kamen u bubregu

Kidney Stones

Also indexed as: Nephrolithiasis, Renal Calculi, Urinary Calculi, Urolithiasis

Kidney stones are hard masses that can grow from crystals forming within the kidneys. The medical term for kidney stone formation is nephrolithiasis. The stones themselves are called renal calculi. Kidney stones often cause severe pain, sometimes accompanied by gastrointestinal symptoms, chills, fever, and blood in urine.

Most kidney stones are made of calcium oxalate. People with a history of kidney stone formation should talk with their doctor to learn what type of stones they have—approximately one stone in three is made of something other than calcium oxalate and one in five contains little if any calcium in any form.

Calcium oxalate stone formation is rare in primitive societies, suggesting that this condition is preventable.1 People who have formed a calcium oxalate stone are at high risk of forming another kidney stone.

Conventional treatment options: Pain-relief medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs—e.g., diclofenac [Voltaren®], etodolac [Lodine®]) or narcotics (e.g., hydrocodone-paracetamol [Vicodin®], paracetamol-codeine [Tylenol #3®], oxycodone-acetaminophen [Percocet®]), are commonly prescribed for an acute episode. Lithotripsy, an ultrasound treatment that breaks the stones into pieces small enough to pass in the urine, has largely replaced surgery as the preferred method for stone removal. The diuretic trichlormethiazide (Diurese®, Niazide®, Trichlorex®) is sometimes prescribed for prevention of calcium oxalate stone formation.

Caution: The information included in this section pertains to prevention of calcium oxalate kidney stone recurrence only—not to other kidney stones or to the treatment of acute disease. The term “kidney stone” as used in this section refers only to calcium oxalate stones. However, information regarding how natural substances affect urinary calcium levels may also be important for people with a history of calcium phosphate stones.

Dietary changes that may be helpful: Increasing dietary oxalate can lead to an increase in urinary oxalate excretion. Increased urinary oxalate increases the risk of stone formation. As a result, most doctors agree that kidney stone formers should reduce their intake of oxalate from food as a way to reduce urinary oxalate.2 Many foods contain oxalate; however, only a few—spinach, rhubarb, beet greens, nuts, chocolate, tea, bran, almonds, peanuts, and strawberries—appear to significantly increase urinary oxalate levels.3 4

Increased levels of urinary calcium also increases the risk of stone formation. Consumption of animal protein from meat, dairy, poultry, or fish increases urinary calcium. Perhaps for this reason, animal protein has been linked to an increased risk of forming stones5 6 and vegetarians have been reported to be at lower risk for stone formation.7 As a result, some doctors recommend reducing intake of foods containing animal protein. One isolated report paradoxically found an increase in kidney stone recurrences following the restriction of animal protein while at the same time increasing dietary fibre.8 However, other researchers find such a diet appears to reduce the risk of forming stones,9 and most researchers continue to find links between kidney stone risk and animal protein intake.10 11

Salt increases urinary calcium excretion in stone formers.12 13 14 In theory, this should increase the risk of forming a stone. As a result, some researchers have suggested that reducing dietary salt may be a useful way to decrease the chance of forming additional stones.15 16 Increasing dietary salt has also affected a variety of other risk factors in ways that suggest an increased chance of kidney stone formation.17 Doctors frequently recommend that people with a history of kidney stones reduce salt intake. To what extent such a dietary change would reduce the risk of stone recurrence remains unclear.

Potassium reduces urinary calcium excretion,18 and people who eat high amounts of dietary potassium appear to be at low risk of forming kidney stones.19 Most kidney stone research involving potassium uses the form potassium citrate, although citrate itself may lower the risk of stone recurrence. However, in some potassium research, a significant decrease in urinary calcium occurs even in the absence of added citrate.20 This outcome suggests that increasing potassium itself may reduce the risk of kidney stone recurrence. The best way to increase potassium is to eat fruits and vegetables. The level of potassium in food is much higher than the small amounts found in supplements.

