Diary entry by Linus Pauling, 1980. The text reads: “L[inus] P[auling] / Found enzymes enthralling / He was filled with glee / By Vitamin C”[Reading Cameron and Pauling’s Cancer and Vitamin C, part 4 of 9]
In their ambitious 1979 book, Cancer and Vitamin C, Ewan Cameron and Linus Pauling argued that vitamin C possessed the ability to cure cancer. As remarkable as this suggestion was, in some respects it was almost secondary to the broader biological role that Pauling and Cameron assigned to the vitamin. As they made clear in their book, much of vitamin C’s importance could be attributed to the special way that it is made by most animals…not including ourselves.
As animals, including humans, have evolved, they have lost the ability to internally synthesize certain vital nutrients, which must now be obtained through diet alone. That said, nearly every being in the animal kingdom has retained the ability to synthesize its own vitamin C. In fact, humans are among a very small subset of animals who have lost this ability over evolutionary time, such that all of our vitamin C needs must now be met through diet. If a person does not meet this dietary need, they will develop scurvy, grow sick and eventually die. Therefore, it is paramount that humans regularly consume a baseline amount of vitamin C.
In addition to vitamin C, humans also cannot synthesize vitamins A, B1, B2, B6, and niacin, all of which are also essential for life. A deficiency in niacin, for example, can lead to pellagra, a primary disease of the skin which can result in death. Likewise, a deficiency in vitamin B1 can manifest as beriberi, a potentially fatal disease of the nervous system. But even though the absence of these nutrients will usher in dire consequences, humans have lost their ability to produce them internally.
Why is this so? The basic prevailing theory is that even though these nutrients are vital for life, food-based sources have historically been so plentiful that there was no need for the nutrients to be produced “in house.” Moreover, from an evolutionary perspective, obtaining a nutrient from a food source, rather than through self-synthesis, offers significant advantages, since it can require a lot of energy to internally produce nutrition. Once freed from the burden of self-synthesis, an organism becomes capable of applying that store of energy toward other activities.
But vitamin C seems to be a special case. Despite the evolutionary advantages of obtaining nutrition from food sources, every studied animal on Earth continues to synthesize it internally except for the following: humans, primates, guinea pigs, one species of fruit eating bat, a South Asian bird called the red vented bulbul, some grasshoppers, and fish in the trout family. For Pauling and Cameron, the tenacity with which animals have held on to the ability to produce their own vitamin C was further proof of its importance.
So again, why not humans too? Why have we lost this ability? Pauling and Cameron believed it was due to an evolutionary quirk.
As we have noted, there are evolutionary advantages to losing the ability to synthesize vitamin C. If two animals are competing for resources, the animal that is not also preoccupied with the internal process of generating its own nutrition will theoretically outcompete an opponent that is hamstrung with that energy burden. Pauling and Cameron believed that, at some point in the past, a mutant human ancestor who could not synthesize its own vitamin C successfully outcompeted other human ancestors, and was able to do so because, at that time – around 50 million years ago – its environment was abundant in vitamin C-rich foods. As the mutant bred and passed along its genetics to its progeny, its traits continued to outcompete, out-mate, and eventually eliminate vitamin C-synthesizing humans altogether. Pauling and Cameron posited that a similar situation arose with other animals, including primates, who have also lost their ability to synthesize vitamin C.
And while that idea makes intuitive sense, one still wonders why nearly all other animals have retained their capacity for vitamin C synthesis, even while losing the ability to internally produce other nutrients. The answer, according to Pauling and Cameron, is two-fold. Point one is that vitamin C is objectively important, and this special importance meant that animals tended to retain the ability to synthesize it. Crucially for humans, point two is that animals’ true need for vitamin C is far greater than what can be obtained through diet alone. In this sense, even though the human mutants were able to outcompete their synthesizing foes for a time by obtaining vitamin C through diet, maintaining that diet was not sustainable for a growing population, and perhaps the mutants never truly obtained enough vitamin C after all.
Pauling and Cameron were convinced that humans were underdosing their vitamin C, and doing so in part because of the guidance being provided by the very agency charged with providing accurate information on nutritional needs. The Recommended Daily Allowance (RDA) provided by the United States Food and Drug Administration (FDA) serves as a standard for the amount of a given nutrient that one should consume per day to maintain their health. Pauling and Cameron believed that the RDA chronically underestimated the true daily needs for specific nutrients; the recommendation for vitamin B1, for example, was about 1.5 times below optimum in their minds. In the case of vitamin C however, Pauling and Cameron believed the RDA to have been grossly underestimated at about 200 times below optimum daily need. Where once the FDA was recommending 60 mg of the nutrient per day, (bumped up to 90 mg in the year 2000) Pauling and Cameron pushed for 12,000 mg.
To determine the optimal dose of vitamin C for humans, Pauling and Cameron looked at how much vitamin C other animals synthesize, and how much dietary C the mutant human ancestor might have been expected to consume on a daily basis. For this second supposition, the researchers used data on how much vitamin C is present in specific foods and what types of foods were likely predominant when the mutant edged out its competition. The outcomes of this analysis connected with observations of contemporary primates who live in climates similar to the mutant and who ingest large amounts of vitamin C daily through their diets — volumes close to the 12,000 mg that Pauling and Cameron believed to be ideal. Finally, when analyzing the amount of vitamin C that other animals synthesize, a conjecture can be drawn about the optimal quantity for humans. A 154 pound goat, for example, could be expected to synthesize 13,000 mg per day, and other animals generated quantities that were roughly proportional to the goat by body weight.
For Pauling and Cameron, the evidence from the animal kingdom further compounded the idea that vitamin C is vital for life and that large amounts of the substance are crucial for maximizing health. But because we have lost our ability to produce our own vitamin C, most humans are living in states of suboptimal health and are exposing themselves to greater risk of affliction with serious disease. And because – as we saw in our previous post – the symptoms of scurvy closely mimic those of cancer, one might draw a connection between the two, and posit that biologically insufficient vitamin C levels are a source for increasing rates of cancer.
