Kidney stones are solid deposits of minerals and salts that have crystallized together in the kidneys.
Usually, the fluid in urine prevents waste products from coming into contact with each other. Kidney stones begin to form when there is not enough fluid or too much solid waste content in the urine.
Though most kidney stones develop in the kidneys, they can form anywhere in the urinary tract.
According to the National Kidney Foundation, 1 in 10 people in the United States develop a kidney stone during their lifetime. The risk of kidney stones is 19 percent for men and 9 percent for women.
Most men experience their first kidney stone after the age of 30.
Researchers still are not exactly sure how and why kidney stones occur, although they are one of the oldest medical conditions known to affect humans.
Dehydration is considered the largest risk factor for kidney stones. However, certain foods and various lifestyle habits can increase the risk of developing stones.
People who suspect they have kidney stones or are at a high risk of developing them should consult a doctor to find out what type of kidney stone they have and determine which specific foods or activities to avoid.
There are many things a person can do to help prevent kidney stones, including:
1. Staying hydrated
When urine contains more fluid, it is less likely that minerals and salts will clump together and begin to form stones. Darker urine is a sign of dehydration. Ideally, urine should appear faint yellow.
For many people, the recommended 8 glasses of water per day are not enough. To decrease the risk of kidney stones, a person can try drinking at least 12 glasses of fluid daily.
At least half of a person's fluid intake should be pure water. Caffeinated, carbonated, and sweetened drinks can all increase the risk of stones.
2. Reducing salt intake
Sodium, or salt, can cause water retention and lead to dehydration. Adults should aim to keep their salt intake below 2300 milligrams (mg) daily or the equivalent of one teaspoon of table salt.
Examples of high-salt foods include:
- deli or smoked meats
- most packaged or prepared meals
- potato chips
- most canned soups
- most ready-to-make noodle or side dishes
- foods that contain other types of sodium, including sodium bicarbonate, disodium phosphate, monosodium glutamate, baking powder, nitrites, and sodium nitrate
3. Maintaining a healthy body weight
Being overweight can put stress on the kidneys; however, it is important to lose weight safely. Crash-dieting, low-carb diets, and high animal-based-protein diets can all increase the risk of kidney stones.
4. Limiting foods with calcium oxalate
Kidney stones can consist of many different compounds, including uric acid, struvite, and cysteine. The most common type of kidney stone involves calcium oxalate. A 2014 study examining nearly 50,000 kidney stones found that 67 percent of stones were comprised predominately of calcium oxalate.
Restricting oxalate intake is usually only recommended for those at a high risk of kidney stones or those with high oxalate levels.
Consuming calcium with oxalate-rich foods may reduce the risk of stones by binding the chemicals before they reach the kidneys.
Foods that are rich in oxalate include:
- grapefruit and cranberry juice
- some nuts, including cashews and peanuts
- most berries
- celery and parsley
- whole grains
5. Reducing alcohol intake
Alcohol causes cells to increase fluid output while preventing fluid absorption, leading to dehydration.
6. Avoiding excessive caffeine consumption
It is important to remember that certain sodas, chocolate, teas, and energy drinks contain caffeine.
7. Avoiding sugary drinks
Sweetened drinks, especially those containing high-fructose corn syrup, have been linked to an increased risk of kidney stones.
8. Getting enough dietary calcium
While calcium oxalate is the most common compound in kidney stones, some of the calcium found in food actually helps reduce the risk of stones.
Most dairy products are a good source of calcium. Many other foods are fortified with calcium, including:
- orange juice
- canned fish with bones, such as sardines
- some cereals
9. Increasing citric acidic intake
About 60 percent of individuals with kidney stones also have hypocitraturia or low citric acid levels.
Good sources of citric acid include:
- one 4-ounce glass of undiluted, unsweetened lemon or lime juice
- one 8-ounce glass of orange juice
- one 8-ounce glass of melon or mango juice
10. Monitoring the intake of high-acid foods
Highly acidic urine can increase the risk of kidney stones and make passing the stones more painful.
High amounts of acid in the urine also encourage the kidneys to reabsorb, rather than excrete, citrate. Citrate is a compound shown to help flush out calcium-based stones and impair their growth.
Foods that are high in acid include:
- red meat and pork
- most types of fish
- most cheeses
High-acid foods do not need to be avoided entirely, as they can be a good source of protein. However, a person should monitor and limit their intake of these foods if they are experiencing frequent kidney stones.
11. Taking supplements and vitamins
A wide range of natural supplements and vitamins may help reduce the risk of kidney stones, including:
Small kidney stones may not cause any symptoms and sometimes pass on their own without much discomfort. Medium to large kidney stones can cause intense, sharp pain.
Symptoms usually begin once the stones have started to travel through the urinary system. Stones that become stuck can cause a back up of urine, which can be extremely painful.
Common symptoms of kidney stones include:
- intense, non-stop pain in the lower back
- bloody urine
- vomiting or nausea, often from the intense pain
- fever and chills
- very unpleasant or odd smelling urine
- cloudy urine
- aching stomach pain that does not improve with gas medication
Anytime a person suspects that a kidney stone is the cause of substantial pain or discomfort, it is important to see a doctor.
Although most people experience no long-term consequences from kidney stones, they can be extremely painful and require medical monitoring.
In most cases, treating kidney stones involves increasing fluid intake, taking pain medications, and taking medications that make urine less acidic.
In minor cases, individuals may be allowed to go home and wait for the stone or stones to pass. In more serious cases, hospitalization may be required.
Stones that are too large to be passed or become stuck in the urinary tract may require surgery. Surgery to remove the stones may also be necessary if an infection has developed around it.