On Kidney Stones: Math Professor Fails to Pass Calculus


By Stan Wagon

What a great headline! Unfortunately for me (the math professor) the “calculus” here refers to a kidney stone, not a study of speed and acceleration. Many runners have suffered from kidney stones. In 1980 and 1983 I had my first stones (I was road racing in the hot Massachusetts summer) and I had a couple more between 2000 and 2003. I tried to stay hydrated but what with long backpack trips in the deserts of Utah or the snows of British Columbia, it was not always easy. All of these passed on their own and, while painful, their passage is not a big problem as the stones were not very large (about 2 mm).

I was clean from 2003 until 2015, but then I had one in June 2015 (it passed) and one in December 2016. This last one did not pass and required intervention to remove it (you don’t want to know the details; suffice it to say that the procedure was not pleasant).

There are some conditions that cause stones to form from other minerals, but the most common type for runners, or the general public, is one made of calcium oxalate. While causes can vary depending on an individual’s metabolism and diet, for most runners the precipitating factor will be dehydration; so the obvious way to minimize this sort of calculus is to stay well hydrated.

There has been occasional mention of certain foods as being good (or bad) for the kidneys. Calcium is an interesting case. After my first stone I was told to cut back on milk products. But a few years later it was realized that calcium actually hinders the formation of stones since it binds some oxalate in the stomach, stopping it from entering the bloodstream and reaching the kidneys. Going on a low-oxalate diet is not recommended, since so many good and healthy foods, from strawberries to almonds to sesame seeds to spinach, are high in oxalate. Spinach is by far the highest, so avoiding that perhaps makes sense.

But there is a new approach that my urologist recommended and it looks very promising. Of course, hydration is still key and we should all watch that, but as a secondary preventive step, taking one or two potassium citrate capsules a day seems like a very good idea. The reason is that oxalate levels in the urine appear, not surprisingly, to be an indicator of the possibility of oxalate stone formation. So reducing oxalate levels in the blood, but without massive dietary changes, seems like a good idea. A citrate supplement, and potassium citrate seems to be the most recommended, accomplishes this. It is available over-the-counter but it would be reasonable to consult a doctor, preferably a urologist, before taking it; such supplements can cause side effects.

In 2003 my urine oxalate level was 90 mg/day (normal is under 45). In January 2016, just after my last stone, it was 70. Then after six months on potassium citrate it was down to 45, and six months later it is at 42. Measurement of the oxalate level requires a 24-hour urine collection. There are other tools to check on stone status, and an X-ray shows there are no stones-in-residence in my kidneys waiting to break off and cause problems. Sometimes ultrasounds are used to detect these, but X-rays work well.

As regards hydration, runners surely know by now that taking in massive amounts of water without electrolytes is a bad idea, and can lead to the serious imbalance known as hyponatremia. At least one ultramarathoner I know of has been hospitalized for this but that was decades ago. The use of electrolyte-enhanced liquids is common today and they help maintain proper electrolyte balance.

Stones are not always small. If they are large they will not pass naturally and surgical or other intervention is needed. So if you have a lot of pain and you suspect a stone you should go to the emergency room within a few hours. Some other important points:

  • Women seem less prone to kidney stones than men.
  • Large stones do occur and can require some sophisticated intervention. Obviously, it is best to avoid them.
  • It is possible, with a glass measuring device, to measure the specific gravity of one’s urine. Color (the paler the better) is a much easier way to evaluate this.
  • Blood in the urine can indicate that a stone has popped off the kidney and is making its way down.
  • The typical time of onset of kidney stone formation (and I can confirm this) is around 5 a.m. after a night’s sleep.

The pain seems to be caused as much by the backup pressure of liquid in the kidney due to the blockage, as opposed to the passage of the stone through the ureter, which connects the kidney to the bladder. Once a stone makes it to the bladder, the final passage to the outside world is easy. One can use a filter to capture it for analysis or to serve as a souvenir to remind one to drink more water.
Stan Wagon is a co-founder of UltraRunning Magazine who remains active with endurance sports – especially on snow in the Colorado Rockies.


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