Kidney stones are deposits of minerals and salts that crystallize in the kidneys. They become solid, and passing them in the urine can be extremely painful.
Usually, the fluid in urine prevents waste products from coming into contact with each other. However, kidney stones can 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.
Researchers are still not exactly sure how or why kidney stones develop.
Dehydration is the primary risk factor for kidney stones. However, certain foods and various lifestyle habits can also increase the risk of developing them.
People who suspect that they have kidney stones or are at 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 steps a person can take to reduce the risk of kidney stones, including:
1. Staying hydrated
When urine contains more fluid, it is less likely that minerals and salts will cluster together and form stones. Darker urine is a sign of dehydration. Ideally, urine should appear pale yellow.
Doctors tend to recommend that a person drinks between six and eight 8 ounce (oz) glasses of water per day.
2. Reducing salt intake
Sodium, or salt, can cause water retention and lead to dehydration. The Food and Drug Administration (FDA) suggest that adults aim to keep their salt intake below 2,300 milligrams(mg) daily. This is equivalent to around one teaspoon of table salt.
Some 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
Having overweight or obesity can put stress on the kidneys. However, it is always important to lose weight gradually and safely.
Crash dieting and following a diet high in animal protein can both 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.
One 2014 study examined nearly 44,000 kidney stones and found that 67% were composed predominately of calcium oxalate.
Doctors usually only recommend restricting oxalate intake to those at a high risk of kidney stones or those with high oxalate levels.
Consuming calcium alongside oxalate-rich foods may reduce the risk of kidney stones by binding the chemicals together before they reach the kidneys.
Foods that contain high levels of oxalate include:
- grapefruit and cranberry juice
- some nuts, including cashews and peanuts
- most berries
- celery and parsley
- whole grains
5. Avoiding excessive caffeine consumption
Caffeine speeds up metabolism and can cause dehydration. The recommended upper limit for adults is 400 mg of caffeine daily, which is equivalent to about four cups of coffee. It is important to remember that certain sodas, chocolate, teas, and energy drinks can also contain caffeine.
6. Avoiding sugary drinks
Some studies have linked sweetened drinks, especially those containing high-fructose corn syrup, to the development of kidney stones.
At least half of a person’s fluid intake should be pure water. Some research suggests that caffeinated drinks can increase the risk of stones, as can sweetened drinks and sodas.
7. Getting enough dietary calcium
Although calcium oxalate is the most common compound in kidney stones, consuming some dietary calcium helps reduce the risk of stones.
Most dairy products are a good source of calcium. Manufacturers fortify many other foods with calcium, including:
- orange juice
- canned fish with bones, such as sardines
- some cereals
8. Increasing citric acidic intake
About 60% of people with kidney stones also have low citric acid levels.
Some good sources of citric acid include:
- one 4 oz glass of undiluted, unsweetened lemon or lime juice
- one 8 oz glass of orange juice
- one 8 oz glass of melon or mango juice
9. Monitoring the intake of high acid foods
Highly acidic urine can increase the risk of uric acid kidney stones and make passing them more painful. High amounts of acid in the urine also encourage the kidneys to reabsorb citrate rather than excrete it. Citrate is a compound that can help flush out calcium-based stones, as well as impair their growth.
Highly acidic foods include:
- red meat and pork
- most types of fish
- most cheeses
People do not need to avoid high acid foods entirely, as they can be a good source of protein. However, a person should monitor and limit their intake of these foods if they experience frequent kidney stones.
10. Taking supplements and vitamins
A wide range of natural supplements and vitamins are available that may help reduce the risk of kidney stones in some people, including:
- potassium citrate
- vitamin B-6, which occurs in foods such as bananas, mangos, soybeans, avocados, and halibut
- other B vitamins, including riboflavin, thiamin, and B-12, none of which are harmful to people with kidney stones
- vitamin D
- fish oils
However, for many of these, it is best to check with a doctor or dietitian before use. Some supplements can increase the risk for some individuals.
How common are kidney stones?
According to the National Kidney Foundation, almost 1 in 10 people in the United States develop a kidney stone during their lifetime. The risk is around 19% for men and 9% for women.
Most men experience their first kidney stone after the age of 30 years.
Small kidney stones may not cause any symptoms, and they sometimes pass on their own without causing much discomfort. Medium-to-large kidney stones, however, 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 backup of urine. This can be extremely painful.
Common symptoms of kidney stones include:
- constant, intense pain in the lower back
- bloody urine
- vomiting or nausea, often from the pain
- fever and chills
- very unpleasant or odd-smelling urine
- cloudy urine
- stomachache that does not improve with gas medication
Treatment and when to see a doctor
If 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 using medications that make the urine less acidic.
People with smaller stones may be able to go home and wait for the stone or stones to pass. People with larger or more severe stones may need to stay in the hospital.
Stones that are too large to pass or that 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.