The Kidney-Blood Pressure Connection

It turns out that high blood pressure damages parts of the body that regulate blood pressure. That can have serious consequences for your kidneys and your risk for cardiovascular disease.

As was explained in a recent eSavvyHealth article; chronic kidney disease is known to increase risk for heart attack and stroke, nerve damage, and high blood pressure (needhere). And high blood pressure in turn increases risk of damage to the ¹ here). And high blood pressure in turn increases risk of damage to the heart, arteries, brain and…kidneys! here). And high blood pressure in turn increases risk of damage to the heart, arteries, brain and…kidneys!

If damage to your kidneys can cause high blood pressure, and high blood pressure can damage your kidneys, that’s a vicious circle that can easily spiral out of control—not just for an individual, but for a population. And there are indications that that’s exactly what’s happening. In the US, for example, the incidence of End Stage Renal Disease has skyrocketed over the last 35 years, from roughly 200 people per million to more than 2,000.

Let’s have a look at how kidneys influence blood pressure, and how blood pressure influences the operation of the kidneys.

We’ll start with a question: “Why might the kidneys ‘want’ to influence your blood pressure?” The answer to that is straightforward: your kidneys need to filter all of the blood in your body, several times a day. And while there are about 6 quarts of blood in your body, your kidneys process about 150 quarts of blood each day, meaning that any given ounce of blood would need to pass through your kidneys around 25 times each day. That makes sense if you think about it—energy production and other metabolic processes that generate waste occur continuously in every one of the 30 trillion or so cells in your body. That’s a LOT of waste.

Follow-up question: “What keeps that blood moving through your kidneys?” That answer is also straightforward: it’s blood pressure. If blood pressure drops, then the flow of blood slows down, and if it slows too much then the amount passing through the kidney’s filtration system can drop to the point that wastes accumulate. That can’t be allowed to happen, so the kidneys have the ability to detect blood pressure and increase it when needed. This is done in two primary ways²:

Your kidneys can adjust the salt content of your blood so that your body retains water that would otherwise by expelled, effectively increasing the amount of blood in your system, and
Your kidneys can release a hormone called renin, which in turn activates a chain reaction of other hormones that ultimately stimulate a constriction of your blood vessels (vasoconstriction).

If you think of blood pressure in your arteries as being similar to water in a hose, essentially what your kidneys do is exactly what you would do when you need more pressure—increase the volume of water in the hose, and make the water move through a smaller tube (such as a nozzle) so that it has to go faster.

When your kidneys sense that your blood pressure is high enough to filter blood at the necessary rate, they ease up on increasing salt content and stimulating vasoconstriction. This is the kind of dynamic balance that we see in so many body systems—the correct level or amount of something is maintained by the increased or decreased action of some kind of forcing mechanism.

What’s critical to understand about this is that the mechanism in the kidneys that senses and regulates blood pressure is located in the tiny filters called nephrons that do the kidney’s work³. There are about a million nephrons per kidney, which is enough to do the job even if you lose half of them. As we have just learned, nephrons need a certain level of blood pressure to work properly, but there’s a limit—blood pressure that is too high can damage them.

It is not known exactly what it is in nephrons that is damaged by high blood pressure, but it is known that the effect includes damage to the mechanisms that sense and/or help regulate blood pressure. High blood pressure damages parts of the body that regulate blood pressure. And so the nephrons begin their journey around that vicious circle.

If that’s the problem, what’s the solution? Currently it lies mainly in the use of drugs to control blood pressure. Those drugs are undoubtedly saving and prolonging lives, but like all drugs they have side effects. There is an alternative, though, an approach which depends on asking the old philosophical question: “What came first, the chicken or the egg?”

In the case of kidneys and blood pressure the question becomes “Which happens first, damage to the nephrons or high blood pressure?” Just like the chicken and the egg, the answer isn’t obvious, but one thing IS clear—if you want to avoid the vicious circle, you’ll need to keep your nephrons healthy so they can effectively manage blood pressure. Of course, that means attending to proper nutrition, physical activity, and sleep, but there’s also a line of reasoning that indicates one very specific action you can take:

Chronic kidney disease and high blood pressure have not always been the epidemic that they are now. Which prompts another question: “What has changed over the past several decades that could damage nephrons for an entire population?”

Here’s a clue: chronic kidney disease is a classic symptom of another widespread disease, diabetes, which is essentially the body’s inability to keep blood sugar levels from getting dangerously high. High blood sugar levels can damage blood vessels, including the dense network of tiny blood vessels that are connected to nephrons⁴.

But it’s not just the very high blood sugar levels associated with diabetes that can damage nephrons—according to relatively recent research⁵, even slightly elevated blood sugar levels increase the risk of such damage.

These are indications of a connection between elevated blood sugar, kidney disease, and high blood pressure; there is not yet scientific proof. But if you needed just one more little push to decide to severely limit your intake of added sucrose and high fructose corn syrup in your foods, this just might be the one that takes you over the edge.

It may very well be that the most important filter related to your kidney’s health is the one you employ when you’re deciding what to put into, and leave out of, your grocery cart.

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