February 08, 2012
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Vitamin C, Nutrition and DiseaseY. Li is a graduate student and Dr. Schellhorn is a Professor, Department of Biology, McMaster University, Hamilton, Ontario, Canada.
Most of us know about the perils of too little vitamin C from our studies of history: the stories of the explorers, sailors and colonists who, deprived of fresh fruits and vegetables on long sea voyages, developed scurvy, which often caused serious illness and death. During the period of European colonial expansion, finding a cure for scurvy was not only a major medical problem but also a military and economic imperative for any nation with global ambitions. It also proved to be difficult, despite the enormous attention devoted to it, because of medicine's poor understanding of the disease. Today we know that the answer turned out to be Vitamin C, a simple substance that not only cures and prevents scurvy but also has other potential therapeutic effects, which are still being discovered today. Vitamin C is a generic term used to describe all ascorbate compounds, including ascorbic acid, dehydroascorbic acid and ascorbate salts. (The term "vitamin" comes from "vital amine," a term coined in the early 20th century. This is somewhat of a misnomer because these we know now that these compounds do not have any amino groups. However, the term "vitamin" has gained such popularity that it has stuck.) Because of its effect against an array of diseases, vitamin C has been credited with almost magical properties. Although using it to treat diseases such as cancer and heart disease remains controversial, the importance of vitamin C in human health is universally recognized. As one authority rightly put it, "Nothing emphasizes the importance of vitamin C to human beings more than the effect of being without it for a relatively short time."(1) Animals Do It; We Can't
L-ascorbic acid, a naturally-occurring and biologically active form of vitamin C, exists as white crystals and is freely soluble in water. Most non-human animals can make their own vitamin C, but humans cannot. We must rely instead on eating foods that contain vitamin C in order to survive. This state of affairs — in effect a nutritional defect of our species — was caused by a genetic mutation estimated to have occurred around 40 million years ago.(2)
The fact that this mutation spread throughout the human population raises the question of whether or not this "nutritional defect" is associated with certain evolutionary advantages. While the answer to this question is unknown, several hypotheses have been proposed.(3)(4)(5) For example, some scientists speculate that the ultimate cause was a prehistoric viral infection that caused genetic damage which knocked out our ability to manufacture vitamin C. But because our ancestors lived in warm climates that were extremely rich in foods containing vitamin C, the nutritional consequences of this defect didn't really show up. As this theory has it, this inability to produce vitamin C internally likely caused an accumulation of free radicals within the body (as discussed below), which, in turn, resulted in an increase in the mutation rate of bodily cells, which, in turn, sped up the evolutionary transition to modern day Homo sapiens. This idea of ascorbic acid influencing the rate of mutation and, consequently, evolution is supported by the fact that increased levels of free radicals are known to promote HIV replication, whereas ascorbic acid slows down the replication cycle.6 This could be one reason why natural selection favored the loss of our ability to synthesize vitamin C, especially when vitamin C is available from diet. By reducing human longevity, the loss of vitamin C producing-ability may also have selected against aging populations and made more food available for younger and more fertile individuals within early human populations, perhaps in a time of food shortages — in effect, thinning the human herd to the ultimate benefit of the survival of the species. What Vitamin C Does for Your Body
The healing power of foods containing vitamin C had been understood long before the discovery of the vitamin itself. As early as 17th century, more than three hundred years before the chemistry of ascorbic acid was known, lemon juice was used by some to help prevent scurvy and treat the tooth loss, broken blood vessels and impaired wound healing associated with it. These symptoms are the result of a collagen deficiency brought on by a lack of vitamin C.(7)
Vitamin C affects mood and energy levels. Depression and hypochondria are common symptoms of vitamin C deficiency.(8) These are caused by norepinephrine deficiency, which results from the inadequate conversion of dopamine to norepinephrine in the absence of ascorbic acid.(9) Vitamin C deprivation often also leads to a condition that impairs fatty acid metabolism and produces fatigue and lethargy.(10) Vitamin C is also essential for the absorption of iron by our bodies. Lack of vitamin C can lead to iron deficiency anemia, which is characterized by pallor, fatigue and weakness.(11)(12)(13)(14) How We Process Vitamin C
When we take vitamin C, it is absorbed in the small intestine and enters the circulatory system from there.(15)(16)(17)While circulating in the blood, vitamin C is filtered by the kidneys. The filtered vitamin C is then reabsorbed into the blood.(18)
There are limits, however, to the amount of vitamin C that the body can process.(19)(20)(21) Excess vitamin C, as a water-soluble vitamin, is simply excreted into the urine. For this reason, taking large quantities of vitamin C orally cannot raise and maintain ascorbic acid levels in the blood. The bottom line is that vitamin C cannot be stored for long periods in our bodies. We need to take in a consistent supply of vitamin C through our diet.
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