Early reports in the medical literature linked kidney stone formation to serum elevations of ascorbic acid by-products. After many years of research and population studies, the link between the two is not yet completely understood. However, it is clear that there is no direct evidence that taking too much ascorbic acid results in kidney stones.
What is Ascorbic Acid?
Ascorbic acid, more commonly known as vitamin C, is a water-soluble chemical that plays many crucial roles in human physiology. Ascorbic acid is required to make collagen, the most abundant protein in the body and the primary component of connective tissue. Ascorbic acid is also needed to manufacture enzymes and to make the neurotransmitter norepinephrine. It is an important antioxidant that protects vital molecules from damage by free radicals. One of the metabolic by-products of ascorbic acid is a chemical called oxalate.
Function of the Kidneys
The kidneys are the body's filtering system. All your blood passes through the kidneys, which sense the relative proportions of different chemicals such as electrolytes. The kidneys maintain an optimal balance in the blood by retaining select chemicals and water, or excreting them in the urine. Simultaneously, the kidneys excrete waste material from normal metabolic processes. Examples of waste products are the chemicals uric acid and oxalate.
Kidney Stones
Kidney stones are hard masses composed of chemicals found in the blood and filtered out by the kidneys. These chemicals usually remain dissolved in the urine, but in some people they precipitate and from crystals instead of being excreted. If small enough, the crystals can pass through the urinary system for excretion. But sometimes they build up into larger masses or stones, which are harder to pass. The most common kidney stones are made of a combination of calcium and oxalate or phosphate.
Kidney Stone Formation
Oxalate is normally excreted by the kidneys as urinary waste. However, some studies suggest that too much ascorbic acid can elevate blood oxalate levels. It has long been assumed that this was the reason calcium oxalate stones developed. However, according to the Linus Pauling Institute, this assumption has little scientific evidence to support it. The Insitute claims that the documented benefits of ascorbic acid, even at doses of 2 g per day, far outweigh any adverse effects, and that the correlation of ascorbic acid intake and kidney stones is unfounded.
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