Most citrate research conducted with people who have a history of kidney stones involves supplementation with potassium citrate or magnesium citrate. In one double-blind trial, recurrence of kidney stone formation dropped from 64% to 13% for those receiving high amounts of both supplements.21 In that trial, people were instructed to take six pills per day—enough potassium citrate to provide 1,600 mg of potassium and enough magnesium citrate to provide 500 mg of magnesium. Both placebo and citrate groups were also advised to restrict salt, sugar, animal protein, and foods rich in oxalate. Several similar trials have proven that potassium and magnesium citrate supplementation reduces kidney stone recurrences.22

Citric acid is found in many foods and may also protect against kidney stone formation.23 24 The best food source commonly available is citrus fruits, particularly lemons. One preliminary study found that drinking 2 liters (approximately 2 quarts) of lemonade per day improved the quality of the urine in ways that are associated with stone prevention.25 Lemonade was far more effective than orange juice. The lemonade was made by mixing 4 oz lemon juice with enough water to make 2 liters. The smallest amount of sweetener possible should be added to make the taste acceptable. Further study is necessary, however, to determine if lemonade can prevent recurrence of kidney stones.

Drinking grapefruit juice has actually been linked to an increased risk of kidney stones in two large studies.26 27 Whether grapefruit juice actually causes kidney stone recurrence or is merely associated with something else that increases risks remains unclear; some doctors suggest that people with a history of stones should restrict grapefruit juice intake until more is known.

Bran, a rich source of insoluble fibre, reduces the absorption of calcium, which in turn causes urinary calcium to fall.28 In one trial, risk of forming kidney stones was significantly reduced simply by adding one-half ounce of rice bran per day to the diet.29 Oat and wheat bran are also good sources of insoluble fibre and are available in natural food stores and supermarkets. Before supplementing with bran, people should check with a doctor because some people—even a few with kidney stones—don’t absorb enough calcium. For those people, supplementing with bran might deprive them of much-needed calcium.

People who form kidney stones have been reported to process sugar abnormally.30 Sugar has also been reported to increase urinary oxalate,31 and in some reports, urinary calcium as well.32 As a result, some doctors recommend that people who form stones avoid sugar.33 34 To what extent, if any, such a dietary change decreased the risk of stone recurrence has not been studied and remains unclear.

Drinking water increases the volume of urine. In the process, substances that form kidney stones are diluted, reducing the risk of kidney stone recurrence. For this reason, people with a history of kidney stones should drink at least two quarts per day. It is particularly important that people in hot climates increase their fluid intake to reduce their risk.35

Drinking coffee or other caffeine-containing beverages increases urinary calcium.36 Long-term caffeine consumers are reported to have an increased risk of osteoporosis,37 suggesting that the increase in urinary calcium caused by caffeine consumption may be significant. However, coffee consists mostly of water, and increasing water consumption is known to reduce the risk of forming a kidney stone. While many doctors are concerned about the possible negative effects of caffeine consumption in people with a history of kidney stones, preliminary studies in both men38 39 and women40 have found that coffee and tea consumption is actually associated with a reduced risk of forming a kidney stone. These reports suggest that the helpful effect of consuming more water by drinking coffee or tea may compensate for the theoretically harmful effect that caffeine has in elevating urinary calcium. Therefore, the bulk of current research suggests that it is not important for kidney stone formers to avoid coffee and tea.

Similarly, some doctors have been concerned about a reported link between drinking soft drinks and risk of kidney stones41 that was followed by a study showing that men who refrained from drinking soft drinks (especially drinks containing phosphoric acid) reduced their risk of stone recurrences compared with men permitted to consume soft drinks.42 Phosphoric acid is thought to affect calcium metabolism in ways that might increase kidney stone recurrence risk. Research in this area remains somewhat inconsistent, however. In one large trial, people who consumed more soft drinks were not at increased risk.43

Nutritional supplements that may be helpful: In the past, doctors commonly recommended that people with a history of kidney stones restrict calcium intake because a higher calcium intake increases the amount of calcium in the urine. However, calcium (from supplements or food) binds to oxalate in the gut before either can be absorbed, thus interfering with the absorption of oxalate. When oxalate is not absorbed, it cannot be excreted in urine. The resulting decrease in urinary oxalate actually reduces the risk of stone formation.44 The question is, which effect of supplemental calcium is more important—the increase in urinary calcium, which should increase risk of stone recurrence, or the reduction in urinary oxalate, which should reduce the risk? According to an editorial in the New England Journal of Medicine, the oxalate binding is more important than increases in urinary calcium,45 and therefore it makes sense that for most people, calcium might reduce rather than increase the risk of kidney stone formation.

