Calcium does not dissolve very well in water. This creates a problem in metabolism. Calcium deposits can accumulate in various places in the body creating problems. Included is arteriosclerosis, where both calcium and fats accumulate in white blood cells which attach to the walls of arteries.

Calcium is held in solution by chelating agents such as citric acid. Organic acids usually have a carboxyl group attached. The carboxyl group is the same as carbon dioxide attached to other carbon atoms. This group has two oxygens which are quite negatively charged. The negative charge is drawn to the positive charge of metals, which holds metals in solution. Health food stores mostly sell calcium as calcium citrate, because citric acid has three carboxyl groups which hold the calcium in solution.

Very early in biological evolution animals would have evolved the use of ascorbic acid (vitamin C) as a combination chelating agent and antioxidant. Glucose is the starting point for biosynthesis of ascorbic acid, and it is readily available in all cells. The soft-bodied fish of Precambrian times probably evolved the synthesis of ascorbic acid from glucose around 600 million years ago. Or, the blue-greens (tiny algae) might have evolved the synthesis of ascorbic acid, and soft-bodied fish picked up the genes through horizontal gene transfer.

At the time dinosaurs died out, 65 million years ago, all biology changed. The nonwoody brush which dinosaurs ate was mostly replaced by flowering and woody plants, while mammals became complex and diversified. The new plants produced significant amounts of ascorbic acid, which eventually resulted in monkeys losing their ability to synthesize ascorbic acid.

Genes which are not being used become nonfunctional. This effect is noticeable in microbiology laboratories, where microbes rapidly lose genes which are not used under laboratory conditions. In this way, monkeys lost their ability to produce ascorbic acid, because the genes involved were not needed when their food contained large amounts of ascorbic acid.

Later, the great apes shifted to high protein diets, which caused them to evolve into humans. At first, the proteins would have been found along the coast of South West Africa, where a large number of ocean birds were nesting. The bird eggs would have been easy pickings for the great apes. Then other sources of proteins including birds, muscles and clams would have been exploited by the great apes.

Edible plants would not have been located near the coastal sources of protein. As a result, the evolving apes would not have had a plentiful source of ascorbic acid. There would have been small amounts of ascorbic acid in the bird eggs and sea food, which would prevent scurvy, but not enough to function effectively as a chelating agent for holding calcium in solution.

So the evolving apes would have acquired a problem with calcium sticking to their arteries. As the apes evolved into humans, they would have moved inland and ate mixed diets of plants and animal protein. The plant food would have partially alleviated the shortage of ascorbic acid as a chelating agent for calcium. The problem of ascorbic acid and calcium would have varied with the amount of plant food in the diets of the evolving humans.

As humans developed agriculture, diets often became over-simplified, often consisting of little more than grains, which have very little ascorbic acid. Getting enough ascorbic acid to prevent scurvy would not be difficult, but getting enough to chelate calcium would be a problem with over-simplified diets.

There are two important functions that ascorbic acid serves. It serves as a cofactor for some enzyme reactions. Cofactors are attached to proteins to facilitate metabolic reactions. Cofactors are used in very small quantities; so it is easy to get enough ascorbic acid to function as enzymatic cofactors, and this prevents scurvy. But this does not mean people are getting enough chelating agent of some sort to keep calcium in solution and prevent it from accumulating someplace.

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