Kidney stones

A kidney stone, also known as a renal calculus (from the Latin rēnēs, "kidneys," and calculus, "pebble"), is a solid concretion or crystal aggregation formed in the kidneys from dietary minerals in the urine.

Oxalates are the cause of the majority of the kidney stones that obstruct the kidney tubules – these are usually calcium oxalate. An estimated 80% of kidney stones are formed from calcium oxalate.

Oxalate is a form of mild chelating agent. In the body, oxalic acid combines with divalent metallic cations to form crystals of the corresponding oxalates which are then normally excreted in urine as minute crystals. Oxalate solubility for metals decreases in the order Calcium > Cadmium > Zinc > (Magnesium, Nickel, Iron, Copper )> {Arsenic, Antimony, Lead} > Mercury.

Its use as a chelating agent is somewhat limited, as metals such as zinc and magnesium are fairly key to health. Where oxalate is interesting, however, is that it may be an indicator of other problems and in particular a diet too high in calcium, for example. Oxalates can deposit themselves about our bodies rather than being excreted.

The highly insoluble iron(II) oxalate, for example,  appears to play a major role in various forms of joint pain.

Oxalate occurs in many plants,. On the whole, if our mineral intake is in balance these plants will simply serve, if taken in moderation and eaten as part of a balanced diet, in removing any excess of minerals not needed. But, if we have overdosed on the minerals above to a major degree – taking supplements for example, or simply eating too much of one type of mineral rich food, the precipitation that takes place will cause the problems above.

Let us hypothesise that we have a person who eats a lot of cheese, butter, and sugar and who consumes alcohol and other sugary drinks. That is a lot of calcium and they are likely to be out of balance. Now they consume oxalate rich foods or drinks. There will be a high level of precipitation of calcium oxalate and the person may well get kidney stones.

There is absolutely nothing wrong with eating oxalate rich plants in moderation [overdose and you could leech out important minerals], but go overboard on the calcium and eat the following and you may become ill.

• Leaves of the tea plant (Camellia sinensis) contain among the greatest measured concentrations of oxalic acid relative to other plants.
• fat hen ("lamb's quarters")
• sorrel
• rhubarb
• spinach
• broccoli
• brussel sprouts
• grapefruit
• chives

Oxalate is also found in some moulds. Some fungi of the genus Aspergillus produce oxalic acid, which reacts with calcium from the blood or tissue to precipitate calcium oxalate. Aspergillus species are common contaminants of starchy foods (such as bread and potatoes), in effect mouldy starchy food can produce a lot of calcium oxalate