is the argument presented in this outstanding book by the greatest chemist of the 20th century, Dr. Linus Pauling, the only person ever to have been awarded two unshared Nobel Prizes. Please acquire and read this valuable book. If you follow Dr. Pauling's advice and take supplemental vitamin C daily, you will become healthier, may never have another cold, and should be able to survive the global flu pandemic which is predicted to occur soon.
By the way, Pauling revised this book and retitled the revision Vitamin C, the Common Cold, and the Flu.