Humans do not possess the enzyme gulonolactone oxidase necessary to make vitamin C (ascorbic acid) from glucose. Ascorbic acid is therefore a vitamin and it is essential as part of our diets. Citrus fruits are the most common ascorbic acid containing foods, but it is also present in certain vegetables such as broccoli. Ascorbic acid is most widely known for its role as an antioxidant in the body, but it does have other functions. One such function is the metabolism of histamine. Histamine triggers inflammation and causes blood vessels to become more permeable to immune cells. Ascorbic acid plays a role in this process because it is able to inhibit the action of histamine. For example, a paper published in the Journal of nutrition in 1980 demonstrated that blood ascorbic acid and histamine levels are inversely associated.
Ascorbic acid can reduce the production of histamine by inhibition of the enzyme histidine decarboxylase, which is necessary for histamine formation. Ascorbic acid can also undergo oxidation to dehydroascorbic acid, and in the process rupture the imidazole ring structure of histamine. Ascorbic acid may also enhance the production of the E series of prostaglandins which may decrease cell sensitivity to histamine. Deficiency of ascorbic acid would therefore be expected to be characterised by very high levels of histamine. This histamine would then be able to increase capillary permeability and lead to endothelial inflammation. Linus Pauling and Matthias Rath suggested that long term sub clinical ascorbic acid deficiency was able to increase the permeability of blood vessels mush like the deficiency disease scurvy. The repair mechanism for this damage is what they hypothesised, lead to the development of atherosclerosis.
Increasing the amount of ascorbic acid in the diet is a sensible step to optimum nutrition. Citrus fruits contain reasonable levels, but small amounts is present in many fruits and vegetables. However, food quantities of ascorbic acid can vary and levels are not easily calculated from our diets. Ascorbic acid is a very cheap supplement and is available universally, and so supplementation makes more sense than attempting to second guess the intake from food. Ascorbic acid has an exceptional safety record and toxicity is not known even at tens of grams a day. Linus Pauling recommended 10 to 20 grams a day in the prevention of heart disease, and most nutritionists now believe that gram amounts per day for the average adult are necessary for good health. Ascorbic acid is very cheap insurance.
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