Shahar Madjar, MD

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

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

In one of the most memorable scenes, a Bushman is seen wandering the dangerous Kalahari Desert. He is upset, worried and, above all, thirsty. “Baboons always have a secret water supply”, says the narrator, “and they won’t tell anyone where it is.” The man makes sure the baboon is watching him. He creates a deep hole in what appears to be an old tree trunk and drops watermelon seeds into a hollow inside. The baboon, looking from afar, becomes “incurably curious…and burning with curiosity…he must know what’s inside.” The man hides behind a tree and waits for the baboon to move. The baboon approaches the tree, reaches into the hollow through the narrow opening, and grabs a handful of watermelon seeds, but now his clenched fist holding the seeds is too big to fit through the hole. The man quickly approaches the baboon, shakes his wrist to release the seeds, and ties him on a leash. The baboon becomes the prisoner of man.

The Bushman then feeds the monkey salt. Because salt is scarce in this part of the world, the baboon devours the salt. The next morning, the prisoner becomes a thirsty baboon. The Bushman releases the baboon and follows him. They both run quickly along the hot, arid land and into the secret cave where there is plenty of cool water.

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

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

Our table salt is a compound made up of sodium and chloride (NaCl). Despite significant variations in salt and water consumption, our body maintains a very stable sodium level. Any deviation from this constant level of sodium would result in physiological disaster, even death. To maintain this state of balance – a constant level of sodium – our kidneys adjust the amount of sodium they excrete (medical term for expelling or eliminating) to salt intake.

Here is a simplified explanation of what happens in our body after consuming salt: almost immediately after consuming salt, our body absorbs it through the intestine and the level of sodium in our blood increases. In an attempt to achieve a new balance, water from our cells moves into our blood. The volume of our blood increases. Pressure sensors located in the walls of our blood vessels and in our kidneys quickly detect the expansion of fluid volume in our vessels. The cells of these pressure sensors release hormones that send a message to the kidneys. The massage reads: Balance the sodium level immediately! In response, the kidneys excrete more sodium in the urine. And the balance is restored.

Higher salt intake – in baboons, bar patrons, virtually all animals – stimulates feelings of thirst, increases fluid intake, and ultimately results in increased urine volume.

Even in people with normal kidneys, there is a delay between salt intake and kidney response. But in patients with chronic kidney disease and impaired kidney function, the time to reach a steady state after excessive salt intake is longer. Until the state of balance is restored, the increased blood volume exerts more force against the walls of the 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 prevention of hypertension? Does it lead to weight loss? Can it prevent heart disease, strokes, or even death? I will tell you more about it in my next article.

Editor’s note: Dr. Shahar Madjar is a urologist at Aspirus and author of “Is life too long? Essays on life, death and other trivial subjects. Contact him at smadjar@yahoo.com.