Diabetes Management

What Level of Blood Sugar is Dangerous?

Diabetes mellitus, more commonly referred to as diabetes, is a disease that is, unfortunately, becoming increasingly well-known.

Diabetes is a disease affecting the pancreas and its ability to produce the hormone insulin. When the insulin-producing cells of the pancreas are destroyed, or when the body doesn’t respond to insulin as well as it should, blood sugar levels rise, and diabetes can develop. 

Insulin helps blood glucose (blood sugar) enter our cells, which is used as fuel to support all of the body’s functions. Without enough insulin, sugar remains in the bloodstream and can become dangerously high. Having high blood sugar over a prolonged period of time is detrimental to health. 

There are two types of diabetes, type 1 and type 2. Type 2 diabetes is the most common and is linked to insulin resistance. It is more likely to be passed along genetically, and can also occur due to lifestyle factors, such as a sedentary lifestyle. 

People can also have a condition called prediabetes, which is when blood sugar levels are slightly elevated, but not enough to be considered diabetes. People with prediabetes are at increased risk of developing type 2 diabetes later on.

Knowing what level of blood sugar is dangerous is important for people with diabetes to stay healthy and prevent complications.

It can also be beneficial for people without a diabetes diagnosis, since knowing what your blood sugar levels are like can lead to earlier intervention for previously undiagnosed blood sugar problems.

What is hyperglycemia?

Hyperglycemia is the term for high blood glucose (sugar) levels. While having sugar in our blood is necessary for survival, having too much blood sugar is unhealthy and can lead to health problems if it remains high over a long period of time.

The definition of high blood sugar depends on what time the blood sugar level is measured, and is measured in milligrams per deciliter, or mg/dL. For people without diabetes, blood sugar levels are considered high when they are greater than 100 mg/dL when fasting (no eating or drinking anything besides water for at least eight hours) or greater than 140 mg/dL within 2 hours of starting a meal. 

When someone has diabetes, blood sugar is considered high if it’s above 130 mg/dL before eating, and above 180 mg/dL 1-2 hours after starting a meal based on the American Diabetes Association guidelines. 

However, the  American Association of Clinical Endocrinologists (AACE) has stricter guidelines for hyperglycemia. AACE considers fasting blood sugar of 110 mg/dL or higher as high as a blood sugar of 140 or higher two hours after a meal.

hemoglobin A1c test measures the average blood sugar over the past 2-3 months in the form of a percentage. An A1c of 5.7%-6.4% is considered borderline high, and an A1c of 6.5% or higher is in the diabetes range. The higher the A1c, the higher the average blood sugar, indicating chronic hyperglycemia.

What causes hyperglycemia?


The most common cause of hyperglycemia is diabetes. Diabetes is classified as type 1 or type 2, with type 2 being the most prevalent type. Type 1 diabetes, also called juvenile-onset diabetes, is often diagnosed before age 18. 

Type 1 diabetes is an autoimmune disorder where the body attacks the cells of the pancreas responsible for producing the hormone insulin. People with type 1 diabetes must inject insulin daily in order to manage their blood sugar levels and stay healthy. The risk factors for type 1 diabetes tend to be more genetic and environmental than lifestyle-related.

Type 2 diabetes is the most common type of diabetes and is, unfortunately, rising in prevalence. According to the Center for Disease Control, 90-95% of people with diabetes in America have type 2.

Type 2 diabetes occurs when the body doesn’t respond to insulin well or doesn’t produce enough insulin. The risk factors for type 2 diabetes are more well-established than those for type 1 and include age, body stature, race, and family history.  

Prediabetes is a condition where blood sugars are considered high, but not high enough to be diagnosed as diabetes. Having prediabetes is a major risk factor for developing type 2 diabetes later on. 

Gestational diabetes (GDM) is diabetes during pregnancy. Many women develop insulin resistance during pregnancy from the massive hormonal changes and receive a diagnosis of GDM without previously having diabetes. Blood sugar levels often return to normal after delivery, but women with GDM are at higher risk of developing type 2 diabetes later in life.

Non-diabetes related

Certain medications can cause short-term hyperglycemia, even in people without diabetes. Steroids are one of the most well-known medications that increase blood sugar. People who take steroids consistently for a long period of time are more likely to experience insulin resistance and blood sugar issues.

Illness and stress can also increase blood sugar in people with and without diabetes. When the body is under stress, certain hormones are released that trigger the body to increase blood sugar. Patients hospitalized or have undergone major surgery can have temporarily increased blood sugar levels until their illness or injury resolves.

What are normal blood sugar levels before and after eating?

For people with and without diabetes, blood sugars should be less than 130 mg/dL before eating to be considered normal. People without diabetes should ideally have blood sugars in the low 100’s or lower before meals. Still, there isn’t an official recommendation for normal pre-meal blood sugar ranges in non-diabetic individuals.