According to research published in the New England Journal of Medicine, people who eat more calcium have a lower risk of forming kidney stones than people who consume less calcium.46 Most studies have also reported that people who consume more calcium have a lower, not higher, risk of forming kidney stones.47 48

However, while dietary calcium has been linked to reduction in the risk of forming stones, calcium supplements have been associated with an increased risk in a large study of American nurses.49 The researchers who conducted this trial speculate that the difference in effects between dietary and supplemental calcium resulted from differences in timing of calcium consumption. All dietary calcium is eaten with food, and so it can then block absorption of oxalates that may be present at the same meal. In the study of American nurses, however, most supplemental calcium was consumed apart from food.50 Calcium taken without food will increase urinary calcium, thus increasing the risk of forming stones; but calcium taken without food cannot reduce the absorption of oxalate from food consumed at a different time. For this reason, these researchers speculate that calcium supplements were linked to increased risk because they were taken between meals. Thus, calcium supplements may be beneficial for many stone formers, as dietary calcium appears to be, but only if taken with meals. Taken between meals, calcium supplements may increase the risk of stone formation.

When doctors recommend calcium supplements to stone formers, they usually suggest 800 mg per day in the form of calcium citrate, taken with meals. Citrate helps reduce the risk of forming a stone (see Dietary section for more information).51 Calcium citrate has been shown to increase urinary citrate in stone formers, which should act as protection against any increase in urinary calcium.52

Despite the fact that calcium supplementation taken with meals may be helpful for some, people with a history of kidney stone formation should not take calcium supplements without the supervision of a healthcare professional. Although the increase in urinary calcium caused by calcium supplements can be mild or even temporary,53 some stone formers show a potentially dangerous increase in urinary calcium following calcium supplementation; this may, in turn, increase the risk of stone formation.54 People who are “hyperabsorbers” of calcium should not take supplemental calcium until more is known. Using a protocol established years ago in the Journal of Urology, 24-hour urinary calcium studies conducted both with and without calcium supplementation determine which stone formers are calcium “hyperabsorbers.”55 Any healthcare practitioner can order this simple test.

Increased blood levels of activated vitamin D are found in some kidney stone formers, according to some,56 but not all, research.57 Until more is known, kidney stone formers should avoid taking vitamin D supplements without consulting a doctor.58

Both magnesium and vitamin B6 are used by the body to convert oxalate into other substances. Vitamin B6 deficiency leads to an increase in kidney stones as a result of elevated urinary oxalate.59 Vitamin B6 is also known to reduce elevated urinary oxalate in some stone formers who are not necessarily B6 deficient.60 61

Years ago, the Merck Manual recommended 100–200 mg of vitamin B6 and 200 mg of magnesium per day for some kidney stone formers with elevated urinary oxalate.62 Most studies have shown that supplementing with magnesium63 64 65 and/or vitamin B666 67 significantly lowers the risk of forming kidney stones. Results have varied from only a slight reduction in recurrences68 to a greater than 90% decrease in recurrences.69

Optimal supplemental levels of vitamin B6 and magnesium remain unknown. Many doctors advise 200–400 mg per day of magnesium. While the effective intake of vitamin B6 appears to be as low as 10–50 mg per day, certain people with elevated urinary oxalate may require much higher amounts, and therefore require medical supervision. In some cases, as much as 1,000 mg of vitamin B6 per day (a potentially toxic level) has been used successfully.70

Doctors who do advocate use of magnesium for people with a history of stone formation generally suggest the use of magnesium citrate because citrate itself reduces kidney stone recurrences. As with calcium supplementation, it appears important to take magnesium with meals in order for it to reduce kidney stone risks by lowering urinary oxalate.71

