Diabetes is actually a condition of high blood sugar, not low. The hallmark of both type 1 and type 2 diabetes is too much glucose building up in the bloodstream because the body either can’t produce insulin or can’t use it effectively. A fasting blood sugar of 126 mg/dL or above is used to diagnose diabetes, well above the normal threshold of 99 mg/dL or below. However, low blood sugar is a common and sometimes dangerous side effect of diabetes treatment, which is where much of the confusion comes from.
Why Diabetes Means High Blood Sugar
In type 1 diabetes, the pancreas can’t produce insulin at all. In type 2 diabetes, the pancreas doesn’t produce enough insulin to keep blood sugar stable. In both cases, glucose accumulates in the bloodstream instead of entering cells where it’s needed for energy. This state of elevated blood sugar is called hyperglycemia, and it’s the defining feature of diabetes.
Left untreated, sustained high blood sugar interferes with protein function, damages blood vessel walls, and suppresses normal immune responses. Over time, this leads to the complications most people associate with diabetes: nerve damage, kidney disease, vision problems, and cardiovascular disease.
How Diabetes Treatment Can Cause Low Blood Sugar
Here’s where things get counterintuitive. While diabetes itself is a high-blood-sugar condition, many of the medications used to treat it can push blood sugar too far in the other direction. Insulin is the most common culprit. When someone takes insulin to lower their blood sugar but eats less than expected, exercises more than usual, or miscalculates a dose, their blood sugar can drop below 70 mg/dL, which is the clinical threshold for low blood sugar (hypoglycemia).
Insulin isn’t the only medication that can trigger a low. Several other drug classes carry this risk, including sulfonylureas and glinides, both of which stimulate the pancreas to release more insulin. People with type 1 diabetes experience low blood sugar more frequently than those with type 2, largely because they depend entirely on injected insulin. But anyone on insulin or certain oral medications can have episodes.
Recognizing Low Blood Sugar
Low blood sugar tends to come on quickly and produces unmistakable physical symptoms. The most common signs include a fast heartbeat, shaking, sweating, sudden hunger, dizziness, and feeling anxious or irritable. These happen because your body is releasing stress hormones to try to push glucose levels back up.
The American Diabetes Association classifies hypoglycemia into three levels:
- Level 1: Blood sugar between 54 and 69 mg/dL. You’ll likely feel symptoms but can treat it yourself.
- Level 2: Blood sugar below 54 mg/dL. At this point, the brain isn’t getting enough fuel, causing confusion, difficulty walking, and blurred vision. This requires immediate action.
- Level 3: A severe event where you need someone else’s help to recover. Seizures and loss of consciousness can occur regardless of the exact number on the meter.
How to Treat a Low
The standard approach is called the Rule of 15: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then check your blood sugar again. If it’s still below 70 mg/dL, repeat the process. Fifteen grams of carbohydrates translates to about four glucose tablets, half a cup of juice, or a tablespoon of honey. Once your blood sugar stabilizes, eating a small snack with protein or fat helps prevent another drop.
Low Blood Sugar Without Diabetes
Low blood sugar can also happen in people who don’t have diabetes, a phenomenon sometimes called reactive hypoglycemia. This typically occurs a few hours after eating and may be tied to what or when someone ate. Other possible causes include alcohol consumption, prior bariatric surgery, inherited metabolic conditions, and, rarely, certain tumors. For most people without diabetes who experience occasional shakiness or lightheadedness after skipping meals, the cause is usually straightforward and resolves with food.
Why Both Extremes Are Harmful
Managing diabetes is essentially a balancing act. Chronically high blood sugar damages blood vessels, nerves, and organs over months and years. Low blood sugar, on the other hand, is an acute emergency that can impair brain function within minutes. Research on surgical patients found that both glucose below 71 mg/dL and glucose above 140 mg/dL independently predicted higher rates of complications, reinforcing that the goal is staying within a middle range rather than simply driving numbers down as low as possible.
Repeated episodes of low blood sugar carry their own long-term risks, including a blunted ability to feel symptoms the next time it happens. This condition, called hypoglycemia unawareness, makes future lows more dangerous because you lose those early warning signs like shakiness and sweating that would normally prompt you to eat something.