It’s normal for your blood sugar to rise after you eat. But if you have large blood sugar spikes regularly, it increases your risk of developing a range of diseases, including heart disease.
In this article, we ask how a deliciously sweet, essential molecule can damage your heart.
What is blood sugar?
After eating, your body breaks down carbohydrates into simple sugar molecules: glucose.
Glucose is then shipped through the walls of your gut and into your blood. From there, it’s free to roam around your body in your blood vessels.
Some glucose will get absorbed by muscles and other cells that need it for energy. The rest is stored in cells in liver, muscle, or fat cells.
Every cell in your body needs glucose to work. And to reach those energy-hungry cells, it has to travel through the blood.
However, if levels are high for too long, or if too much reaches the bloodstream at the same time, it can cause problems.
Blood sugar control
Because glucose is both dangerous and necessary, our bodies are well prepared to handle it.
When blood sugar levels rise, your pancreas releases insulin. This hormone helps glucose move from the blood into cells, ensuring that blood sugar levels don’t get too high (hyperglycemia).
However, because cells need glucose to function, the body needs to make sure there is enough glucose in the blood. If it dips too low — hypoglycemia — that can also be dangerous.
Your body needs to keep a tight rein on glucose. If the balance tips in either direction, it can be bad news.
Scientists have now established that a poor blood sugar response is a strong indicator of heart disease risk. But why?
Although researchers are still teasing out the details, animal research and studies in people with diabetes have uncovered some potential mechanisms.
Below, we’ll outline some of the possible ways that blood sugar might damage heart health over time.
To get to the bottom of it, we’ll have to dive into a bit of physiology and chemistry. Hold tight.
Dilate and constrict
The inside lining of your blood vessels is called the vascular endothelium. This single-cell barrier between the blood and the rest of your body plays a number of important roles.
For instance, this layer helps control what compounds move from the blood into the body, such as hormones. It also helps regulate the immune system.
Importantly, endothelial cells control vasoconstriction and vasodilation — how relaxed or constricted the blood vessels are.
In this way, they control how much blood reaches any given part of the body — if the blood vessels constrict, less blood gets through and vice versa.
During exercise, for instance, endothelial cells help the blood vessels in muscles to expand (dilate), which moves more blood, oxygen, and glucose toward the muscles.
Some people develop fatty “plaques” on their blood vessel walls.
This plaque buildup is called atherosclerosis, and it narrows blood vessels, preventing blood from flowing freely around the body. Eventually, atherosclerosis can result in serious health conditions, including heart disease and stroke.
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Back to glucose
OK, so where are we going with this? Well, high blood sugar can interfere with the endothelium’s ability to dilate blood vessels — at least in studies involving people with diabetes and in animal models.
In this way, exaggerated blood sugar responses over the years may increase the risk of plaque formation and, consequently, the risk of heart disease.
There is also evidence that once plaques start forming, glucose spikes play a part in firming them up — which is a bad thing. The process, which is called glycation, happens when sugars stick to proteins.
Over time, glycation produces advanced glycation endproducts (AGE). AGE are associated with diabetes, aging, and blood vessel dysfunction. They most often occur during times of inflammation and oxidative stress — more on both of those later.
Right, that’s the first portion of physiology out of the way. Next, get ready for the chemistry.
How does blood sugar impact vasodilation?
So, blood sugar spikes are linked to heart disease, and it seems that plaques might play a part. But how might glucose be interfering with the endothelial cells?
Here, we meet reactive oxygen species (ROS). These are reactive chemicals formed from oxygen. As our cells make energy, they naturally create ROS, and they’re not all bad.
ROS are important for the day-to-day running of our cells. However, as with many things in life, too much of a good thing can soon turn into a bad thing. So, your cells keep them finely balanced by producing antioxidants to counteract them.
If ROS get out of hand, they cause “oxidative stress,” which damages cells.
Now, back to the main story: Glucose spikes cause an increase in ROS. The increase in ROS leads to oxidative stress, which then impacts the endothelial cells. This increases the risk that plaques will develop, and more plaque means a higher risk of heart disease.
Inflammation, as always
Inflammation is the body’s response to injury or infection. It is a healthy, life-saving reaction.
As with many things in the body, such as glucose and ROS, it needs to be kept under control — too much inflammation over long periods damages the body.
Inflammation underpins many chronic diseases, including type 2 diabetes, some cancers, and heart disease.
In fact, it would be tough to think of a disease where inflammation doesn’t play at least some part.
Glucose spikes also cause inflammation. In a small study, scientists artificially increased blood glucose levels in healthy participants. When they analyzed their blood, they found increased levels of compounds associated with inflammation.
The scientists also found that when they raised participants’ glucose levels and injected an antioxidant at the same time, markers of inflammation were reduced. In other words, ROS may be helping to drive this inflammation, too.
Spikes in blood sugar increase ROS production, which interferes with blood vessel control and increases inflammation. Taken together, over time, this increases the risk of atherosclerosis and, therefore, heart disease.
It's worth repeating: After eating, it's normal for your blood glucose levels to rise and then fall again in the hours afterward.
But when your blood sugar is consistently too high, it can put you at a higher risk of conditions like heart disease and type 2 diabetes in the long term.
Understanding how your body responds to food can help you manage these peaks and reduce your risk.
When you join ZOE, we assess your blood sugar responses to food. We also investigate how your blood fat levels respond and analyze your gut bacteria.
From this information, we can provide personalized nutrition advice to help you minimize blood sugar spikes and move toward your long-term health goals.
For advice on controlling your blood glucose spikes, listen to a recent ZOE Science & Nutrition podcast episode called "How to control blood sugar spikes."
In it, Jessie Inchauspé, a biochemist and blood glucose expert, outlines some simple but effective ways to reduce your blood sugar spikes.
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