What Is the Normal Range for Blood Sugar?

Checking blood sugar levels is an important screening that can help identify prediabetes. But what is considered “normal” blood sugar and what is too high? Glucose is a simple sugar that provides energy for the brain, muscles and the rest of the body’s cells. Nate Wood, MD, Director of Culinary Medicine at Yale School of Medicine and Irving and Alice Brown Teaching Kitchen at Yale New Haven Health says blood glucose is like “Goldilocks,” meaning we don’t want too much or too little. Instead, there’s a zone that’s “just right.”

Normal blood sugar v. high blood sugar

A blood glucose test is used to measure blood sugar, and it’s recommended everyone be screened for prediabetes and type 2 diabetes by age 35. Those with a family history of diabetes, symptoms or risk factors, or certain ethnic backgrounds may need to get checked sooner. 

Normal blood sugar would be 99 mg/dL or lower after a blood test in which the patient fasted overnight. A blood sugar of 100 mg/dL or higher is considered abnormal. A range of 100-125 mg/dL falls under the category of prediabetes, while a blood sugar of 126 mg/dL or higher is considered type 2 diabetes. At least two abnormal blood sugar test results are needed to make a diagnosis. Hemoglobin A1C, a marker of blood glucose over a three month period is also helpful to diagnose prediabetes and diabetes. 

“High blood sugar is very dangerous in the long-term. This is largely because it damages our blood vessels and nerves and can increase the risk of infection. Chronically high blood sugar levels can affect vision and lead to peripheral neuropathy, which is losing sensation in the feet and/or hands due to damaged nerves. Damaged blood vessels can increase the risk of heart attacks, strokes, and peripheral vascular disease,” said Dr. Wood.

What impacts blood sugar levels?

Insulin is a hormone released from the pancreas when we eat that moves glucose from blood to the body’s tissues and helps to deliver energy to our cells. Type 1 diabetes is a condition where the body does not make insulin, which can result in dangerously high blood sugar levels. Type 2 diabetes is different in that the body makes insulin, but the body becomes resistant to it, causing blood sugar levels to spike.

It’s not common for patients with prediabetes or type 2 diabetes to experience symptoms. However, symptoms of high blood sugar or hyperglycemia include excessive thirst, urinating frequently, fatigue, dry mouth, weight loss and blurry vision.

Patients with symptoms or any risk factors should contact their doctor to have their blood sugar levels evaluated. Prediabetes can be reversed, and certain medications as well as lifestyle modifications can help prevent the progression from prediabetes to diabetes.

“Individuals with prediabetes are at higher risk of developing diabetes,” said Northeast Medical Group Endocrinologist L. Priyanka Mahali, MD. “Several clinical conditions like high cholesterol levels, insulin resistance and obesity are commonly seen in individuals with prediabetes, which can put them at high risk of developing cardiac disease and fatty liver disease. Treatment of prediabetes with lifestyle changes or medications can prevent these complications.”

Some of those lifestyle modifications include quitting smoking, exercising, losing weight, getting better sleep, reducing stress and eating a healthy diet that incorporates fiber-rich fruits, vegetables and whole grains.

So, should everyone be monitoring their blood sugar throughout the day? Not quite, says Wood, as patients with normal blood sugar levels are not at risk of having their blood sugar go dangerously low or dangerously high. However, it is a good idea to avoid big blood sugar spikes. To do this, aim to minimize the amount of added sugar you consume and look for ways to add fiber throughout the day. For example, opt for whole-grain toast instead of white, add veggies to a sandwich at lunch, or choose a dessert with whole fruit after dinner.