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High School Chemistry and Kidney Disease (Part 1)

Published: June 17, 2010

The good people at the American Urological Association offered primary care docs a half-day course on updates last Saturday.

At the conference, they reviewed prostate disease, bladder issues, erectile dysfunction and renal stone disease. The lecturers on renal stones offered some of the most eyebrow raising data – at least to this correspondents set of eyebrows. Having suffered through this MOST uncomfortable condition more than once (and when it comes to discomfort we are talking about something that women who have had babies say can be is AS BAD) I was curious about what the data was on prevention.

Almost all renal stones have calcium in them. With this in mind, one piece of advice long served up by doctors has been to cut down on calcium intake. Stone formation depends upon precipitating out these tiny bits of rock from the urine – much like those chemistry experiments when two ions decide they like each other more than they like hanging out in a liquid and would start lining the bottom of your test tube. Though I have endured these painful little rocks I was never sure that simply lowering calcium was the key action needed. It turns out my doubts are now experimentally verified.

Two large studies by Curhan and colleagues show that people with higher calcium intake had LOWER risks of stones. Now, it turns out that about 70% of stones are of calcium oxalate. Oxalate comes in our diets through nuts, spinach, beets, chocolate and tofu. Furthermore, it turns out that the whole precipitation thing, a la high school chem lab, is a good thing, as long as it is occurring in our guts and not our kidneys. Add MORE calcium and you create some calcium oxalate mineral in the intestine, from which it may easily exit the body. In the absence of this calcium, the oxalate can be absorbed into the bloodstream, where it will travel to your kidneys. After your kidneys filter the oxalate, you might see those tiny rocks form where you did not want them – inside the urinary tract.

So as far as prevention is concerned, forget low calcium diets. Additional studies show that lowering sodium, and reducing protein intake can help prevent renal stones, and staying hydrated enough to keep your urine output to about 2 liters (or quarts) a day will keep things flushed well. What I liked best from this lecture was what you can add to you diet that should help. That, however, will have to wait until part 2 of this review.