Most creatures and plants synthesize their own Vitamin C - Man does Not

Vitamin C synthesis is achieved through a sequence of four enzyme-facilitated steps - which convert GLUCOSE to ascorbic acid (AA).

It is carried out:

-   In the KIDNEYS - in reptiles and birds;

-   In the LIVER - in most mammals (but not man) and perching birds; AA is converted to various mineral ascorbates.

Hypoascorbemia.   Gulonolactone oxidase (GLO - the last enzyme in the process) cannot be made by humans, since the gene for this enzyme is defective, a condition called hypoascorbemia. The generally accepted theory is that this mutation occurred to the ancestors of modern man that disabled his ability to synthesize vitamin C.

After the "Fall of man" the defective gene became significant.   Humans can obtain vitamin C (and other essential nutrients) from foods such as leaves, fruit, vegetables and meat, which after Adam and Eve were driven from the garden, mankind must now work hard to cultivate or produce, since because of sin, the ground was cursed. Presumably, it was immaterial to pre-fall Adam and Eve whether they had the GLO enzyme or not, since they had free access to the “Tree of Life” to supply all their nutritional needs. And maybe?  . . .  God caused the gene to make the GLO enzyme to be defective at the same time he cast the first couple out of the Garden, to ensure their dependency on working the ground for food. Or maybe God allowed this same gene to gradually become defunct in order to shorten man's lifespan. (Adam lived 930 years (Gen. 5:5), Noah 950 years (Gen. 9:29). After Noah the human lifespan decreased -Shem lived 600 years, Arphaxed 438 years, down through to Abraham who lived 175 years, and finally Moses who lived 120 years (Deut. 34:7)).

Vitamin C has been shown to increase longevity significantly.

The loss of the GLO enzyme needed for ascorbic acid synthesis has affected a number of species.   E.g. Some fish (E.g. rainbow trout, coho salmon), many birds (e.g. red-vented bulbul), some bats (E.g. Indian fruit-eating bat), guinea pigs, and most primates, including humans. Fortunately for the survival of these species, ascorbic acid is prevalent in surrounding food sources.