Why does blood sugar matter
so much for health?

6 min read

"Blood sugar" is a number you see at your health checkup. For many people, it's a number that means little more than "as long as I don't have diabetes, I'm fine."

But look into blood sugar, and you find that this number is connected to far more of the body than you'd imagine.

The eyes. The kidneys. The nerves. The heart. The brain. And the blood vessels linking them all.

Blood sugar is one of the key indicators of how your body handles energy, and what kind of environment it keeps your blood vessels in.

What is blood sugar, anyway?

Most of the carbohydrates in rice, bread, noodles, fruit and so on are digested into glucose. Glucose enters the blood and is carried around the body. The concentration of glucose in the blood is your "blood sugar."

Glucose itself isn't the bad guy. It's an essential source of energy for staying alive.

The problem is when it stays higher than necessary for a long time.

The key is the blood vessels

Why does blood sugar have anything to do with your eyes, kidneys, nerves, even your heart? One answer is blood vessels.

Blood vessels run throughout the body. Not just to big organs like the heart and brain, but extremely fine vessels in the eyes, the kidneys, and around the nerves. They're like a logistics network delivering oxygen and nutrients.

Chronic high blood sugar is known to damage these vessels and nerves.

Blood sugar → vessels and nerves → the whole body

The small vessels are especially vulnerable

The classic complications of diabetes are retinopathy, nephropathy, and neuropathy.

They look like separate diseases, but the retina and the kidneys are packed with microvessels. Neuropathy, too, involves several factors: not only metabolic problems in the nerves themselves, but damage to the small vessels that feed them.

What changes when blood sugar improves?

In UKPDS 35, which followed people with type 2 diabetes, each 1-point lower updated mean HbA1c was associated with about a 21% lower risk of any diabetes-related endpoint, about 37% lower risk of microvascular complications, and about 14% lower risk of heart attack.

And in the DCCT, in type 1 diabetes, the intensive therapy group had about 76% less onset of retinopathy than the conventional therapy group, about 39% less microalbuminuria, and about 60% less clinical neuropathy.

Both studies were in people with diabetes. You can't apply the same numbers directly to healthy people. Still, they're important data showing how strongly long-term blood sugar is tied to the health of vessels and organs.

It's a continuum, even before a diagnosis

Blood sugar changes continuously from normal to diabetes. Diagnostic criteria draw a line on that continuum for medical decisions.

The DECODE study showed that the 2-hour value of a 75 g oral glucose tolerance test (OGTT) carries prognostic information beyond fasting blood sugar.

That doesn't mean "a slight rise in blood sugar is dangerous." What matters isn't fearing each small fluctuation, but looking at whether your body is handling blood sugar properly over the long term.

Reading your checkup numbers: HbA1c

Blood sugar fluctuates with food, exercise, sleep, stress and more. That's why HbA1c is used. It reflects blood sugar over several months, weighted toward the past one to two months, rather than your last meal.

These aren't for self-diagnosis from a single measurement. Doctors judge by combining test results, symptoms and more.

The goal isn't "never let blood sugar rise"

Blood sugar rising after a meal isn't abnormal in itself. You eat, blood sugar rises, insulin is released, muscles and other tissues take up glucose, and it comes back into the proper range.

What matters is keeping a body that can handle the rise properly.

Muscle is a huge consumer of glucose

Muscle is also a tissue that uses a lot of glucose. Walking, squatting, cycling: when you move your muscles, glucose is used as energy, and regular exercise also improves insulin sensitivity.

The small act of walking 10 minutes after meals

In a randomized crossover trial in adults with type 2 diabetes, walking for 10 minutes after each of breakfast, lunch and dinner was more effective at curbing post-meal blood sugar than walking 30 minutes at once in a day.

A small trial in healthy young adults also found that walking for 10 minutes right after taking glucose lowered the blood sugar peak.

Not everyone will see the same change. Still, it's interesting that the small act of moving a little after a meal can affect blood sugar.

Blood sugar is a number for your future health

The biggest reason to think about blood sugar isn't to shave a few mg/dL off today's number. It's to look at your body over ten, twenty, thirty years.

That's why it's worth knowing your metabolism before symptoms appear, rather than thinking about it once they do.

Blood sugar isn't everything. But you can't ignore it

Blood sugar isn't the only thing that decides the health of your vessels. Blood pressure, LDL cholesterol, triglycerides, smoking, obesity, lack of exercise, sleep, genes: many factors are involved.

Still, blood sugar matters because it's a number that sits where food, exercise, muscle, insulin, blood vessels, and the organs of the whole body meet.

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