The practice of ingesting daily doses of vitamin C grossly in excess of the amount believed to protect against scurvy and even in excess of the amount known to produce tissue saturation is one of the more controversial aspects of current nutritional thought. The arguments for vitamin C “megatherapy” were initially outlined in the United States by Irwin Stone and later elaborated by Linus Pauling, winner of two Nobel Prizes (Hughes 1981b: 47-53). Stone disputed the adequacy of current recommended daily intakes, basing his case primarily on the rate of biosynthesis of the vitamin by animals producing their own supply and on G. H. Bourne’s estimate that the natural diet of the gorilla provides it with a daily intake of some 4.5 g ascorbic acid (Bourne 1949). His arguments for daily intakes of grams rather than milligrams were enthusiastically embraced and extended by Pauling.
Closely interwoven with the megatherapy theory is the claim that vitamin C has a number of extra-antiscorbutic functions (protection against infection and, particularly, the common cold, detoxication, cerebral function, lipid metabolism, longevity, and so forth) that might require significantly raised amounts of the vitamin (Hughes 1981b: 14-34). For example, E. Gin-ter has for many years carefully presented the thesis that vitamin C plays a part in lipid metabolism, particularly by enhancing the conversion of cholesterol to bile salts, and that it would, therefore, have a hypocho-lesterogenic function (Ginter and Bobek 1981).
To date, however, there is little evidence that these putative relationships are reflected by a specific and increased demand for vitamin C. And as indicated earlier, some of these supposed secondary roles have now been subsumed in enzymatic terms by the advances of reductionist biochemistry. Secondary (or extra-antiscorbutic) roles for vitamin C could, conceivably, require intakes greater than those necessary for the prevention of classical scurvy, but such increased requirements would, in biochemical terms, scarcely justify the massive intakes recommended by the megatherapists.
Apart from the lack of satisfactory evidence, there are other arguments against vitamin C megatherapy (Jukes 1974; Hughes 1981b: 47-53).Adverse reactions elicited by massive doses of vitamin C and the possibly toxic influence of its breakdown products could well disadvantage the body. Moreover, the ingestion of large amounts of ascorbic acid is a self-defeating exercise as the absorption of large doses is a relatively inefficient process, with less than one-half of a 1 g megadose being absorbed from the gastrointestinal tract and only one-fourth of a 5 g dose (Davies et al. 1984;“Experimental Scurvy” 1986). And, in any case, it is generally accepted that tissue saturation in humans may be satisfactorily attained by a daily intake of 100 to 150 mg or even less. The faith of the megatherapists would have appeared to blind them to the normal canons of scientific assessment.
In the mid-1970s, Pauling espoused perhaps the most controversial of all his vitamin C beliefs. In collaboration with a Scottish surgeon, Ewan Cameron, he began to write extensively on the supposed antitumor activity of vitamin C; more specifically, Cameron and Pauling published the results of a clinical trial in which it was claimed that a megadose (10 g daily) of vitamin C quadrupled the survival time of terminally ill cancer patients (Cameron and Pauling 1976). The methodology of this trial was widely criticized, and a carefully controlled attempt to repeat it at the Mayo Clinic in the United States failed to confirm the Cameron-Pauling claims. For the next 15 years, and in the face of growing reluctance on the part of the scientific press to publish his papers, Pauling continued to present his arguments for the efficacy of vitamin C in the treatment of cancer. An account of this drawn-out battle between Pauling and the American scientific establishment has recently appeared (Richards 1991).
In more general and theoretical terms, it has been suggested that the antioxidant and free-radical scavenger roles of vitamin C support its possible function in the prevention (as contrasted with the cure) of cancer. G. Block has assessed some 90 studies of cancer and vitamin C/fruit intake relationships and has concluded that there is evidence that in the majority of cancers vitamin C may have a significant prophylactic role (Block 1991). In this respect, the possible relationship between vitamin C and nitrosamine-induced cancers has attracted some attention.
It has been speculated that endogenously produced N-nitroso compounds may be important initiators of human cancers. Significant in this respect is the formation of N-nitrosamines and related compounds. Nitrosamines may be formed when nitrate, a suitable “nitrosable” amine, and bacteria coexist - as in the gastrointestinal tract. Nitrate (the main dietary sources of which are fish and root vegetables) is converted by bacterial action to nitrite, which then reacts with amines to produce carcinogenic nitrosamines. Some foods, particularly cured meat products, contain nitrosamines formed during processing.
There is evidence that vitamin C may prevent the formation of carcinogenic nitrosamines from nitrate and may even reduce the carcinogenicity of preformed nitrosamines (Hughes 1981b: 27-9; MAFF 1987). It has been suggested, for example, that a reduction in nitrosamine formation, attributable to citrus fruit vitamin C, may be a contributory factor in determining the comparatively low incidence of large bowel cancer in the “citrus belt” of the United States (Lyko and Hartmann 1980). Sodium nitrite is used in the large-scale preparation of cured meats, bacon, and sausages (primarily to prevent the activity of the highly toxic Clostridium botulinum), and these products, consequently, contain a range of preformed nitroso compounds. There may, therefore, be good scientific reasons for regarding orange juice as a useful dietary accompaniment to a fried breakfast!
World History
