If you've ever passed a kidney stone, you do not want to repeat the experience! The sharp and irregular stones travel down the slender tube (ureter) leading from the kidney to the bladder, and from the bladder to the urethra, following the path by which urine exits the body. While tiny stones may pass unnoticed, a larger stone can induce some of the worst pain that humans experience.

Most kidney stones are composed of calcium and oxalic acid, substances present in the urine that can crystallize inside the kidneys. Although these chemicals occur in everyone's urine, our natural biochemistry is usually able to prevent them from crystallizing. However, sometimes these protective methods fail and a stone develops. This article focuses mainly on these calcium oxalate stones.

Less commonly, kidney stones may be made from calcium and phosphate, from another substance called struvite (usually the result of an infection) or, rarely, from uric acid or cystine.

It isn't known why some people develop kidney stones and others do not. However, once you've had a stone, you are fairly likely to develop another.

Low fluid intake greatly increases the risk of developing virtually all types of stones.1,2,3For this reason, individuals at risk of developing stones are often advised to increase their fluid intake. However, while there is evidence that fluids in the form of coffee, tea, beer, and wine can decrease risk of kidney stone development, apple juice and grapefruit juice may have the opposite effect.4,5

High intakes of sodium 6,7and protein (particularly animal protein) may also increase the risk of calcium oxalate stones,8,9although some studies have found that protein has no such effect.10 Oxalate-rich foods, such as spinach, rhubarb, and cocoa may also increase the risk of developing calcium oxalate stones. Indirect evidence suggests that regular use of cranberry concentrate tablets might also increase risk of kidney stones.11 In addition, vitamin D affects calcium levels in the body, and prolonged use of extremely excessive doses of vitamin D has been known to cause kidney stones. Strangely, however, high-calcium foods don't seem to increase the risk of calcium oxalate stones. (See Other Proposed Treatments for Kidney Stones below).

Conventional treatment for kidney stones varies depending on symptoms as well as the location and chemical composition of the stones. For those who pass a stone spontaneously, the main treatments are painkillers and fluids. The chemical composition of passed stones can be analyzed to determine their cause. Other stones may be detected earlier, when they are still in the kidney. Treatment depends on their location and symptoms. Those causing problems may be treated with extracorporeal shock-wave lithotripsy, a technique that can break up these stones from outside the body, allowing them to pass more easily. Occasionally, however, surgery may be necessary.

"Silent" stones, or those causing no symptoms, are often treated with preventive measures alone. These methods include increasing fluids, modifying the diet, and taking drugs or supplements to alter the chemistry of the urine.

Citrate

Citrate, or citric acid, is an ordinary component of our diet, present in high amounts in citrus fruits. Citrate binds with calcium in the urine, thereby reducing the amount of calcium available to form calcium oxalate stones. It also prevents tiny calcium oxalate crystals from growing and massing together into larger stones. Finally, it makes the urine less acidic, which inhibits the development of both calcium oxalate and uric acid stones.

What Is the Scientific Evidence for Citrate?

One form of citrate supplement, potassium citrate, was approved by the FDA in 1985 for the prevention of two kinds of kidney stones: calcium stones (including calcium oxalate stones) and uric acid stones.

In a 3-year, double-blind study of 57 people with a history of calcium stones and low urinary citrate levels, those given potassium citrate developed fewer kidney stones than they had previously. In comparison, the group given placebohad no change in their rate of stone formation.12

Potassium-magnesium citrate was studied in a 3-year trial involving 64 participants with a history of calcium oxalate stones.13During the study, new stones formed in only 12.9% of those taking the potassium-magnesium citrate supplement, compared to 63.6% of those taking placebo. Benefits have been seen in other small studies as well.56,60

Citrate is available in the form of calcium citrate. Besides increasing citrate in the urine, this supplement has the advantage of being a readily absorbed form of calcium for those seeking to increase their calcium intake for other health reasons.14 However, calcium citrate has not yet been studied as a preventive for kidney stones.

Some physicians have proposed drinking citrus juices as a means of increasing urinary citrate levels. Like potassium citrate, orange juice decreases urinary acidity and raises urinary citrate, but it also raises urinary oxalate, which might tend to work against its beneficial effects.15Lemon juice may be preferable, as it has almost five times the citrate of orange juice. A small study found that drinking 2 liters of lemonade daily doubled urinary citrate in people with decreased urinary citrate.16Avoid regular consumption of grapefruit juice, though: in one large-scale study, women drinking 8 ounces of grapefruit juice daily increased their risk of stones by 44%.17

It was first thought that citrate supplements were only helpful against kidney stones in individuals who didn't excrete the normal amount of citrate in their urine.18However, some researchers now suggest that citrate treatment may also be useful for those at risk for stones whose citrate excretion is normal.19

Dosage

The proper dosage of citrate depends on the chemical form and should be individualized under medical supervision.

Safety Issues

Potassium citrate can irritate the gastrointestinal tract, causing upset stomach or bloating in 9% to 17% of people.20Potassium-magnesium citrate may potentially cause the same problem, although one study found it to be no more irritating than placebo.21

Supplements containing potassium have the potential to raise blood levels of potassium too high, primarily in people with impaired kidneys or those taking a potassium-sparing diuretic such as triamterene. Taking too much citrate can also result in overly alkaline blood, again particularly in people with kidney disease.

Citrate-induced reduction of urinary acidity can lead to decreased blood levels and effectiveness of numerous drugs, including lithium, methotrexate, oral diabetes drugs, aspirin and other salicylates, and tetracycline antibiotics.22 In addition, the urinary antiseptic methenamine is less effective in alkaline urine. Conversely, the blood levels of other drugs could increase, possibly increasing risk of toxicity. These drugs include stimulants, such as ephedrine and methamphetamine, as well as the drugs flecainide and mecamylamine.