Every cell in your body needs energy to function. The main source of energy might come as a surprise: It’s sugar, also known as glucose. Blood sugar is essential to proper brain, heart, and digestive function. It even helps keep your skin and vision healthy.

When your blood sugar levels fall below the normal range, it’s called hypoglycemia. There are many identifiable symptoms of low blood sugar, but the only way to know if you have low blood sugar is by taking a blood glucose test.

Learn more about the symptoms of low blood sugar, as well as the long-term effects on the body.

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The most common reasons for low blood sugar are some medications used to treat diabetes, such as insulin.

In type 1 diabetes, the pancreas can no longer produce insulin. In type 2 diabetes, the pancreas doesn’t make enough insulin, or your body can’t use it properly. Too much insulin or oral diabetic medication can lower the blood sugar level, leading to hypoglycemia.

However, contrary to popular belief, low blood sugar isn’t exclusive to diabetes, though it is rare. It can also happen if your body makes more insulin than it should.

Another possible cause of low blood sugar is drinking too much alcohol, especially over long periods of time. This can interfere with the liver’s ability to create a buildup of glucose and then release it into your bloodstream when you need it.

Other causes include:

When your blood sugar levels are too low, your cells become starved for energy. At first, you might notice minor symptoms, such as hunger and headaches. However, if you don’t get your blood sugar levels up in time, you may be at risk for serious complications.

To keep blood sugar levels from rising too much — called hyperglycemia — you need the right amount of insulin. With insufficient insulin, your blood sugar levels rise. On the other hand, too much insulin may cause your blood sugar to drop quickly.

Read on to learn how low blood sugar affects your body systems.

Digestive, endocrine, and circulatory systems

After you eat, your digestive system breaks down carbohydrates and turns them into glucose. Essentially, glucose is your body’s fuel source.

As your sugar levels rise, your pancreas releases a hormone called insulin, which helps glucose get taken up and used by cells throughout your body. If you have insulin-dependent diabetes, you must take the right about of insulin to get the job done.

Any excess glucose goes to your liver for storage.

When you go a few hours without eating, blood sugar levels go down. If you have a healthy pancreas, it releases a hormone called glucagon to make up for the absence of food. This hormone tells your liver to process the stored sugars and release them into your bloodstream.

If everything works as it should, your blood sugar levels should remain in the normal range until your next meal.

Insufficient blood sugar levels can cause a rapid heartbeat and heart palpitations. However, even if you have diabetes, you may not always have obvious symptoms of low blood sugar. This is a potentially dangerous condition called hypoglycemia unawareness. It happens when you experience low blood sugar so often that it changes your body’s response to it.

Normally, low blood sugar causes your body to release stress hormones, such as epinephrine. Epinephrine is responsible for those early warning signs, like hunger and shakiness.

When low blood sugar happens too frequently, your body may stop releasing stress hormones, called hypoglycemia-associated autonomic failure, or HAAF. That’s why it’s so important to check your blood sugar levels often.

Oftentimes, low blood sugar can signal immense hunger. However, sometimes low blood sugar can make you lose interest in a meal, even if you’re hungry.

Central nervous system

Low blood sugar levels can also cause a variety of problems within your central nervous system. Early symptoms include weakness, lightheadedness, and dizziness. Headaches can occur from a lack of glucose, especially if you have diabetes.

You may also feel signs of stress, such as nervousness, anxiety, and irritability. When blood sugar levels drop during the night, you may have nightmares, cry out during sleep, or other sleep disturbances.

Lack of coordination, chills, clammy skin, and sweating can happen with low blood sugar. Tingling or numbness of the mouth are other effects that may develop. Additionally, you may experience blurred vision, headache, and confusion. Everyday tasks and coordination prove to be difficult too.

Untreated, severe low blood sugar can be very dangerous. It can result in seizures, loss of consciousness, or death.