Occurrence in nature Oxalic acid and oxalates are abundantly present in many plants, most notably fat hen (lamb's quarters), sour grass, and sorrel (including oxalis). The root and/or leaves of rhubarb and buckwheat are listed being high in oxalic acid.[6][7]
Foods that are edible but that still contain significant concentrations of oxalic acid include - in decreasing order - star fruit (carambola), black pepper, parsley, poppy seed, rhubarb stalks, amaranth, spinach, chard, beets, cocoa, chocolate, most nuts, most berries, and beans. The gritty “mouth feel�?one experiences when drinking milk with a rhubarb dessert is caused by precipitation of calcium oxalate. Thus even dilute amounts of oxalic acid can readily "crack" the casein found in various dairy products.
Leaves of the tea plant (Camellia sinensis) contain among the greatest measured concentrations of oxalic acid relative to other plants. However the infusion beverage typically contains only low to moderate amounts of oxalic acid per serving, due to the small mass of leaves used for brewing.
[edit] Physiological effects
The affinity of divalent metal ions is sometimes reflected in their tendency to form insoluble precipitates. Thus in the body, oxalic acid also combines with metals ions such as Ca2+, Fe2+, and Mg2+ to deposit crystals of the corresponding oxalates, which irritate the gut and kidneys. Because it binds vital nutrients such as calcium, long-term consumption of foods high in oxalic acid can be problematic. Healthy individuals can safely consume such foods in moderation, but those with kidney disorders, gout, rheumatoid arthritis, or certain forms of chronic vulvar pain (vulvodynia) are typically advised to avoid foods high in oxalic acid or oxalates. Conversely, calcium supplements taken along with foods high in oxalic acid can cause calcium oxalate to precipitate out in the gut and drastically reduce the levels of oxalate absorbed by the body (by 97% in some cases.)[8][9] The calcium oxalate precipitate (better known as kidney stones) obstruct the kidney tubules.
Oxalic acid is also biosynthesized via the metabolism of ethylene glycol ("antifreeze"), glyoxylic acid, and ascorbic acid (vitamin C). The latter pathway presents a potential health risk for long term "megadosers" of vitamin C supplements. An estimated 80% of kidney stones are calcium oxalate.[10]
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Wikipedia is my friend.... My hubby takes meds for gout which can be painful.... I didn't know though that oxalic acid has also been linked to Rheumatoid Arthritis.....