The “gold standard” in determining how much sodium you eat is how much you excrete. If healthy, the kidney processes many times over the amount of sodium a person ingests but excretes almost exactly the amount taken in. “Everyone” knows that! All medical studies of dietary sodium are concerned about how to measure intake since sodium isn’t something discrete like a banana or apple; it’s consumed in very small amounts in virtually everything. Dietary recall has become a refined art, but most scientists agree that even the best recall techniques pale in accuracy to measuring urinary sodium – the “gold standard.”
In recent years, however, much like other “truths” we’ve “known” about sodium, our knowledge is becoming a bit less ironclad. The May-June issue of Seminars in Dialysis carries an iconoclastic article by German nephrologist Jens Titze, “Water-free sodium accumulation ” questioning the concept that the amount of steady-state sodium in the body is unchanging. Titze suggests that “large amounts of Na+ can be accumulated” which “provides an extrarenal regulatory alternative in the maintenance of body fluid volume and blood pressure control.” Titze’s conclusion:
The physiology and pathophysiology of body Na+ distribution is more complex than believed. Therefore, clinical concepts based on oversimplified two-compartment models of Na+ balance must be experimentally re-evaluated.
Earlier studies of German astronauts and others have suggested much the same. It’s far too early to jettison our reliance on urinary sodium measurement, but it should remind us that science is ever evolving as we push back the shadows of the unknown.
I’m off to China in a few weeks for a worldwide Salt Symposium. In preparation, I’m auditing a course on Chinese history (“From Yao to Mao” --Tang Yao, not Yao Ming!). One of the study segments compares Confucianism with Taosim and the lesson seems apropos. Confucian thought was very orderly and hierarchical; people should conform to the “known.” Tao thought, to the contrary, is more skeptical, questioning whether we really understand the full nature of anything we think we “know.”
Thus, the “gold standard” of urinary sodium and concept of sodium homeostatis are Confucian and Titze and other skeptics have a Taoist strain.
With regard to our current controversy over dietary sodium, the National Heart, Lung and Blood Institute would represent the Confucian approach of bestowed truth while groups like the Cochrane Collaboration and other skeptics about conclusions being drawn from available evidence, embody a Taoist approach.
All of us, whether we readily accept and revere authority or revel in the flaws inherent in our quest for understanding, should use these small events as useful reminders of the larger need to remain humble and teachable in our approach to life.
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