It has been suggested that people who form kidney stones should avoid vitamin C supplements, because vitamin C can convert into oxalate and increase urinary oxalate.72 73 Initially, these concerns were questioned because the vitamin C had been converting to oxalate after urine had left the body.74 75 However, newer studies, using methodology that rules out this potential laboratory error, have shown that as little as 1 gram of vitamin C per day can increase urinary oxalate levels in some people, even those without a history of kidney stones.76 77 In one case report, a young man who ingested 8 grams per day of vitamin C had a dramatic increase in urinary oxalate excretion, resulting in calcium-oxalate crystal formation and blood in the urine.78 On the other hand, in preliminary studies performed on large populations, high intake of vitamin C had no effect on kidney stone risk in women,79 and was associated with a reduced risk in men80 This research suggests that routine restriction of vitamin C to prevent stone formation is unwarranted. However, until more is known, people with kidney stones or a past history of stone formation should not take large amounts (greater than 1 gram per day) of supplemental vitamin C without medical supervision. Amounts significantly lower (100–200 mg per day) appear to be safe.

Glucosamine sulphate and chondroitin sulphate may play a role in reducing the risk of kidney stone formation. One study found 60 mg per day of such supplements significantly lowered urinary oxalate levels in stone formers.81 Such a decrease should reduce the risk of stone formation.

Consumption of IP-6 (inositol hexaphosphate; phytic acid) appears to reduce the potential of urine to produce calcium stones.82 IP-6 has been used historically to treat kidney stones.83 IP-6 has been tested for this purpose because of its ability to decrease calcium in the urine, theoretically decreasing the risk of developing calcium oxalate stones. In a group of 36 calcium oxalate stone-formers, 120 mg per day of IP-6 for 15 days significantly reduced the formation of calcium oxalate crystals in the urine.84 Intervention trials, assessing new stone formation as the endpoint, are needed to confirm the clinical efficacy of IP-6 in preventing kidney stones.

Are there any side effects or interactions? Refer to the individual supplement for information about any side effects or interactions.

Herbs that may be helpful: Two studies in Thailand have found that eating pumpkin seeds as a snack can help prevent the most common type of kidney stone.85 86 Pumpkin seeds appear to both reduce levels of substances that promote stone formation in the urine and increase levels of substances that inhibit stone formation. The active constituents of pumpkin seeds responsible for this action have not been identified. Approximately 5–10 grams per day of pumpkin seeds may be needed for kidney stone prevention.87

Practitioners of botanical medicine use several herbs to help facilitate passage of small kidney stones and to help prevent their formation. The efficacy of these herbs has not been documented scientifically for people with kidney stones. Because the risks associated with acute kidney stones are high, it is essential to consult with a trained practitioner before attempting to use any herb to help pass kidney stones.

The German government has approved a number of herbs that increase urine volume (herbal diuretics) as a way to help prevent kidney stone formation.88 These herbs include asparagus, birch, couch grass, goldenrod, horsetail, Java tea (Orthosiphon stamineus), lovage, parsley, spiny restharrow, and nettle. Generally they are given as teas to further increase water intake as well as deliver the medicinal herbs.

Are there any side effects or interactions? Refer to the individual herb for information about any side effects or interactions.

Checklist for Calcium Oxalate Kidney Stones

Ranking Nutritional Supplements Herbs
Primary Vitamin B6 (in the presence of elevated urinary oxalate)
Magnesium citrate and Potassium citrate (in combination)

Secondary Vitamin B6 (in the absence of elevated urinary oxalate)
IP-6
Pumpkin seeds
Other Calcium
Chondroitin sulphate

Fibre

Glucosamine sulphate

Lemonade
Asparagus
Birch leaf

Couch grass

Goldenrod

Horsetail

Java tea (Orthosiphon stamineus)

Lovage

Parsley

Spiny restharrow

Nettle

Within Healthnotes Online, information about the effects of a particular supplement or herb on a particular condition has been qualified in terms of the methodology or source of supporting data (for example: clinical, double blind, meta-analysis, or traditional use). For the convenience of the reader, the information in the table listing the supplements for particular conditions is also categorized. The criteria for the categorizations are: “Primary” indicates there are reliable and relatively consistent scientific data showing a health benefit. “Secondary” indicates there are conflicting, insufficient, or only preliminary studies suggesting a health benefit or that the health benefit is minimal. “Other” indicates that an herb is primarily supported by traditional use or that the herb or supplement has little scientific support and/or minimal proven health benefit.

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References:
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