Many factors can contribute to your chance of having a kidney stone, including diet and fluid intake, where you live, or even your work environment.
Kidney stones typically form when your urine becomes too concentrated, causing crystals to build up inside the kidneys. Crystals begin to stick together and gradually build up into a rock-like mass. Initially, kidney stones are quite small in size, but over time, as more and more crystals attach, they can grow quite large.
The crystals that form kidney stones are made from substances normally present in the urine. These substances include calcium, oxalate, phosphate, uric acid and other chemicals. Our kidneys normally excrete these chemicals into the urine. However, when their concentration in the urine is very high, these chemicals don’t stay dissolved, and instead, begin to “crystallize out” of the urine. There are other substances in the urine, called “inhibitors”, which help to keep the crystals from sticking together. When the concentration of crystals is too high, or the relative amount of inhibitors is too low, a kidney stone will form.
Many factors can contribute to your chance of having a kidney stone, including:
- Family history
- Diet and fluid intake
- Where you live
- Even your work environment
There are several different types of kidney stones, each with a different chemical composition. The vast majority of kidney stones contain calcium. Calcium stones are composed of calcium that is chemically bound to either oxalate (calcium oxalate stones) or phosphate (calcium phosphate stones). Of these, calcium oxalate is far more common. Pure calcium phosphate stones are rare, and usually indicate an underlying illness or metabolic disorder. The most common stone composition is actually a mixture of mostly calcium oxalate with a little bit of calcium phosphate.
About 15% of kidney stones contain no calcium. These include uric acid stones, struvite stones and cystine stones.
In the United States, about 1 person in 10 will develop a kidney stone during their lifetime. Last year, kidney stones were responsible for over 600,000 emergency room visits in the United States. We know that men are more likely to have kidney stones than women. Caucasians are 5 times more likely to have kidney stones than African-Americans. The peak incidence is between 40 and 50 years of age, and appears to decline after that.
Kidney stones tend to recur. If a man has had one kidney stone, and does nothing to reduce his risk of recurrence, studies show he has about a 60 to 70% chance of having another. If a man has had two kidney stones, the chances of recurrence go up to over 90%. The odds of recurrence are slightly lower for women.
There are steps you can take to reduce your risk of kidney stones. The first step in prevention is to understand which chemical type of kidney stone you are making. So, it is very important to send your stone or stone fragment to the lab for analysis. If you are trying to pass a kidney stone you should strain your urine. Catch any stone or gravel that appears, and bring it to your urologist’s office. If you have had your stone removed with an extraction procedure, your urologist will send it to the lab for analysis. Finally, patients who undergo shockwave lithotripsy – a procedure which break the stone up with sound waves – should carefully strain their urine in the days (and possibly weeks) after the procedure, and bring to their urologists any fragments or gravel that appears.
Depending on the chemical composition of your stone, and the number of stones you’ve had in the past, your doctor may suggest that you undergo specialized lab tests. These tests are designed to measure the amount of certain chemicals in your blood and urine, and detect the specific imbalance or excess which might be causing stones to form. The results of these lab tests may indicate the need for daily use of a prescription medication to reduce the risk of stone recurrence.
Diet, Lifestyle and Behavior Changes
Dilution Is the Best Solution
The single most effective step to prevent recurrence is to increase your fluid intake. By drinking a total of 8 to 10 glasses of fluid per day, you will dramatically dilute your urine, making it less concentrated. This will keep crystals from forming, and reduce the likelihood of stone formation. At least half of the fluid intake should be water.
If you have trouble determining your fluid status, pay attention to your urine. Dark urine usually means that you are not getting enough fluid. The goal is to drink enough so that your urine is pale in color.
Reduce Your Protein Intake
Studies have shown that increased protein intake (i.e., meat, eggs, cheese, etc.) will lead to higher levels of calcium, uric acid and oxalate in the urine – all of which can increase the risk of calcium stone formation. “Low-carb” diets, which are generally high in protein and fat, are NOT recommended for individuals with a history of calcium kidney stones. To reduce your risk of calcium stone formation, reduce your intake of animal protein, and, instead, substitute plant protein sources such as legumes, nuts and seeds, and whole grains.
Reduce Your Sodium Intake
Studies have consistently shown that higher sodium intakes lead to increased calcium in the urine. Many experts believe that restricting sodium to no more than 2000 mg per day while increasing fluid intake is one of the most effective means of reducing calcium stone recurrence. Remember, however, that high levels of sodium are found in many prepared foods, and not just in the salt shaker. Whenever possible, reduce your intake of canned or processed foods, look for “reduced sodium” products, and avoid adding extra salt to your food.
Moderate Calcium Intake
Contrary to earlier beliefs, dietary calcium – meaning calcium we get from food – is actually not a problem for calcium kidney stone formers. In fact, there is evidence that moderate intake of calcium-containing foods actually protects against stone formation by binding dietary oxalate, and preventing its absorption. So, do NOT eliminate calcium containing foods from your diet unless your health care provider advises it.
Calcium supplements, on the other hand, may increase your risk of stone formation. You should discuss this possibility with your health care provider before taking any calcium supplement.
Watch Your Oxalate Intake
Your urologist may recommend that you reduce or eliminate your intake of oxalate-rich foods. Foods which are particularly high in oxalate-rich foods. Foods which are particularly high in oxalate content include chocolate or cocoa, spinach (and other dark, leafy greens), beets, strawberries, wheat germ, peanuts, pecans, cola, tea and soy.
Avoid High-Dose Vitamin C Supplements
High-dose vitamin C (ascorbic acid) supplements should be avoided unless otherwise recommended by your health care provider. Generally, the amount of vitamin C found in a multivitamin is safe, but higher amounts of vitamin C from supplements may increase the risk of kidney stone recurrence in those at an increased risk.
Increase Your Intake of “Stone Inhibitors”
Several substances found in the urine have been clearly shown to reduce the formation of calcium based kidney stones. Two of the most important are citrate and magnesium.
Lemon juice has been found to increase the level of citrate in the urine. Real lemonade (not from a powder mix) is an excellent way to increase both your citrate and fluid intake.
Nutritional supplements containing magnesium, potassium and citrate may also help to increase the concentration of “stone inhibitors” in the urine. Ask your urologist before starting any regimen of nutritional supplementation.