back     13th May 2009 Medical Advisory Bulletin      Alphacalcidol

Reducing calcium in the diet of Lowe Syndrome children may not reduce the incidence of Kidney Stones, and may increase the risk.

A reduction of calcium in the diet may paradoxically increase the risk of kidney stones, not decrease and thus is not a good idea. However, calcium should also not be conssumed in excess, especially in between meals, as this can lead to increased absorption in the gut and a higher calcium load to the kidney.

An increased excretion of calcium in the urine is an invariable feature of Lowe syndrome, as also recently documented in our review of our patients (Bockenhauer D, Bokenkamp A, van't Hoff W, Levtchenko E, et al. Renal phenotype in Lowe Syndrome: a selective proximal tubular dysfunction. Clin J Am Soc Nephrol 2008; 3: 1430-1436). The way the kidney handles calcium is, that it iss first filtered in what is called the glomerulus and then needs to be reclaimed (re-absorbed) back into the blood in the renal tubule. The majority of calcium is reclaimed in the part immediately following the glomerulus, which is called the proximal tubule. And this is exactly the part affected in Lowe syndrome. For  this reason, every patient with Lowe syndrome spills extra calcium in the urine. Fortunately, an increased volume of urine is also part of the syndrome, diluting the calcium and thus stones are actually not so common. In our review, 2 of the 16 patients had stones, although about half of all patients had nephrocalcinosis, a deposition of calcium in the kidney.

The key point is, this calcium leak in the kidney is fixed and cannot be improved. I think, the idea of calcium reduction in the diet is, that if less calcium is in the diet, less will come into the blood, less will be filtered by the kidney and less lost. But that is a misunderstanding: calcium is a very important salt in our body and therefore its concentration is tightly regulated by hormones. Therefore, the concentration of calcium in the blood and thus the amount filtered is quite constant. Most of our calcium is stored in our bones. If we reduce the amount of calcium in the diet, so that it doesn't meet our requirements, then hormones will release calcium from the bones to maintain a steady calcium level. This will lead to weakening of our bones . That is one reason, why calcium restriction is not a good idea. The second is, that calcium does not form deposits or stones by itself, but needs partners, such as oxalate, phosphate or carbonate. Only with these partners can it precipitate. Yet this process does not only happen in the kidney, but also in the gut. Therefore, a normal amount of calcium in our diet will precipitate these substances already in the gut and thus prevent absorption of them. Studies in healthy adults have actually shown, that calcium reduction in the diet leads to an increased risk of kidney stones, for exactly this reason.

In summary: reduction of calcium in the diet may paradoxically increase the risk of kidney stones, not decrease and thus is not a good idea. However, calcium should also not be consumed in excess, especially in between meals, as this can lead to increased absorption in the gut and a higher calcium load to the kidney.

Lowe Syndrome Trust Medical Advisory Board