Did you know that vitamin C isn’t essential to all animals? However, it is for us, humans. It isn’t a necessary component of diet, at least for all mammals except guinea pigs, fruit-eating bats, the red-vented bulbul bird, and primates—which includes us. All other species make their own.
They do this by converting glucuronic acid derived from glucose into ascorbic acid (C6H8O6). Three enzymes are required to make this conversion; one of these enzymes, or part of the enzyme system, is missing in primates. Irwin Stone proposed, in 1965, that a negative mutation may have occurred in these species to lose the ability to produce vitamin C. In primates, this is thought to have occurred in the region of 25 million years ago.
Unlike other vitamins, vitamin C is required in large amounts, which could only be supplied by a tropical diet high in fruit and other vegetation. If sufficient vitamin C could be obtained from such a diet, the quantity of glucose normally used to synthesize vitamin C could be channelled towards energy production. This could conceivably have been an advantage for primates or other species.
While a mere 60 mg a day can prevent scurvy, the deficiency disease first identified by Dr. James Lind in 1753, it would be illogical to assume that this is the optimal dose. A survey of doctors in the US found that those who were healthiest consumed at least 250 mg of vitamin C per day.
It is valid to infer from this brief history of evolution, a comparison with other species, and average excretion rates, that optimal vitamin C levels are probably above 1 000 mg, with plenty of room for individual variation.
What about “hard evidence”? What levels are required to ensure maximum function of enzymes and body systems dependent on vitamin C? A quick review of some of vitamin C’s hundreds of biochemical roles will help us here. Vitamin C is required for the synthesis of collagen, our intercellular glue that keeps skin, lungs, arteries, the digestive tract, and all organs intact. It is a potent antioxidant protecting against free radicals. Energy cannot be made in any cell, brain or muscle, without adequate vitamin C. The adrenal glands have a high concentration of vitamin C, which is essential for stress hormone synthesis. Vitamin C is so central in so many chemical reactions in the body that, without it, life is simply not possible.