After eating, people with diabetes should have a blood sugar less than 180 mg/dL one to two hours after starting a meal, or less than 140 mg/dL two hours after a meal, depending on the standards being used (ADA vs. AACE). People without diabetes should have blood sugar less than 140 mg/dL two hours after a meal.

If blood sugar levels are high before eating, it could be a sign of underlying insulin resistance, or a need to increase diabetes medications.

If the blood sugar levels are only high after eating, it can be indicative of a diet-related issue. Making diet changes can significantly help reduce postprandial (after eating) blood sugars. Some people take insulin before eating, so increasing the dose can help with high postprandial blood sugars as well.

Are high levels of blood sugar dangerous?

High blood sugar levels can be dangerous. Blood sugar above 200 mg/dL at any time is considered very high. In type 1 diabetes, very high blood sugar can lead to a life-threatening condition called diabetic ketoacidosis (DKA).

DKA occurs when insulin levels are very low, which causes the body to start producing ketones to use as fuel instead of glucose. A sign of ketone bodies being present is fruity-smelling breath.DKA can be fatal, so prompt medical attention is required.

Some symptoms of DKA include:

In type 2 diabetes, very high blood sugar can cause hyperglycemic hyperosmolar syndrome (HHS). HHS doesn’t cause ketones to build up, but it does present as:

  • Very high blood sugar

  • Dehydration

  • Decreased alertness 

Over time, high blood sugar does damage to the arteries and vessels of the body. When these vessels are damaged, complications can occur. Some of the complications from chronic high blood sugar include:

  • Heart (cardiovascular) disease: people with diabetes are two to four times more likely to die from cardiovascular disease than those without diabetes. People with diabetes are also more likely to have high blood pressure, which is another risk factor for heart disease.

  • Stroke: Diabetes increases the risk of stroke, as well as increases mortality when a stroke occurs.

  • Kidney disease and failure: High blood sugar damages the kidneys and can lead to kidney disease. About one in four people with diabetes have kidney disease.

  • Poor wound healing leading to amputations: High blood sugar inhibits proper wound healing. Diabetes is thought to be the leading cause of leg amputations worldwide.

  • Neuropathy: Damage to the nerves, which can cause painful symptoms like numb and tingling legs and feet, as well as delayed stomach emptying from damage to the stomach’s nerves.

  • Retinopathy and blindness: Damage to the nerves in the eyes is called retinopathy, which can lead to blindness if not treated.

Are low blood sugar levels dangerous?

Low blood sugar is called hypoglycemia. Hypoglycemia occurs when blood sugar falls below 70 mg/dL. Low blood sugar is dangerous, as it can cause dizziness and fainting, which increases the risk of a fall. Prolonged periods of severe hypoglycemia can cause insulin shock. Insulin shock can be life-threatening and lead to coma and death if it’s not treated quickly.

The most common symptoms of hypoglycemia include:

  • Feeling shaky and/or dizzy

  • Sweating

  • Hunger

  • Feeling irritable or moody

  • Feeling anxious or nervous

  • Headache

If hypoglycemia isn’t treated, severe hypoglycemia can occur. Signs and symptoms of severe hypoglycemia include:

  • Clumsiness or jerky movements

  • Muscle weakness

  • Slurred speech or difficulty speaking

  • Blurry or double vision

  • Drowsiness

  • Confusion

  • Convulsions or seizures

  • Unconsciousness/fainting

  • Coma

  • Death

Recent studies have associated severe hypoglycemia as a risk factor for dementia, falls, fractures, and heart attacks. Elderly people are at higher risk of hypoglycemia-related fractures; thus, many healthcare providers are more lenient with blood sugar targets in older patients with diabetes.

People without diabetes can also develop hypoglycemia. Some people without diabetes produce too much insulin in response to eating, especially simple sugars like candy and juice.  Reactive hypoglycemia usually occurs within a few hours after eating and can happen very quickly in some cases.

Alcohol can cause an increase in insulin secretion as well as interferes with the liver’s ability to create sugar (gluconeogenesis), which can both cause hypoglycemia.

What can you do to manage your blood sugar levels?

There are many things people with and without diabetes can do to manage their blood sugar levels. Some healthy habits to keep blood sugar levels in a healthy range include:

Eating consistent, balanced meals:

When you eat a balance of carbohydrates, protein, and fat (otherwise known as the Plate Method), blood sugar tends to rise more slowly and not drop quickly. Foods rich in fiber help promote stable blood sugars, such as whole grains, fruits, vegetables, legumes, nuts, and seeds. 

