Life on earth is remarkably self similar at a cellular level.  From a macroscopic view there is great diversity among all creatures large and small but there is actually far more in common between us at a cellular level than is different. To see this we have to take a microscopic, even molecular point of view. For instance, all living things on this planet are made of the same chemicals  or basic building blocks. The same proteins, vitamins and minerals comprise all living creatures from a blade of grass to the cow that eats it. We all have a genetic code that determines our overall size, shape and other basic features. This genetic code is made of the same basic nucleotides, adenine, guanine etc. Would you believe that we are 80% genetically similar to an orchid? From the outside this similarity would seem impossible but at a cellular and molecular level we posses many of the same basic cellular subcomponents and produce many of the same enzymes. The mitochondria that burn sugar and make ATP to fuel chemical reactions and provide energy throughout the orchid cell are the same as the mitochondria of our cells and perform the same critical physiological function.

Among mammals the types of nutrients we can make in our own bodies is very similar. The nutrients that we are unable to manufacture for ourselves but are still required for life are called essential nutrients. These are nutrients that we must receive from our diets. The required essential nutrients among mammals are very similar with few exceptions. For example, all mammals except for cats can produce their own amino acid leucine. However, luckily for the cat this amino acid is found in great abundance in meat. Cats being carnivores,  have little problem compensating for their inability to produce this amino acid in their own bodies because they get plenty from their meat abundant diet.

Collagen is the principle structural macromolecule of all animals.  It is made primarily from two amino acids proline and lysine and they are critical for the synthesis and repair of this principle structural macromolecule that is a major component of our blood vessels. Mammals can produce their own amino acid proline but cannot make lysine. This means they must acquire lysine from their diets. As we have discussed before, Vitamin C is a crucial catalyst for the formation of collagen as well.  For all animals, vitamin c, lysine and proline are critical for collagen formation.  Most of  them are able to compensate for not being able to manufacture lysine because they each a raw diet rich in this amino acid.  Humans however,  are unable to manufacture two of these key ingredients rather than just one.

In the case of vitamin C, humans are a rare exception among mammals in that we cannot manufacture our own vitamin C any longer unlike 99.9% of the other mammals found in nature. We share this inability with guinea pigs other higher primates and a small selection of other mammals in the wild. For most animals there is only one essential nutrient for the construction and maintenance of collagen and that is  lysine. For we humans, lacking the ability to synthesize our own vitamin C, we need to acquire both of these nutrients from our diet in order to repair and maintain the healthy collagen of the blood vessels and thereby prevent and reverse the effects of atherosclerosis.   Dr. Pauling felt that these two nutrients were so critical to the natural reversal of  atherosclerosis that the two of them alone in 5 gram daily doses would be sufficient to prevent and reverse heart disease.