The Body Does Not Hold an Exact Number

"The numbers keep going up and down — is that all right?"

People who bring their test results in ask this often. Before I answer, I tell them how the body regulates in the first place.

The body cannot hold an exact number

It is easy to think the body works to keep blood sugar or blood pressure at a set figure. But tens of trillions of cells are each in different circumstances, and no regulation can hold all of them to one value.

So what the body does is different. It decides which way to go, and how fast to go there. It regulates by direction and speed rather than by an exact number.

Keeping the inside steady is called homeostasis. The word is easily read as holding a value exactly in place, but that is not how it works. It is closer to finding stability through change.

The body has a device that reads speed

This is not a figure of speech. Such a device exists.

Look at how the pancreas releases insulin: it reads not only how high the blood sugar is but how fast it is rising. In human islets, the amount of the first insulin release varied with the slope at which glucose rose. Reaching the same figure slowly or steeply changes how much comes out.

Blood pressure is the same. There is a device in the vessels of the neck that measures pressure, and it responds not only to the average pressure but to the rate at which pressure changes.

In two places — blood sugar and blood pressure — separate devices that read "not the value but the rate of change" have been confirmed. It means the body treats speed as something that matters.

So a fast rise brings a large fall

Regulating by direction and speed makes it hard to stop exactly. Usually it goes a little too far.

When blood sugar rises steeply the body answers steeply. Then it can end up lower than where it started. In a study of adolescents given a high-glycaemic-index meal, insulin rose, blood sugar then fell below its starting point, and adrenaline rose — all observed within the one study.

What follows matters. To bring the lowered sugar back, the body sends signals that raise it. Adrenaline goes first, and when it drags on, cortisol backs it up.

The signal goes out, the effect stays

This is the part I watch.

Adrenaline is gone from the blood within minutes. Yet after that signal has gone, the liver keeps putting out glucose and the muscle keeps taking in less of it. In fact the liver's output peaks at around thirty minutes and is back to baseline by three hours — and blood sugar still does not come down. The side that uses glucose is being held back.

One more thing overlaps here. Adrenaline does not rise alone; cortisol rises with it. Cortisol lays the ground for adrenaline to have its effect, and slows the dispersal of adrenaline around the tissue. One hormone making another hormone's work possible is called a permissive effect.

The difference shows plainly in blood sugar. Given to people one at a time, the hormones that raise blood sugar lift it a little and stop. Given together, blood sugar rose more than three times the sum of each — even as insulin rose sharply.

The signal is off but the result is still there. What pushes it up and what holds it up are not the same. So once raised, blood sugar does not come down easily, and one wide swing tends to be followed by another.

Held high too long, the receiving places thin out

In people where this swinging repeats over a long time, insulin resistance and impaired glucose tolerance are seen alongside it. Which comes first has not been settled.

One piece is clear, though. When insulin stays high for a long time, the places that receive it grow fewer. This has been confirmed in human muscle.

Short of it, the body adds receiving places; awash in it, the body takes them away. The body is always changing its own sensitivity to suit the circumstances. The same thing on the nerve side I have written down in Tired and Yet So Easily Upset.

Blood pressure has the same shape

It is easy to put rising blood pressure down to stiffened vessels alone. But there is another side.

When less blood reaches the kidney, the body raises the pressure to make up for it. This has been established for a long time. Whether something similar happens for the brain is being studied lately, though that side is not settled.

It is a view that makes blood pressure look less like a raised number and more like an adjustment made to protect something.

In the consulting room I look at the range

I look less at a single figure than at the width and the speed of the swing. I ask when they eat and when they get worse, and which part of the day differs.

Two bodies with the same average are in different states if one moves gently and the other swings steeply. What I want to work on is not the value but that width.

When to see a doctor first

If cold sweats, trembling hands and a fading feeling keep returning, if weight drops without reason, or if you have started drinking unusually large amounts of water — before a story like this, examination and testing come first. If you are on medication, do not adjust it yourself; speak with whoever prescribed it.

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Sources

• Hypoglycaemia — symptoms and what to do — Asan Medical Center
• A study measuring that in human islets the first insulin release varies with the speed at which glucose rises — American Journal of Physiology – Endocrinology and Metabolism, 2025
• A piece setting out the view that when an organ receives too little blood the body raises pressure to make up for it — Future Cardiology, 2016

Written by Dr. Heo Ji-young (Ph.D. in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)