The Salt of the Earth
According to a news post on our group’s web site, the Centers for Disease Control and Prevention (CDC) are declaring that we Americans are ingesting too much salt. I can’t imagine that this comes as any surprise whatsoever to anybody who has eaten at a fast food restaurant in the last 20 or 30 years.
The subject of salt got me thinking. Several years ago, back in the days when I owned a car that required monthly maintenance by a tow truck and local repair shop, I had a mechanic attempt to explain to me what sort of gunk had built up in some compartment of my engine. He knew I was a doctor, so he tried to bring his explanation down to my level. “It’s just like how salt builds up in your veins and causes a heart attack.” I politely nodded, knowing that any attempt on my part to counter his well-meant allusion would only result in more cash out of my pocket for the plumbing job he had in mind.
As most of you know, salt doesn’t clog your veins. First off, the veins of the body tend not to be the problem. It’s the arteries of the body that bring oxygen and nutrients to muscles and organs. If you clot off an artery to the brain you get a stroke; a blockage in artery to the heart muscle will lead to a heart attack. The venous system brings blood back to the heart and lungs and a blockage in this system causes a whole world of different problems.
Secondly, salt doesn’t build up anywhere in your body. The real plotline to a heart attack goes something like this. Each of us is born with pristine, clean arteries feeding valuable oxygen to each of our cells. By the time we’ve eaten our way through our thousandth greasy burger we have managed to inject enough cholesterol into the thin membrane of cells that line the inside of each artery that blood flow starts to get restricted. This is compounded by other risk factors well known but mainly ignored by the majority of us (smoking, high blood pressure, diabetes, bad luck). One day, for reasons that are not entirely clear, the few cells that cover our cholesterol stash decide they’ve had enough and split apart. At that point it’s like tossing a match into a fireworks factory—when blood comes into direct contact with cholesterol the blood immediate clots and all flow stops. Any cells downstream are starved of oxygen and die away in a matter of minutes to hours.
So the real issue isn’t salt but rather cholesterol. Salt gets rounded up in the heart attack scenario like a usual suspect because it has other bad effects on the heart. Salt causes two major problems with the cardiovascular system.
The first is a simple volume issue. Most of you already have some inkling that more salt equals more fluid. If you haven’t already figured this out just go out to your nearest Mexican restaurant for a plate of cheesy nachos and a couple of margaritas and see how hard it is to get your wedding ring off the next morning. Salt leads to water retention in your body but doesn’t help the extra water stay in your blood stream. Much of the water leaks out of your capillaries into the surrounding tissue, causing swelling in your ankles, fingers, and any other place you might consider unattractive in a bathing suit. This is nothing more than a minor nuisance problem for most of you, but if you’re unlucky enough to have a weak heart the fluid also builds up in the lungs and causes a suffocating shortness of breath that we call congestive heart failure.
The second problem affects only some of us. A subset of the population has something called salt-sensitive hypertension. This means that someone’s blood pressure rises in proportion to the amount of salt in the diet. This characteristic is more common in African-Americans—in those without this genetic predisposition salt doesn’t seem to have any effect on blood pressure. And while salt doesn’t lead to heart attacks, high blood pressure can.
So, in the end, while the effect of salt may be misunderstood, the CDC wants to make it clear that we’re clearly getting too much of it (especially those of us who have a weak heart, high blood pressure, or a strong desire to look good at the beach). Their recommendation is to simply cut back—advice you don’t need to take with a grain of salt.