Common Sense Health: Facts and myths about kidney stones

By Dr. Gifford-Jones and Diana Gifford-Jones on February 14, 2025.

Margaret Thatcher, the resolute British Prime Minister known as the “Iron Lady” famously said, “You may have to fight a battle more than once to win it.” But for the millions who endure the excruciating torture of passing a kidney stone, just once is enough. About 50 per cent of those who form one stone will feel the pain again within five years. Those who develop two or more stones will form others on an average of every 2.5 years.

Kidney stones are crystals that develop on the inside lining of the kidney. The chronic irritation of these crystals may cause blood to appear in the urine. But major trouble begins when the accumulated deposit, the “stone”, breaks loose. If big enough, it becomes trapped in the ureter, the small tube that carries urine from the kidney to the bladder. Renal colic is the term used to describe the sudden, acute pain that occurs when the stone blocks the urinary tract and the muscles of the ureter contract in an attempt to move it along.

Heredity plays a major role in the formation of kidney stones. The vast majority are composed of calcium salts. These are necessary for normal body metabolism and must be flushed out in the urine every day. Due to heredity, some people absorb more calcium from food, causing a high concentration of urinary calcium and the potential for stone formation. But calcium consumption is not generally the problem. Rather, high salt intake is more frequently associated with increased stone formation. Obesity, diabetes, and recurrent urinary tract infections are also risk factors.

Treatment of kidney stones depends on the type. The less common stones of uric acid are, as stones go, rather friendly. The crystals are so soluble that even a big stone can be dissolved with oral bicarbonate (main ingredient of baking soda) and drinking plenty of water. No other stone is so cooperative, and an attack of great pain is the unwelcome onset of a crisis.

People suffering from renal colic usually require hospital treatment. With medical assistance most stones are eventually passed in the urine. Trapped stones are located by an optical instrument called the cystoscope which is inserted into the bladder. A basket-like device is then threaded up the ureter to grab the stone. If this fails surgery is required.

What else is to be avoided? It’s the use of antibiotics for longer than three weeks. This may cause an overgrowth of bacteria that possess a special enzyme, urease. This enzyme makes the urine very alkaline and may trigger the formation of struvite stones. This type of stone can fill the entire kidney causing severe renal damage.

There’s been an ongoing myth for years that large doses of vitamin C cause kidney stones. It’s hard to know how these falsehoods get started. But the very opposite is true. The fact is that vitamin C increases urine flow, results in a slightly acidic urine, and prevents calcium from binding to oxalate causing calcium oxalate stones, the most common type of kidney stone.

Experts in nutrition may know this interesting finding. In 1946, Dr. William McCormick wrote, “I have observed that a cloudy urine is generally associated with a low vitamin C status. But as soon as vitamin C is given (500 to 2,000 milligrams) the urine sediment clears in a matter of hours.”

Because of this myth some people are missing out on the other benefits of vitamin C.

Benjamin Disraeli, another former charismatic Prime Minister, once remarked, “There are three kinds of lies: lies, damned lies, and statistics.” There should be a fourth: “myths”.

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