Shahar Madjar, MD

I want to tell you about the relationship between salt consumption, diet and hypertension. But first I wanted to teach you how to fool a baboon into showing you where to find water in the desert.

I learned about the baboon watching the movie Animals are Beautiful People.The movie, a nature documentary by Jamie Uys, came out when I was about 10, and the fact I remember so clearly, decades later, is a testament to its entertaining qualities.

In one of the more memorable scenes, a Bushman is seen wandering in the treacherous Kalahari desert. He is distressed, worried, and, mostly, thirsty. “The baboons always have a secret supply of water,” the narrator says, “and they are not going to tell anyone where it is.” The man makes sure that the baboon is watching him. He creates a deep hole in what seems to be an old tree trunk and drops watermelon seeds into a hollow within it. The baboon, watching from a distance, becomes “incurably inquisitive … and burning with curiosity … he has got to know what’s in there.” The man hides behind a tree and waits for the baboon to make its move. The baboon approaches the tree, reaches into the hollow through the narrow opening, and grasps a fistful of the watermelon seeds, but now, his clenched fist holding the seeds is too large to pass through the hole. The man quickly approaches the baboon, shakes his wrist so it will let go of the seeds and ties him on a leash. The baboon becomes the man’s prisoner.

The Bushman then feeds the monkey salt. Because salt is scarce in that part of the world, the baboon devours the salt. The next morning, the prisoner becomes a mighty thirsty baboon. The Bushman sets the baboon free and follows him. They both run fast along the hot, arid land, and into the secret cave where plentiful, fresh water is found.

The same principle–a linkage between salt consumption and thirst–is applied at your local bar. You get free salted peanuts. Your body tells you that you are thirsty. You buy more beer.

I was reminded of the thirsty baboon story just recently, when I read in the New England Journal of Medicine, about the connections between salt, thirst, and blood pressure. Here are the highlights:

Our table salt is a compound made of sodium and chloride (NaCl). Despite significant variations in salt and water consumption, our body maintains a very steady level of sodium. Every deviation from this steady level of sodium would result in a physiological disaster, even death. To keep this steady state–a constant level of sodium–our kidneys adjust the amount of sodium they excrete (Medical term for expel, or eliminate) to the consumption of salt.

Here is a simplified explanation to what is happening in our body after we consume salt: Almost immediately after consumption of salt, our body absorbs it through the intestine, and the level of sodium in our blood increases. In an attempt to reach a new balance, water from our cells move into our blood. The volume of our blood increases. Pressure sensors within the walls of our blood vessels and in our kidneys quickly sense the expansion in the volume of fluid within our vessels. The cells within these pressure sensors release hormones that send a message to the kidneys. The massage reads: balance the level of sodium immediately! In response, the kidneys excrete more sodium into the urine. And equilibrium is restored.

Higher salt intake–in baboons, bar patrons, practically every animal–stimulates the sensation of thirst, increases fluid consumption, and eventually results in increased urinary volume.

Even in people with normal kidneys there is a delay between the consumption of salt and the response of the kidneys. But in patients with chronic kidney disease, and altered kidney function, the time needed in order to reach a steady state after excessive consumption of salt is longer. Until the state of equilibrium is restored, the increased blood volume exerts more force against the walls of blood vessels leading to high blood pressure, or hypertension.

Can a diet help? In my next article, I will tell you about the DASH diet (Dietary Approaches to Stop Hypertension). Is it effective in the treatment, or the prevention, of hypertension? Does it lead to weight loss? Can it prevent heart disease, stroke, even death? I will tell you more in my next article.

Editor’s note: Dr. Shahar Madjar is a urologist at Aspirus and the author of “Is Life Too Long? Essays about Life, Death and Other Trivial Matters.” Contact him at smadjar@yahoo.com.