Having a good source of protein with carbohydrates is also good for promoting healthy blood sugar levels. Some protein sources include meat, eggs, fish, dairy products, legumes, nuts, and seeds. Eating protein with carbohydrates can also help reduce reactive hypoglycemia in people without diabetes.

Exercise regularly:

Being active helps lower insulin resistance and blood sugars. Muscles take up sugar for energy, so doing a mix of cardiovascular exercise (like walking) and weight training (bodyweight exercises or lifting weights) is ideal. Increasing muscle mass can help reduce insulin resistance since muscle tissue takes up glucose regardless of how much insulin is present.

Take medications as prescribed:

For those with diabetes, it’s important to take diabetes medications as prescribed. Skipping doses, or taking more than prescribed, can be detrimental. Never adjust diabetes medications on your own; always consult with a healthcare provider.

Check blood sugar regularly:

People who regularly check their blood sugar tend to have better-controlled blood sugar overall. Checking blood sugar levels at home helps people become aware of their blood sugar trends. It can also help people identify how their lifestyle habits affect their blood sugar and make adjustments to achieve better blood sugar control.

Practice good sleep hygiene: 

Poor sleeping habits and shift work have been associated with an increased risk of developing type 2 diabetes. Lack of sleep or a disrupted circadian rhythm seems to interfere with the body’s insulin response, leading to insulin resistance. The National Sleep Foundation also recommends several things to improve sleep hygiene, such as:

  • Limiting daytime naps

  • Avoiding caffeine and other stimulants close to bedtime

  • Exercising during the day

  • Avoiding heavy, fatty or spicy foods close to bedtime

  • Being exposed to natural light during the day

  • Establishing a relaxing bedtime routine

  • Keeping the sleeping environment comfortable, e.g., temperature between 60-67 degrees, using white noise machines, etc.

Manage your stress:

Some studies have suggested a link between stress and the increased risk of developing type 2 diabetes. Stress stimulates our body’s fight or flight response, which can result in increased blood sugar levels and insulin resistance.

Stress can also lead to poor eating habits, low-quality sleep, and other aspects of reduced self-care, which can also contribute to diabetes risk. Finding ways to manage stress can help improve both mental and physical health.

Watch your weight:

Being at a higher weight (“overweight” or “obese” according to body mass index) is associated with an increased risk of type 2 diabetes. Studies have found that a 5% reduction in body weight in those considered overweight or obese significantly reduced their risk of developing type 2 diabetes. Losing weight can also help reduce blood sugar levels in people with existing diabetes.

Why are good blood sugar levels important?

Healthy blood sugar levels are important for overall health. When blood sugar is high, it does damage to the entire body.

The longer the duration of high blood sugar (chronic high blood sugar or diabetes), the higher risk of developing complications. This is why managing blood sugar in people with diabetes is the biggest goal. Low blood sugar is also dangerous.

Maintaining healthy blood sugar levels can help reduce the risk of developing diabetes later in life. People at increased risk of diabetes should be especially mindful of their blood sugar trends and get screened for prediabetes and diabetes regularly. Risk factors for type 2 diabetes include:


Blood sugar levels are largely influenced by the hormone insulin. Disruptions in how the body produces and/or reacts to insulin can lead to blood sugar problems. Blood sugar levels that are both too high and too low can cause health problems and can be fatal in serious cases.

High blood sugar is called hyperglycemia, and low blood sugar is called hypoglycemia, and both can be dangerous. The optimal blood sugar level falls between those two extremes, generally between 70 and around 130 mg/dL.

People with diabetes can promote healthy blood sugar levels by taking medications as prescribed, checking blood sugar regularly, and practicing healthy lifestyle habits, such as eating a healthy diet and being active.

People without diabetes can promote healthy blood sugar levels by practicing healthy lifestyle habits such as healthy eating, being active, and reducing controllable risk factors for diabetes, like stopping smoking and practicing good sleep hygiene.

Periodically getting screened for blood sugar problems at preventative healthcare visits is also important since more than 1 in 3 Americans have prediabetes, which significantly increases the risk of developing type 2 diabetes.


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  2. https://www.pcori.org/research-results/2013/does-daily-self-monitoring-blood-sugar-levels-improve-blood-sugar-control-and
  3. Freckmann G, Hagenlocher S, Baumstark A, et al. Continuous glucose profiles in healthy subjects under everyday life conditions and after different meals. J Diabetes Sci Technol. 2007;1(5):695‐703. doi:10.1177/193229680700100513
  4. https://care.diabetesjournals.org/content/24/12/2023
  5. https://www.diabetes.org/diabetes/medication-management/blood-glucose-testing-and-control/checking-your-blood-glucose
  6. https://www.niddk.nih.gov/health-information/diabetes/overview/preventing-type-2-diabetes/game-plan


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