Conditions:
Kidney Stones
Related Terms
•
Renal Calculi, Nephrolithiasis, Urolithiasis, Calcium Oxalate Stones
Principal Proposed Treatments
•
Citrate
Other Proposed Treatments
•
Magnesium, Vitamin B6, Goldenrod, Parsley, Fish Oil, GLA (Gamma-Linolenic Acid), Mesoglycan, Vitamin A, Vitamin C, Calcium
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.1,2,3 For 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 appear to have the opposite effect.4,5
High intakes of sodium6,7 and protein (particularly animal protein) may also increase the risk of calcium oxalate stones,8,9 although some studies have found that protein has no such effect.10 Oxalate-rich foods such as spinach 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.
Principal Proposed Treatments for Kidney Stones
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.
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 placebo had no change in their rate of stone formation.12
Potassium-magnesium citrate, a relatively new citrate source, was studied in a 3-year trial involving 64 participants with a history of calcium oxalate stones.13 During the study, new stones formed in only 12.9% of those taking the potassium-magnesium citrate supplement, compared to a whopping 63.6% of those taking placebo.
Citrate is also 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.15 Lemon 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 a day doubled urinary citrate in people with decreased urinary citrate.16 Avoid 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.18 However, 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.20 Potassium-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.
Other Proposed Treatments for Kidney Stones
There is some evidence that magnesium and vitamin B6 might help prevent kidney stones. Other herbs and supplements are often recommended as well, although there is little evidence that they work. Vitamin C and calcium are often said to raise the risk of kidney stones, but evidence suggests that in most (but not all) cases they might actually help prevent them.
Magnesium
Magnesium, in the form of magnesium oxide or magnesium hydroxide, may help to prevent calcium oxalate stone development. Magnesium inhibits the growth of these stones in the test tube23 and decreases stone formation in rats.24
However, human studies on magnesium have shown mixed results.25–28 In one 2-year open study, 56 participants taking magnesium hydroxide had fewer recurrences of kidney stones than 34 participants not given magnesium.29 In contrast, a double-blind (hence, more reliable) study with 124 participants found that magnesium hydroxide was essentially no more effective than placebo.30
Vitamin B6
Vitamin B6might help prevent calcium oxalate stones in certain individuals. Deficiencies in this vitamin increase the amount of oxalate in the urine of animals and humans,31 and a small uncontrolled study found that supplementation decreased oxalate excretion in people with a history of stones.32 In addition, a 14-year study of more than 85,000 women with no history of kidney stones found that women with high intakes of B6 developed fewer stones than those with the lowest intake.33 On the other hand, a large-scale study of more than 45,000 men found no link between B6 and stones.34
Miscellaneous Herbs and Supplements for Kidney Stones
In Europe, the herb goldenrod is sometimes used to help wash out kidney stones. It is believed to increase the flow of urine and therefore might help pass kidney stones and soothe inflamed tissues. However, there is as yet no evidence that it helps.
Germany's Commission E has also recommended the following herbs for kidney stones based primarily on their apparent ability to increase the flow of urine: asparagus, birch leaf, bishop's weed fruit, couch grass, parsley, horsetail, java, lovage, petasites, shiny restharrow, and stinging nettle herb and root combination.35 However, there is little to no evidence that they are really effective.
Several other supplements, including fish oil, GLA, glycosaminoglycans (GAGs), and vitamin A are sometimes recommended for kidney stones, but there is little solid evidence that they work.36–39
Vitamin C and Calcium: Help or Harm?
One of the biggest controversies surrounding the causes of kidney stones has to do with vitamin C. Concerns have been raised that long-term vitamin C treatment might increase risk of stone formation by increasing levels of oxalate in the urine, but this is controversial.40,41 In large-scale observational studies, individuals who consume large amounts of vitamin C have shown either no change or a decreased risk of kidney stone formation.42,43,44 Nonetheless, it seems that in some individuals high vitamin C intake can lead to a rapid increase in urinary oxalate, and in one case stones developed within a few days.45 The bottom line: People with a history of kidney stones should probably limit vitamin C supplements to about 100 mg daily.46
There is also a controversy about calcium. In the past, doctors frequently advised people with a history of calcium oxalate stones to reduce their calcium consumption. The reasoning was obvious: Since you need calcium to make such stones, reducing calcium intake might be expected to protect against them. However, a five year study of 120 men with recurrent calcium stones found that a diet with normal calcium intake but low in animal protein and salt protected against stones better than a low calcium diet with no other changes.50 In addition, large observational studies suggest that on average higher calcium intake lowers the risk of developing calcium stones.47,48 Nonetheless, restriction of calcium intake may still be appropriate for certain people.49 Ask your physician for advice specific to you.
View References
Last reviewed March 2002 by Medical Review Board
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