Kidney Stone Prevention: 'Fact versus Fiction'

According to current estimates, kidney stones will develop in one in 10 people during their lifetime. This translates into nearly 30 million people in the United States. The prevalence is highest among those aged 30-45 years. High urinary calcium can be the cause of kidney stones in upwards of 80% of cases. The most prevalent stone composition is calcium oxalate. Once kidney stones develop, patients have a 50%-75% likelihood of developing another stone. The yearly cost of kidney stones in the United States was $2 billion (treatments, hospitalizations, lost work, etc.) in 1994 and is now estimated at $5 billion.1

Clearly, prevention is paramount when dealing with kidney stones. General guidelines for prevention include moderate protein intake, minimal salt ingestion, and drinking enough clear liquids to generate two liters of urine per day. A low oxalate diet has proved beneficial for preventing calcium oxalate stones. Reducing elevated urinary calcium levels helps to improve urinary saturation kinetics. Uric acid stones require dietary manipulation, adequate fluid intake to optimize volumes, and manipulation of urinary pH. Cystine stones, while relatively rare, require their own preventive measures.

Which fluid to drink is controversial. While water is the mainstay, a number of articles tout the benefit of different juices. For example, lemon juice increases urinary citrate and may prevent calcium stones. Whether one uses the recommended half cup of lemon juice per day straight up or diluted, is a personal choice. Lemonade is another frequently recommended choice. There are various opinions when it comes to the benefits of orange juice. It, too, increases urinary citrate levels, but there is concern that it could raise oxalate levels. Apple and cranberry juice contain oxalates and have been associated with a higher risk of calcium oxalate stones. Likewise, grapefruit juice has been associated with increased risk of stone formation. Soft drinks, via their phosphorus content, may lead to increased risk for kidney stones.2,3 The choice of fluid depends on other variables in the patient's urinary chemical composition.

What about sugar? Analysis from the Nurses Health Study II has shown that sugar increased kidney stone risk in young women by more than 30%. Whether this was an independent variable was unclear but the message is that high sugar, whether fructose or other sugar, is probably detrimental in the prevention of further kidney stones.

And the calcium controversy?  Calcium supplements, in excess, will increase your risk for forming kidney stones. Given all of the studies and commentaries, the simple take home message is that a diet containing normal amounts of calcium along with salt and animal protein reduction will likely protect against stones better than a low calcium regimen. It is accepted that a diet too low in calcium intake will allow preferential absorption of oxalate in the gut and increase the risk of calcium oxalate stones.

If diet alone is not helpful in correcting an abnormal urinary chemical environment, then medications are sometimes offered. These include thiazide diuretics for high urinary calcium levels, citrate supplementation for low urinary citrate levels, cystine binding drugs (i.e., penicillamine) for cystine stone prevention, as well as new options on the horizon, including oxalate degrading enzymes. But, like most drugs, these options have side effects. Thiazides, for instance, can worsen glucose tolerance, cause electrolyte imbalance, and aggravate triglyceride levels.