Once you have had a kidney stone, you must expect it to form again. To prevent this, it is usually sufficient to drink a lot and change your diet. For people who still get kidney stones again and again, there are medicines for prevention.
About 30 to 50 out of 100 people who had a kidney stone must expect a second stone within five years. About 10 out of 100 people develop kidney stones more frequently. For many of those affected, the question, therefore, arises as to how they can prevent new stones.
Since kidney stones can have many causes, it is first important to know the chemical composition of the stones. Certain values in blood and urine also indicate the causes. About 80 percent of all kidney stones are calcium stones. Uric acid stones are responsible for about 5 to 10 percent of all kidney stones. The remaining stones consist of struvite, cystine or other rare substances.
In order to reduce the risk of kidney stones, it is usually sufficient to drink enough and, if necessary, to adjust the diet. For people with a high risk of kidney stones, medication may be useful to protect them from other stones.
Does it help to drink much?
Kidney stones develop when the calcium or uric acid salts in the urine can no longer dissolve. This can happen if their concentration is too high. The salts then form crystals that become stones. This risk is lower if the urine is as diluted as possible.
One study suggests that the risk of a second kidney stone can be reduced by drinking more than normal: The participants in the study drank so much that they excreted about 2.5 liters of urine a day. Over a period of five years:
27 out of 100 people who drank as much as before had a second kidney stone.
12 out of 100 people who drank more fluids had a second kidney stone.
The increased amount of fluid could thus save 15 out of 100 people from another kidney stone. The study participants were able to cope well with the fact that they drank more than before.
Soft drinks should be avoided
Many soft drinks like cola contain phosphoric acid (the food additive E338). It may promote the formation of kidney stones. There is only one conclusive study on the question of whether the absence of soft drinks also reduces the risk of further kidney stones. A good 500 men were encouraged to drink fewer soft drinks.
On average, they reduced their consumption to less than 100 milliliters a day – that is less than half a glass. Compared to a group of men who did not change their drinking preferences, their risk of kidney stones decreased. Over the course of three years:
41 out of 100 men who drank as many soft drinks as before had another kidney stone.
34 out of 100 men who drank fewer soft drinks had another kidney stone.
This means that 7 out of 100 men were able to protect themselves from a relapse if they consumed fewer soft drinks. Some men ended their participation in the study prematurely – possibly because they found the change difficult.
Does it make sense to change your diet?
A diet low in calcium tends to be harmful
Calcium stones often consist of calcium and oxalate (calcium oxalate). Both substances are found in many foods. Avoiding oxalate-containing foods such as rhubarb, parsley, walnuts, spinach or chocolate is considered helpful. However, not eating calcium-rich foods such as milk, cheese or yogurt is not a good idea. Studies show that a low-calcium diet favours kidney stones: If there is too little calcium in the food, more oxalate gets into the urine.
The situation is different if calcium is taken as a dietary supplement. Studies have shown that this promotes kidney stones – at least in menopausal women.
Comprehensive change in diet could help
The most meaningful study to date on diet and kidney stones involved men whose blood contained high levels of calcium. They were encouraged to do so as part of a major dietary change,
to drink a lot,
Avoid oxalate-rich foods such as walnuts, spinach, and chocolate,
eat little animal protein such as meat and eggs,
to eat low-salt food and
to consume sufficiently but not too much calcium, for example in the form of milk, cheese or yogurt (about 1000 to 1200 milligrams per day).
The men in the comparison group should only drink a lot and eat low oxalate and low calcium.
The results of the study showed that a comprehensive change in diet could reduce the risk of kidney stones:
Without a change in diet, 38 out of 100 men had another kidney stone within five years.
With a change in diet, 20 out of 100 men had another kidney stone within five years.
18 out of 100 men, therefore, benefited from the change in diet to avoid another kidney stone.
In some cases, a diet rich in fibre is also recommended. However, there is no scientific evidence for a preventive effect.
Influence of low-purine diet unclear
Especially people with gout and diabetes have uric acid stones. Uric acid is a degradation product of so-called purines: They are mainly formed in the body but are also partly absorbed through food. For the prevention of uric acid stones, a low-purine diet with little fish, meat and seafood is therefore recommended.
So far, however, there have been no scientific studies that have investigated whether a low-purine diet reduces the risk of uric acid stones.
When can drugs be used to prevent kidney stones?
Preventive medication may be considered if there is a high risk of further kidney stones. A high risk, for example, is the term used:
if the kidney stones already occur in childhood or adolescence.
in the case of a family predisposition to kidney stones.
certain diseases of the kidneys, urinary tract or gastrointestinal tract.
in cases of parathyroid hyperfunction.
if stones are caused by a urinary tract infection.
uric acid stones.
Cyst stones (caused by a rare inherited metabolic disorder).
Which drugs are used to prevent kidney stones depends on the type of stones:
Citrate: It combines with calcium dissolved in urine to prevent calcium crystals from forming. Citrate is available on the market as an effervescent tablet, capsule, and powder. It is used for the prevention of calcium, uric acid and cyst stones.
Thiazide diuretics: These drugs cause less calcium to enter the urine from the blood. They are among the dehydrating drugs and prevent calcium stones.
Allopurinol: This active ingredient inhibits the degradation of purines to uric acid and thus lowers the uric acid level in the urine. Allopurinol is mainly used to prevent uric acid stones.
further medicines: For the prevention of stones, which are caused by urinary tract infections, one uses means, which make the urine more acidic.
Food supplements containing magnesium increase the magnesium content in the urine. There magnesium oxalate binds and is said to inhibit the formation of calcium oxalate stones.
Using blood and urine tests and the analysis of kidney stones, doctors can assess which medications are appropriate.
Drugs for the prevention of kidney stones are permanently taken on a daily basis. As a rule, they are only considered if someone has already had kidney stones at least twice.
How effective are medicines for the prevention of kidney stones?
Studies show that the frequently used drugs used to prevent kidney stones can protect against further kidney stones. Calcium stones are the most common, and most studies have also involved people with calcium stones.
In several studies, citrate was able to protect against kidney stones:
Without citrate, 44 out of 100 people had another kidney stone within two years.
With citrate, 11 out of 100 people had another kidney stone within two years.
The agent thus saved 33 out of 100 people from another stone.
Possible side effects of citrate are stomach intestine complaints and diarrhea. In the studies, about 12 out of 100 people ended the treatment because of side effects.
Studies have also shown that thiazide diuretics reduce the risk of kidney stones:
Without thiazide diuretics, 47 out of 100 people had another kidney stone within three years.
With thiazide diuretics, 24 out of 100 people had another kidney stone within three years.
The intake of thiazide diuretics helped 23 out of 100 people to avoid the formation of another kidney stone.
Thiazide diuretics can have various side effects. These include low blood pressure with dizziness and fatigue, dry mouth and erectile dysfunction. In the studies, 8 out of 100 people stopped treatment due to side effects.
Allopurinol is mainly used for the prevention of uric acid stones. So far, however, its efficacy has only been investigated in studies involving people with calcium stones. There it was shown that allopurinol can protect against calcium stones:
Without allopurinol, 55 out of 100 people had another kidney stone within three and a half years.
With allopurinol, 33 out of 100 people had another kidney stone within three and a half years.
The drug thus protected 22 out of 100 people from another stone.
Allopurinol can cause skin rashes and sometimes a gout attack. In the studies, however, no more people discontinued treatment with allopurinol because of side effects than participants who did not take the drug.
Other drugs for the prevention of certain stone types, such as magnesium or L-methionine, have not been well studied so far. It is therefore unclear whether they protect against kidney stones.