Introduction The sharp and irregular objects known as kidney 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.
Tiny stones may pass unnoticed, but 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 the urine of all humans, natural biochemistry is usually able to prevent them from crystallizing. However, sometimes these protective methods fail and a stone develops. 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. This article focuses mainly on the calcium oxalate stones.
It is not known why some people develop kidney stones and others do not. However, once a person has a stone, he or she is fairly likely to develop another.
Low fluid intake greatly increases the risk of developing virtually all types of stones. For this reason, persons 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.
High intakes of sodium and protein (particularly animal protein) may also increase the risk of calcium oxalate stones, although some studies have found that protein has no such effect. Oxalate-rich foods, such as spinach, rhubarb, and cocoa, may also increase the risk of developing calcium oxalate stones. Indirect evidence suggests that the regular use of cranberry concentrate tablets might also increase the risk of kidney stones. 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. High-calcium foods, however, do not seem to increase the risk of calcium oxalate stones.
Conventional treatment for kidney stones varies depending on symptoms and 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 stones that cause problems may be
treated with extracorporeal shock-wave lithotripsy, a technique that can break
up the 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 Natural Treatments
Citrate. Citrate, or citric acid, is an ordinary component of the human 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. Citrate also prevents tiny calcium oxalate crystals from growing and massing together into larger stones. Finally, citrate 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
U.S. Food and
Drug Administration in 1985 for the prevention of two kinds
of kidney stones: calcium stones (including calcium oxalate stones) and uric acid
stones. In a three-year double-blind study of fifty-seven 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.
Potassium-magnesium citrate was studied in a three-year trial involving sixty-four participants with a history of calcium oxalate stones. During the study, new stones formed in only 12.9 percent of those taking the potassium-magnesium citrate supplement, compared to 63.6 percent of those taking placebo. Benefits have been seen in other small studies too.
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. However, calcium citrate has not 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. Lemon juice may be preferable, as it has almost five times the citrate of orange juice. A small study found that drinking two liters of lemonade daily doubled urinary citrate in people with decreased urinary citrate. One should avoid regular consumption of grapefruit juice, however: In one large-scale study, women drinking eight ounces of grapefruit juice daily increased their risk of stones by 44 percent.
It was first thought that citrate supplements were helpful against kidney stones only in persons who did not excrete the normal amount of citrate in their urine. Some researchers now suggest that citrate treatment may also be useful for those at risk for stones whose citrate excretion is normal. 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 percent of people who take it. Potassium-magnesium citrate may potentially cause the same problem, although one study found it to be no more irritating than placebo.
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. In addition, the urinary antiseptic methenamine is less effective in alkaline urine. Conversely, the blood levels of other drugs could increase, possibly increasing the risk of toxicity. These drugs include stimulants, such as ephedrine and methamphetamine, and the drugs flecainide and mecamylamine.
Other Proposed Natural Treatments 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 tube and decreases stone formation in rats. However, human studies on magnesium have shown mixed results. In one two-year open study, 56 persons taking magnesium hydroxide had fewer recurrences of kidney stones than 34 persons not given magnesium. In contrast, a double-blind (hence, far more reliable) study with 124 people found that magnesium hydroxide was essentially no more effective than placebo.
Two studies performed in Thailand hint that pumpkin seeds might help to prevent kidney stones among children at high risk for developing them. However, this research looked only at chemical changes in the urine suggestive of a possible preventive effect, not at actual reduction of stones. Furthermore, the design of the studies did not reach modern standards.
The herb rose
hips might also improve the chemical composition of urine and
thereby reduce kidney stone risk. However, rose hips are very high in vitamin C,
and vitamin C itself has shown potential risks in people with a tendency toward
stones.
Vitamin
B6
might help prevent calcium oxalate stones in
certain persons. Deficiencies in this vitamin increase the amount of oxalate in
the urine of animals and humans, and a small uncontrolled study found that
supplementation decreased oxalate excretion in people with a history of stones. In
addition, a fourteen-year observational study of more than 85,000 women with no
history of kidney stones found that women with high intakes of vitamin
B6 developed fewer stones than those with the lowest intake. A
large-scale observational study of more than 45,000 men found no link between
vitamin B6 and stones. (Observational studies are notorious for
producing misleading results. Only double-blind trials can provide evidence of
benefit.) Several supplements, including fish oil, gamma-linolenic acid,
glycosaminoglycans, and vitamin A and aloe, are also sometimes recommended for
kidney stones, but there is only scant preliminary evidence to suggest that they
are helpful.
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 herbs include asparagus, birch leaf, bishop’s weed fruit, buchu, cleavers, couch grass, dandelion, goldenrod, juniper, rosemary, horsetail, java, lovage, parsley, petasites, shiny restharrow, and stinging nettle herb and root combinations. However, there is no meaningful evidence that they are 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. However, because the study lacked a placebo group, the results are unreliable.
Herbs and Supplements to Use with Caution According to some research, the use of vitamin C
supplements can slightly raise levels of oxalate in the urine, which could, in
turn, increase the 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. 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. People
with a history of kidney stones should probably limit vitamin C supplements to
about 100 milligrams daily.
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 the use of calcium supplements may slightly increase kidney stone risk.
Increased intake of calcium from food, however, does not seem to be associated
with increased risk of kidney stones and could even help prevent them. Therefore,
persons with a history of kidney stones might be best advised to get their calcium
from food rather than from supplements. Alternatively, one study suggests that if
calcium supplements are taken with food, no harm results. Furthermore, the use of
calcium as calcium citrate may present no increased risk, presumably because the
citrate portion of the supplement has activity against kidney stones.
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. Also, regular consumption of grapefruit juice may significantly increase the risk of stones.
Bibliography
Allie-Hamdulay, S., and A. L. Rodgers. “Prophylactic and Therapeutic Properties of a Sodium Citrate Preparation in the Management of Calcium Oxalate Urolithiasis.” Urological Research 33 (2005): 116-124.
Curhan, G. C., et al. “Beverage Use and Risk for Kidney Stones in Women.” Annals of Internal Medicine 128 (1998): 534-540.
Heller, H. J., et al. “Effect of Dietary Calcium on Stone Forming Propensity.” Journal of Urology 169 (2003): 470-4.
Kirdpon, S., et al. “Changes in Urinary Compositions Among Children After Consuming Prepared Oral Doses of Aloe (Aloe vera Linn.).” Journal of the Medical Association of Thailand 89 (2006): 1199-1205.
Rodgers, A. “Effect of Cola Consumption on Urinary Biochemical and Physicochemical Risk Factors Associated with Calcium Oxalate Urolithiasis.” Urological Research 27 (1999): 77-81.
Sakhaee, K., et al. “Stone Forming Risk of Calcium Citrate Supplementation in Healthy Postmenopausal Women.” Journal of Urology 172 (2004): 958-961.
Traxer, O., et al. “Effect of Ascorbic Acid Consumption on Urinary Stone Risk Factors.” Journal of Urology 170 (2003): 397-401.
