High blood sugar, also called hyperglycemia, can cause a wide range of side effects. In the short term, you may feel thirsty, need to urinate often, have blurred vision, or feel tired. Over months and years, consistently high blood sugar can damage your nerves, kidneys, eyes, heart, and blood vessels. These long-term complications are serious and often permanent.
What Are The Side Effects Of High Blood Sugar?
The side effects of high blood sugar fall into two main categories: short-term symptoms and long-term complications. Short-term symptoms usually appear when blood sugar rises above 180 mg/dL after a meal or stays high for hours. Long-term complications develop after years of poorly controlled diabetes or prediabetes.
Short-term side effects include increased thirst and urination, dry mouth, blurred vision, fatigue, headache, and unintentional weight loss. In people with type 1 diabetes, very high blood sugar can lead to a dangerous condition called diabetic ketoacidosis (DKA).
Long-term complications affect nearly every organ system. They include nerve damage (neuropathy), kidney disease (nephropathy), eye damage (retinopathy), heart disease, stroke, and poor circulation that can lead to foot ulcers and amputations. These complications are the leading causes of disability and early death in people with diabetes.
What Happens in the Body When Blood Sugar Is High?
When blood sugar is high, your kidneys work to excrete excess glucose through urine. This pulls water with it, causing dehydration and frequent urination. High glucose also damages the lining of blood vessels and triggers inflammation. Over time, sugar molecules attach to proteins and fats in your body, forming harmful compounds called advanced glycation end products (AGEs). AGEs stiffen blood vessels, damage tissues, and speed up aging of organs.
High blood sugar also increases oxidative stress — an imbalance between harmful free radicals and the body’s antioxidant defenses. This process contributes to cell damage throughout your body.
How Does High Blood Sugar Affect the Heart and Blood Vessels?
High blood sugar damages the inner lining of arteries, making them stiff and narrow. This increases your risk of atherosclerosis — the buildup of fatty plaques. Atherosclerosis can lead to coronary artery disease, heart attack, and stroke.
People with diabetes are two to four times more likely to die from heart disease than those without diabetes. High blood sugar also damages small blood vessels, which can reduce blood flow to the legs and feet, causing pain during walking (claudication) and increasing the risk of infections and amputations.
Controlling blood sugar, blood pressure, and cholesterol helps reduce these risks, but some damage can be permanent.
How Does High Blood Sugar Damage the Kidneys?
The kidneys filter waste from your blood. High blood sugar forces the kidneys to filter more blood than normal. Over time, this extra work damages the tiny blood vessels inside the kidneys (glomeruli). Damaged glomeruli leak protein into the urine — an early sign of diabetic kidney disease.
If blood sugar stays high for years, kidney function declines. This condition, called diabetic nephropathy, can progress to chronic kidney disease (CKD) and eventually kidney failure requiring dialysis or a transplant. About 1 in 3 adults with diabetes has some level of kidney damage.
Blood pressure control and medications called ACE inhibitors or ARBs can slow the damage, but they cannot reverse it.
How Does High Blood Sugar Affect the Eyes?
High blood sugar damages the small blood vessels in the retina — the light-sensitive tissue at the back of the eye. This is called diabetic retinopathy. Initially, blood vessels may leak fluid or blood, causing swelling (macular edema) and blurred vision.
As the condition worsens, abnormal new blood vessels grow. These are fragile and can bleed into the eye, leading to sudden vision loss. Diabetic retinopathy is the leading cause of blindness in working-age adults in the United States.
Cataracts (clouding of the lens) and glaucoma (damage to the optic nerve) also occur more often and earlier in people with high blood sugar.
Regular eye exams can catch retinopathy early, and laser treatment or injections can prevent vision loss — but only if caught before severe damage.
How Does High Blood Sugar Damage Nerves?
High blood sugar damages both small and large nerve fibers. This condition is called diabetic neuropathy. The most common type is peripheral neuropathy, which affects the feet and hands. Symptoms include numbness, tingling, burning, or sharp pain. Many people lose sensation in their feet, so they don’t feel injuries or infections.
Autonomic neuropathy affects nerves that control the heart, digestion, bladder, and sexual function. Signs include irregular heart rate, slow stomach emptying (gastroparesis), bladder infections, and erectile dysfunction.
Nerve damage is often irreversible. Tight blood sugar control can prevent or delay it, but once symptoms appear, treatment focuses on managing pain and protecting the feet from injury.
Can High Blood Sugar Side Effects Be Prevented or Reversed?
Many side effects of high blood sugar can be prevented or delayed. For people with prediabetes — blood sugar levels between 100 and 125 mg/dL fasting, or HbA1c 5.7% to 6.4% — weight loss and exercise can often return blood sugar to normal. This prevents progression to diabetes and its complications.
For people with type 2 diabetes, substantial weight loss (15% or more of body weight) can lead to remission — meaning blood sugar returns to normal without medication. However, damage that has already occurred, such as advanced retinopathy or kidney disease, is not reversible.
For type 1 diabetes, remission is not possible because the pancreas no longer makes insulin. Strict blood sugar control with insulin therapy is essential to prevent or slow complications.
Managing blood pressure and cholesterol, taking prescribed medications, quitting smoking, and having regular checkups are all proven ways to protect against the side effects of high blood sugar.
Frequently Asked Questions
Can high blood sugar cause dizziness?
Yes. High blood sugar can cause dehydration, which lowers blood pressure and leads to dizziness. Autonomic neuropathy from chronic high blood sugar can also affect blood pressure regulation and cause dizziness upon standing.
What does high blood sugar feel like?
Common feelings include extreme thirst, frequent urination, tiredness, blurry vision, headache, and dry mouth. Some people feel hot or have trouble concentrating. If blood sugar gets very high, nausea and confusion may occur.
Can high blood sugar go away on its own?
Mild high blood sugar may return to normal if your body produces enough insulin. But if high blood sugar is caused by diabetes, it won’t go away without treatment. Untreated high blood sugar continues to climb and can become dangerous.
What is the fastest way to lower high blood sugar?
For type 1 diabetes, taking a correction dose of rapid-acting insulin lowers blood sugar fastest. For type 2 diabetes, taking prescribed medication and drinking water can help. Exercise also lowers blood sugar, but only if it is not too high — above 240 mg/dL, exercise can actually raise blood sugar further. Always follow your doctor’s plan.
