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Ask Dr. Matt: Kids With Kidney Stones 

Q. My child was recently diagnosed with kidney stones. It was awful. What can we do to prevent this from ever happening again?

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A. To the surprise of many parents, children can indeed get kidney stones. Some say passing a kidney stone is worse than being shot or giving birth. I remember my dad, a seriously tough guy, passing out from pain while trying to pass a stone. Approximately 30 million Americans form kidney stones each year, more adults than children and more men than women. As in adults, there has been a rise in the frequency of stone formation in children.

To understand why, we have to consider how stones form in the first place. This leads us to the second-greatest story ever told — human mineral metabolism and supersaturation of stone-forming compounds in urine (one of my kids’ all-time favorite bedtime stories).

The story starts with calcium in the urine, as the roads to most stones are paved with calcium in the urine bound to some other nasty sidekick. Calcium is an innocent and affable organic salt, essential for normal physiologic functions, including bone formation, muscle contraction and numerous other cellular operations.

The trouble with calcium is that it is quite insecure and desperate to hook up with any other ions in its immediate vicinity. When calcium gets together with friendly compounds in the urine like citrate or magnesium, everything is OK. But when calcium hooks up with less friendly compounds like oxalate or uric acid, trouble may follow. Here’s a visual: Imagine calcium is a smiley bobble head floating around in the urine and it has to wear a hat. A citrate or magnesium hat is like a swim cap: snug fitting, smooth and sleek. A uric acid or oxalate hat is like a big Velcro cowboy hat that is prone to sticking to other Velcro cowboy hats — stones are formed by too many hats sticking together. Too many bobble heads sporting Velcro cowboy hats is bad. Fewer bobble heads wearing tidy swim caps is good.

I should emphasize that calcium in the diet is essential for many wonderful and important things in day-to-day life, and taking in plenty of calcium is important. But having enough calcium in one’s diet is a very different thing from too much calcium in the urine.

There are numerous rare metabolic disorders that can lead to too much calcium, uric acid and oxalate in the urine, but these conditions are not usually the cause of stone formation in Americans. To understand the more likely cause, we need to look at the American diet.

Sodium is the most abundant salt in the blood, as well as the hardest working salt in the human body. The kidney is dedicated to holding on to sodium as a first priority. That means the kidney will try to retrieve sodium before it flows out in the urine. For sodium to be reabsorbed from the urine, however, another positively charged compound has to be traded in its place. Calcium is a happy volunteer. So, remember all those tasty processed foods we eat that are loaded with sodium? That sodium gets swapped and ultimately leads to more calcium in the urine. That’s the first strike.

Americans also eat lots of animal protein, especially since the new protein-heavy diets have become popular, and these foods are loaded with purines, which go on to become uric acid in the urine. Remember that uric acid is a Velcro cowboy hat? In addition, the protein load also stimulates breakdown of bone, leading to — guess what? — even more calcium delivered to the urine, while it reduces urinary citrate (swim cap). Strike two.

Now consider fat in the diet. Dietary calcium usually binds to dietary oxalate in the gut, escorting it down the poop highway and out of the body. However, dietary fat also binds to dietary calcium, permitting more oxalate Velcro cowboy hats to freely sneak across the gut into the blood, eventually ending up in the urine. Strike three.

Additionally, dietary sources of oxalate come from the best things in life, like chocolate, nuts, caffeine, alcohol and spinach. Strikes four through eight. Did I mention simple sugars increase calcium in the urine? Yikes.

Sometimes there is simply an overabundance of these calcium/Velcro-cowboy-hat compounds — the compounds that are no longer dissolved become supersaturated and begin forming crystals. Eventually those crystals can bunch up and, voila, you have a kidney stone.

Next, you find yourself in an ER with your child doubled up in a ball of pain in the middle of a puddle of vomit. Then the doctor looks at a urine sample, which contains blood, and orders an ultrasound or CT scan that reveals the culprit. If the stone or stones are small enough, you are sent home with a strainer and a bottle of narcotics. If they are too big to pass, you get to meet a urologic surgeon to discuss various options of breaking up the rock-pile. Oh, it’s a good time.

So what are we to do to prevent this painful ailment? Big surprise, we need to follow the recommended daily allowance (RDA) for calcium and fiber (they bind oxalate in the gut), and fruits and vegetables (they increase the happy hats — citrate and magnesium — in the urine). We need to avoid simple sugars, and follow the RDA for fats and proteins (to reduce calcium and uric acid in the urine). We need to consume the RDA or less of sodium, and the RDA or more of potassium (reducing calcium bobble heads in the urine, and providing potassium bobble heads in the urine for the Velcro cowboy hats to bind to). Finally, there’s on simple thing you can have your kids do: Drink lots of water. The more dilute their urine, the more the compounds are spread out and less likely to form stones.

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