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 may have the opposite effect.4,5
High intakes of sodium
6,7 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,
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
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, 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,
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 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 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.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 daily 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
The proper dosage of citrate depends on the chemical form and should be individualized under medical supervision.
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
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
oral diabetes drugs,
and other salicylates, and
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
and methamphetamine, as well as the drugs flecainide and mecamylamine.
, 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 tube
23 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, far more reliable) study with 124 participants found that magnesium hydroxide was essentially no more effective than placebo.30
Two studies performed in Thailand hint that
pumpkin seeds might help prevent kidney stones among children at high risk for developing them.57-58
However, this research only looked at chemical changes in the urine suggestive of a possible preventive effect, not actual reduction of stones. Furthermore, the design of the studies did not reach modern standards.
rose hips might also improve the chemical composition of urine and thereby reduce kidney stone risk.59
However, rose hips are very high in
vitamin C, and vitamin C itself has shown potential risks in people with a tendency toward stones. (See
Vitamin B6 might 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 B
6 developed fewer stones than those with the lowest intake.33
On the other hand, a large-scale observational study of more than 45,000 men found no link between B
6 and stones.34
Keep in mind that observational studies are notorious for producing misleading results. Only double-blind trials can actually provide evidence of benefit. (For information on why this is so, see
Why Does This Database Rely on Double-blind Studies?) Several supplements, including
aloe, are also sometimes recommended for kidney stones, but there is only scant preliminary evidence to suggest that they are helpful.36-39,65-66
A variety of herbs are often recommended for kidney stones, on the theory that they increase urine flow, which will help pass kidney stones. These include asparagus, birch leaf, bishop's weed fruit,
cleavers, couch grass,
horsetail, java, lovage,
parsley, petasites, shiny restharrow, and stinging nettle herb and root combinations.35
However, there is no meaningful evidence that they are really effective.
One study claimed to find trigger point injection (a form of treatment somewhat related to
acupuncture) helpful for reducing the pain of kidney stones,51
but because it lacked a
the results mean very little
According to some, but not all research, use of
vitamin C supplements can slightly raise levels of oxalate in the urine,40,41,53 which could, in turn, increase risk of kidney stones. However, large-scale observational studies have found that people who consume large amounts of vitamin C have no increased risk or even a decreased risk of kidney stone formation.42-44 Nonetheless, it seems that in certain people, 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
Calcium supplements also present concerns, because they could conceivably increase formation of calcium oxalate or other calcium-based stones. Observational studies and other forms of preliminary evidence do suggest that use of calcium supplements may slightly increase kidney stone risk.48,52,54,61
Interestingly, though, increased intake of calcium from
food does not seem to be associated with increased risk of kidney stones and could even help prevent them.47,48 Therefore, individuals with a history of kidney stones might be best advised to get their calcium from food rather than supplements. Alternatively, one study suggests that if calcium supplements are taken with food, no harm results.54 Furthermore, use of calcium as calcium citrate may present no increased risk, presumably because the citrate portion of the supplement has activity against kidney stones.55
Some evidence hints that excessive consumption of phosphorus in the form of soft drinks might increase kidney stone risk, but study results are contradictory, and if there is an effect, it appears to be small.62-64
As noted above, regular consumption of grapefruit juice may significantly increase risk of stones.17
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