Microvascular health is just what it sounds like: the health of your tiniest blood vessels. These are the capillaries, of course, and eventually all the arteries branch down to them.

Capillaries are hardly larger than the various red and white blood cells and biochemicals flowing through them, but they are very numerous. Most of your 50 trillion cells must reside close to a capillary to get their necessary nourishment. Unravel the capillaries and lay them end-to-end, and they go twice around the earth. That’s quite a lot of capillary.

Capillaries clog easily. This does not carry the life-threatening specter of a major clogged heart artery (heart attack) or brain artery (stroke), and indeed, if a few capillaries clog, usually no big deal. But what if a lot of them clog in a specific region? That would cause that region to start to die. Where would this be likely to occur? Generally the extremities: the toes, the fingers, the eyes, the brain, and the kidneys. In the worst cases, this means amputations, blindness, loss of cerebral function, and so on. Not a pleasant picture.

Even though microvascular health issues may lack the drama of heart attacks or strokes, they are perhaps just as important, and unsurprisingly, they respond to the same lifestyle modifications as the big arteries: Anaerobic exercise will significantly improve microvascular function.

Measuring Microvascular Health

We would like to measure this. Autopsies are so uncomfortable we need a less invasive way to assess this feature of our health. Microvascular health would not show up on a scan, but there is an interesting blood number we can use: creatinine. Creatinine is naturally produced bodily junk and one of the kidney’s tasks is to get rid of it. Now the kidneys are very complicated, but one major part is an elaborate strainer, constructed by a huge network of tiny blood vessels. This is a handy microvascular proving ground. If the tiny blood vessels are clear, the kidneys will work well, and creatinine will be removed. If the microvascular health of the kidneys is poor, creatinine levels will rise.

Now the microvascular health of the kidneys is going to be pretty much like the microvascular health everywhere else. So this one measurement is going to give us the big picture—microvascularly speaking. A creatinine level at or above about 1.2 mg/dl is bad. This indicates serious microvascular disease. Often the lab reports will indicate a normal range of 0.7 to 1.2. Ignore that. Anything over 1.0 is a red flag. However, high creatinine levels are reversible. With appropriate exercise, the level can be moved from the danger zone, 1.2, to a very healthy level, 0.9 or even lower. Creatinine should be measured frequently. We recommend quarterly.

Other Kidney Functions

The kidneys also have several hormonal functions. They additionally regulate several key circulating electrolyte levels. Kidney function is very key to overall good health.

How Kidneys Work

Kidneys clean the blood, and in many ways, take up where the liver left off. Items in the blood that the liver has marked for destruction, along with other waste, will be diverted into the urine by the kidneys.

The kidneys are usually billed as a filter, but what they are required to do is a tall order for any sort of filter we are familiar with. First the problem: There is a variety of waste products circulating in the blood. Some of it is known, such as urea coming from the liver, and some is unknown, such as snipped up pieces of a failed bacterial invasion. The size of the trash varies from quite small molecules to fairly large stuff, though most of it is smaller than the circulating red and white blood cells.

So how to go about this? Something like a coffee filter isn’t going to work at all. First, it only lets small stuff through, and second, it clogs up and has to be replaced.

Body cells have a way of expressing what they want from the blood stream. A cell that wants some circulating sugar will actually stick a gadget through its cell wall, called a transporter, which will grab circulating sugar molecules in the blood and pull them into the cell.

With the kidneys, we sort of turn this upside down. The kidneys want to grab what we don’t want, and therein lies a problem. We don’t know what a lot of this stuff is, so the cell transporter solution won’t work: it won’t know what to look for.

How the Kidneys Identify the Circulating Junk

We know they do it, but the solution is so clever, it would take an Einstein to come up with it. Or someone with a very cluttered desk. Did you ever have such a mess on your desk that you didn’t know where to start, so your shoved it all into a grand heap, dumped it into the trash, and then picked through it to recover the things you actually wanted to keep? This is how the kidneys work.

Step one: the kidneys squeeze a lot of the blood fluid (plasma) out of the capillaries, and into the urine. Think of squeezing a sponge. Only the red and white cells and some plasma would be left in the blood. Now obviously there has to be a step two, or we would be running to the bathroom every 90 seconds and would rapidly dehydrate. We shouldn’t even call the squeezed stuff urine, because it’s not going to be the real thing until after step two. So then: “pre-urine.”

Step two: After step one has squeezed some of the blood into the pre-urine, a downstream process recaptures everything that should be retained. Here the kidney is picking through the trash to recover the stuff it wants. This would include most of the water, various electrolytes like calcium, sodium and potassium, and small molecules like amino acids, glucose, etc., and anything else of use. In fact, the recapture is picky. If the blood already has enough salt, the kidneys will just let it go. Hundreds of things are recaptured, at little or no energy cost, and regulated to ideal levels. Anything not taken back goes on to the bladder. Whatever we might notice about urine—color, amount, etc.,—directly reflects what the kidneys decided not to keep in step two.So here the body has killed two birds with one stone. It’s gotten rid of the waste and performed a regulation operation at the same time. Life always finds and refines a way.

Take care of your kidneys by taking care of your microvascular health with proper diet and proper exercise, especially exercise that significantly varies your heart rate.