Diabetes is a condition of high blood sugar. Whether someone has Type 1 or Type 2 diabetes, the core problem is the same: glucose builds up in the bloodstream instead of getting into cells where it’s needed for energy. That said, people living with diabetes can also experience dangerously low blood sugar, usually as a side effect of the medications used to treat the condition. Understanding both sides matters.
Why Diabetes Means High Blood Sugar
Your body runs on glucose, a sugar that comes from the food you eat. To get from your bloodstream into your cells, glucose needs insulin, a hormone made by your pancreas. Think of insulin as a key that unlocks cell doors so glucose can enter. Without that key, glucose has nowhere to go and accumulates in your blood.
In Type 1 diabetes, the immune system attacks the insulin-producing cells in the pancreas, destroying the body’s ability to make insulin at all. In Type 2 diabetes, the pancreas still makes insulin, at least initially, but the cells in your muscles, liver, and fat stop responding to it properly. This is called insulin resistance. One useful analogy: it’s like having the right key, but the lock is sticky. Eventually the key stops working altogether. Either way, the result is chronically elevated blood sugar, the medical term for which is hyperglycemia.
The Numbers That Define Diabetes
Normal fasting blood sugar (measured after at least eight hours without eating) is below 100 mg/dL. Prediabetes falls between 100 and 125 mg/dL, and diabetes is diagnosed at 126 mg/dL or higher. Another common test, the A1C, measures your average blood sugar over roughly three months. Normal is below 5.7%, prediabetes is 5.7% to 6.4%, and diabetes is 6.5% or higher.
If you already have diabetes, the typical daily targets are 80 to 130 mg/dL before a meal and less than 180 mg/dL two hours after a meal starts.
What Sustained High Blood Sugar Does to Your Body
When blood sugar stays elevated over months and years, it damages blood vessels and nerves throughout the body. The consequences are widespread. Your eyes can develop problems that eventually lead to vision loss or blindness. Your kidneys can deteriorate to the point of needing dialysis or a transplant. Nerve damage causes pain, burning, tingling, and numbness, particularly in the feet, and can also affect digestion and sexual function in men.
High blood sugar also raises the risk of heart attack and stroke by making blood pressure and cholesterol harder to control. Foot sores and infections can become severe enough to require amputation. The immune system weakens, making common infections more dangerous. Diabetes also increases the risk of dementia and osteoporosis. These complications develop gradually, which is why keeping blood sugar within target ranges matters so much over the long term.
Why Low Blood Sugar Happens Too
Here’s where things get confusing for many people. Diabetes itself is defined by high blood sugar, but the treatments used to bring blood sugar down can sometimes overcorrect, pulling glucose levels too low. This is called hypoglycemia, and it typically happens when someone takes too much insulin or certain other diabetes medications. The medication causes cells to absorb too much glucose from the bloodstream, leaving too little circulating.
Insulin is the most common culprit, but other medication types can also trigger low blood sugar, especially a class called sulfonylureas. Skipping meals, exercising more than usual, or drinking alcohol while on these medications increases the risk.
How High and Low Blood Sugar Feel Different
High blood sugar tends to develop slowly. You might notice increased thirst, frequent urination, blurry vision, and fatigue. Because these symptoms build gradually, some people live with elevated blood sugar for years before realizing something is wrong.
Low blood sugar feels very different and comes on fast. When glucose drops below about 70 mg/dL, your body releases adrenaline as an emergency response. That surge of adrenaline is what causes the classic symptoms: shakiness, sweating, a pounding heart, anxiety, and dizziness. As blood sugar drops further, the brain starts running short on fuel, leading to confusion, slurred speech, blurred vision, coordination problems, and in severe cases, seizures or loss of consciousness. Sudden hunger and irritability are also common early warning signs.
Treating a Low Blood Sugar Episode
Because low blood sugar can become dangerous quickly, people with diabetes who take insulin or certain medications learn to respond using the 15-15 rule. You eat or drink 15 grams of fast-acting carbohydrates (about four glucose tablets, half a cup of juice, or a tablespoon of honey), then wait 15 minutes and recheck your blood sugar. If it’s still below 70 mg/dL, you repeat the process. Once blood sugar is back in the target range, a balanced snack or small meal with protein and carbohydrates helps keep it stable.
High blood sugar, by contrast, is managed over the longer term through medication adjustments, dietary changes, and physical activity rather than a single quick fix.
The Short Version
Diabetes is fundamentally a disease of high blood sugar caused by problems with insulin production or insulin response. Low blood sugar is not the disease itself but a potential side effect of treating it. Both extremes are dangerous, but they feel different, develop on different timescales, and require different responses. If you’re monitoring blood sugar, knowing what both ends of the spectrum look and feel like helps you act quickly when something is off.