[Part 4 of 4 in a series on Vitamin C and the Common Cold]
Toward the end of his book Vitamin C and the Common Cold, Linus Pauling included a chapter on human biochemical individuality. In it, he addressed the fact that every human is different, and as a result, each individual has a unique need for specific amounts of vitamin C.
Pauling pointed out that when any characteristic, such as the concentration of a certain enzyme in the red blood cells, is studied in a sample of 100 human beings, a wide range of values are invariably observed. The “normal” range is that in which 95 percent of those values lie, while the remaining 5 percent are described as abnormal. Defining normalcy on a larger scale is a bit tricky however. Pauling stated that
If we assume that 500 characters are independently inherited, then we can calculate that there is only a small chance, 10 percent, that one person in the whole population of the world would be normal with respect to each of these 500 characters.
The situation is complicated further by the fact that humans possess some 100,000 genes, each of which performs a different function. “Accordingly,” Pauling wrote, “we reach the conclusion that no single human being on earth is normal (within the range that includes 95 percent of human beings) with respect to all characters.”
Guinea pigs, like humans, are also genetically heterogeneous, as was demonstrated in a 1967 vitamin C experiment carried out by Roger J. Williams and Gary Deason of the University of Texas, Austin. The investigators obtained more than 100 young male guinea pigs, and initiated their experiment by closely observing the guinea pigs for a week while they were fed a healthy diet. This completed, the animals were then divided into eight groups of 10 to 15 animals, with each group receiving varying amounts of ascorbic acid, and one group receiving none.
Each of the guinea pigs reacted differently to the amount of ascorbic acid given to them. About 80 percent of the guinea pigs that were fed no ascorbic acid or less than 0.5 mg of ascorbic acid per kilogram of body weight per day showed signs of scurvy. Only a quarter of those receiving between 1 mg and 4 mg per kilogram per day showed signs of scurvy, while those receiving 8 mg per day or more did not show any signs of the disease. These results were in accordance with the commonly held belief that guinea pigs need about 5 mg per day of ascorbic acid in order to prevent scurvy.
However, the experiment also produced anomalies: two of the guinea pigs receiving only 1 mg of ascorbic acid per kilogram per day stayed healthy, and gained weight over the course of the eight-week experiment. One of them even gained more weight than any of the animals receiving a larger amount of vitamin C.
Strangely, seven of the animals receiving 8, 16, or 32 mg per kilogram per day were unhealthy, and did not grow very much. Five of these were then provided with 64 mg per kilogram per day, and two of them were provided with 128 mg per kilogram per day. When they were provided with larger amounts of vitamin C they began to grow at a much faster rate: initially, they had only grown about 12 grams in ten days, but during the next ten day cycle, while receiving more vitamin C, they gained an average of 72 grams each. The conclusion reached was that these seven guinea pigs, out of the thirty that were placed on between 8 mg and 32 mg per kilogram per day, possessed a larger built-in vitamin C requirement.
Williams and Deason determined that out of 100 guinea pigs, there existed a requirement range of at least 20 different levels of vitamin C. From there, the duo extrapolated that “the population of human beings is presumably not more uniform than that of guinea pigs used in their experiments, and that accordingly the individual variation in human vitamin C needs is probably just as great.”
Pauling agreed with this conclusion, adding that the requirement of ascorbic acid for humans probably ranges from 250 mg per day to 10 g per day. And he continued to make reference to biochemical individuality throughout the book, suggesting that 1 g to 2 g per day is approximately the correct amount of ascorbic acid for the average human being to ingest.