“Doctor, What Causes Kidney Stones?”
By David L. Casey, MD

Printable version

 
This is perhaps the most frequent question I’m asked from day to day.  Instead of repeating the same explanation to everyone day in and day out, I decided to print out some general information on stones and also provide some generic recommendations for prevention to help patients understand kidney stones and their treatment a bit better.

First off, one has to realize that kidney stones are quite common in human beings.  They tend to run in families, and tend to be more common in hot climates such as where we live.  Although it is likely impossible to absolutely prevent stones in everyone, one can certainly reduce his or her risk of stone formation with some simple maneuvers.  Certain behaviors (poor water intake) and other dietary factors can raise the risk of stone formation, and certain foods, in individuals at risk, may also create a situation that leads to stone formation.  I will discuss these foods, and other things later in this paper.

Kidney stones are typically composed of calcium oxalate or other calcium salts, although some stones are composed of other materials, the second most common being uric acid.  Very unusual stones such as cystine may indicate a genetic problem, and “triple phosphate” or struvite stones may indicate a prior or ongoing infection with certain types of bacteria in the urine.  If a stone passes, please submit it for analysis.  This is usually done simply to rule out an “unusual” stone, but realize if it is a simple calcium oxalate stone, that really doesn’t tell us a whole lot about how to prevent future stones.

By and large, the chief “problem” with people who form stones is lack of adequate water (fluid) intake.  The calcium and other salts are simply in too high a concentration in the urine relative to water and thus will crystallize out, forming first small particles, then larger aggregates that eventually coalesce to form stones.  To help prevent this, the chief goal is to drink enough fluids to keep these materials dissolved in the dilute urine thus created.   I’m often asked, “How much water should I drink?”  The right question is actually, “How much urine should I produce?”  The answer to the latter question is at least 2 liters of urine per day (which is actually quite a lot).  A good rule of thumb is that the urine (except for perhaps the first void in the morning) should be clear like water (not yellow) when it is dilute enough.  This is, I will reiterate, by far the most important factor in stone prevention.

Other generic recommendation for stone-formers is to reduce red meat protein in the diet.  This is due to the fact that these contribute to uric acid and oxalate production in the urine, and reducing red meats can reduce risk.  This is especially true for those patients who form uric acid stones. Reduction of oxalates in the diet has been recommended, but I find this sometimes hard to always do, not always knowing specifically what food that entails.  Oxalates are high in colas (soda pops), teas, chocolate, and peanuts, and may be produced if one takes too much Vitamin C.  Therefore it probably doesn’t hurt to back off on these foods, and also I believe one tends to lessen water intake when they’re drinking soda pops as the sweetness/sugar content tends to reduce the volume of intake.  Reduction of sodium or salt in the diet has also been recommended to stone formers.  The kidney handles excess salt in a manner to increase calcium excretion, so this recommendation should be followed where feasible.  Remember this doesn’t just mean salt in the saltshaker, but also includes salty processed foods, and high salt drinks (Gatorade) and other high-sodium foods (you’ll just have to check the Nutrition Facts section on the food container!)

Reduction of calcium in the diet has long been touted as something all stone formers should do.  In fact, a brochure in our office that you may have received states this in the Prevention section on page 14.  I believe that limiting calcium to the extreme without knowing more specifics about your particular system can be counter-productive, and recent studies have suggested this to be true.  That’s not to say that massive calcium/dairy intake is advisable for stone formers, but strict adherence to a calcium free diet may NOT be in your better interest without knowing more about your blood and urine chemistries.  Therefore, unless you’ve been specifically told, do NOT avoid dairy or calcium containing foods if you’re a stone former.  However, if you’re drinking a gallon of milk, chewing 30 Tums, and then eating a quart of Blue Bell each evening, you may be overdoing it!

To summarize the 3 main points of stone prevention:

•  Increase fluid intake so as to make >2 liters of urine per day.
• Decrease red meat proteins and oxalates in the diet.
• Diminish sodium (salt) in the diet.

These generic recommendations are often enough for most folks to reduce their stone risk.  If, however, you continue to form stones, or have other reason for a “work up”, then you may be referred to a nephrologist or other specialist to get a 24-hour urine collection as well as blood work to look for a metabolic abnormality.  (*Please note that Dr. Admire often does his own metabolic workups, rather than referring patients to a nephrologist.)  These abnormalities may require a strict diet, medication, or even more aggressive treatment if something unusual is detected.  However, in many cases, even after the metabolic workup, the recommendations still come back to increase fluid intake and follow the generic dietary recommendations.

I hope this helps and I also hope you never have another stone!  Our website bookstore, listed below, has several good selections in its “Bookstore” if you want to learn more!

Best of luck,

David L. Casey, MD
Denton Urology
http://www.dentonurology.com/bookstore.html
 
 

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