According to the CDC [1], more than 38 million people in the U.S. have diabetes [2], a condition that's linked with high levels of blood sugar. But doctors regularly check blood sugar levels during annual physical exams, whether you have diabetes or not, making this measurement something many people will need to try to decipher at some point. With that, it's fair to wonder what blood sugar level is considered dangerous and what falls into the normal range.

Why does this matter? Your blood sugar levels indicate how well your body is processing glucose [3], AKA sugar. "Glucose provides energy to the body and, in particular, to the brain for which it is the major energy source," says Christoph Buettner, MD, PhD. "If blood sugar is very low, our brain may be damaged."

High blood sugar is also a big concern. "High blood sugar may lead to long-term complications such as cardiovascular disease, kidney damage, nerve issues, and vision problems," Buettner says. "Hence, it's important to have blood sugar in a normal range — not too high and not too low."

Here's what you need to know about ideal blood sugar levels and how to keep your blood sugar steady throughout the day.

Experts Featured in This Article:

Christoph Buettner, MD, PhD, [4] is the chief of the division of endocrinology at Rutgers Robert Wood Johnson Medical School.

Louis J. Morledge, MD [5], is an internal medicine physician at NYU Langone Health.

Kathleen Bethin, MD, PhD [6], is a diabetes researcher and clinical professor of pediatrics in the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo.

What is a Normal Blood Sugar Level?

It's normal for blood sugar to fluctuate throughout the day, which is why when you test in relation to eating matters. There are a few numbers to consider when it comes to normal blood sugar levels, depending on the type of test you take. The American Diabetes Association [7] (ADA) breaks them down this way:

• Fasting (i.e. before eating): 70–100 mg/dL
• Two hours after eating: Less than 140 mg/dL. "After eating, blood sugar should stay below 140 if you are healthy," Buettner says. "In a lot of people that are on their way to develop prediabetes, it already goes higher."
• HbA1c (your average blood sugar level over 2–3 months): Below 5.7%

What are symptoms of high blood sugar and low blood sugar?

The symptoms of high and low blood sugar vary by person and the exact level of the blood sugar you're experiencing, says Louis J. Morledge, MD, internal medicine physician at NYU Langone Health. If blood sugar levels are a little high or a little low, people may not feel any different, he says. However, there are some distinct symptoms that are usually linked with high and low blood sugar.

High blood sugar signs

Also known as hyperglycemia, Morledge says high blood sugar can cause these symptoms:

• Excessive thirst
• Fatigue
• A general sick feeling
• Stomach pain
• Rapid breathing
• Headache

Low blood sugar signs

Also called hypoglycemia, low blood sugar can cause these symptoms, says to Kathleen Bethin, MD, PhD, a diabetes researcher and clinical professor of pediatrics in the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo.

• Sleepiness
• Shakiness
• Extreme hunger
• Crankiness
• Sweating
• Dizziness
• Paleness

What Blood Sugar Level is Considered Dangerous?

There are some blood sugar levels that are considered dangerous—no matter whether you have diabetes or not. (If you are in fact diabetic, check with your doctor to see what numbers and ranges they recommend you aim for.)

On the low end, a fasting blood sugar level of below 70 mg/dL is concerning, Buettner says. "Severe hypoglycemia —under 54 mg/dL—can lead to seizures, unconsciousness, or death as the brain depends on glucose as energy source," he says.

High blood sugar that's consistently above 180 mg/dL after meals or exceeding 300 mg/dL is also concerning, Buettner says. Having "extremely high levels" of 600 mg/dL can lead to complications known as diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS). These are medical emergencies, he cautions.

How to Maintain Healthy Blood Sugar Levels Throughout the Day

There are a few things doctors recommend that can help keep your blood sugar levels in a healthy range. This helps lower the risk of developing diabetes and can also help maintain stable energy, Morledge explains.

• Focus on whole, unprocessed foods. "Eat foods high in fiber [8], especially fresh fruits and vegetables," Bethin says. These foods tend to add bulk to your stomach when combined with liquid and digest more slowly, keeping your blood sugar consistent.
• Eat whole grains. These are better for blood sugar management than white breads, because they slow the absorption of food, lowering the risk of blood sugar spikes, Bethin says.
• Drink plenty of water. The National Academies' Institute of Medicine recommends [9]that men have about 15.5 cups of fluids a day, while women get about 11.5 cups (that's from both food and drink). Still, it's best to limit intake of simple sugars, such as juice and soda, Bethin says. These can lead to blood sugar spikes and crashes, throwing your levels out of whack. Instead, add lime or lemon to your water [10].
• Exercise regularly. "Exercise helps your body use insulin more effectively and keeps blood sugars stable," Bethin says. (Insulin is a hormone [11] that helps your body convert food into energy and regulates blood sugar levels, per the Cleveland Clinic.)
• Limit sugary foods. Sugary foods don't need to be villainized, but it is worth mentioning that eating too much of them over time can make it hard for your body to effectively regulate blood sugar, Morledge says. This can lead to a condition called insulin resistance, which occurs when the pancreas makes too much insulin to handle high blood sugar levels, Morledge says. Over time, that can lead to type 2 diabetes.
• Try to manage your stress. Stress doesn't get a lot of attention as it pertains to blood sugar management — but it should. Morledge points out that stress itself can increase blood sugar levels by causing the body to release hormones like cortisol and adrenaline, both of which make it harder for insulin to do its job.

Of course, if you've been diagnosed with diabetes, it's also important to consult with a doctor. They'll be able to offer personalized guidance on how best to manage your blood sugar. But, if you're healthy and your annual blood test shows your blood sugar levels are normal, this is one health metric that there's really no need to stress over.