Blood sugar is the amount of glucose circulating in your blood. Glucose provides energy for your body, especially your brain and muscles. Your body carefully regulates glucose through hormones such as insulin and glucagon.
When blood sugar stays too high or too low, it can affect how you feel and may indicate an underlying health issue.
What Is Blood Sugar?
Blood sugar, also called blood glucose, mainly comes from the carbohydrates you eat. After digestion, glucose enters the bloodstream and can be used by cells for energy.
Insulin helps move glucose from the blood into cells. The liver can also store and release glucose depending on what your body needs.
What Are Normal Blood Sugar Levels?
For non-pregnant adults, commonly used fasting glucose categories are:
Fasting Blood Sugar General Category
Below 100 mg/dL Normal
100–125 mg/dL Prediabetes range
126 mg/dL or higher Diabetes range
A diagnosis should not usually be based on a single home glucose reading. Healthcare professionals may use laboratory testing and repeat measurements.
What Causes Blood Sugar to Rise?
Several factors can increase blood sugar, including:
Eating carbohydrate-rich meals
Stress
Poor sleep
Illness
Certain medications
Physical inactivity
Hormonal changes
Morning glucose can also be higher in some people because of normal hormonal changes known as the dawn phenomenon.
Can Blood Sugar Change During Fasting?
Yes. Fasting does not always mean glucose will continuously decrease.
During fasting, insulin levels generally fall while glucagon helps the liver release glucose. This allows the body to maintain an energy supply even when food is not being consumed.
Stress and cortisol can also influence glucose levels. Learn more about cortisol and fasting.
How Can You Support Healthy Blood Sugar?
Simple lifestyle habits can support healthy glucose regulation:
- Choose High-Fiber Foods
Fiber can slow digestion and the absorption of carbohydrates. Learn more about how fiber slows sugar absorption.
- Stay Physically Active
Regular physical activity can help muscles use glucose for energy and support insulin sensitivity.
- Get Enough Sleep
Sleep is an important part of metabolic health. Poor sleep can affect hormones and glucose regulation. Read more about how sleep affects blood sugar.
- Manage Stress
Long-term stress can influence hormones that affect glucose. Stress management, adequate sleep, and regular activity may support better metabolic health.
When Should You Talk to a Doctor?
If your glucose readings are repeatedly outside the expected range, or you have symptoms such as excessive thirst, frequent urination, unexplained weight changes, or unusual fatigue, discuss them with a healthcare professional.
People taking glucose-lowering medication should also avoid making medication changes without medical guidance.
Final Thoughts
Blood sugar is an important part of metabolic health. It naturally changes throughout the day depending on food, activity, sleep, stress, hormones, and other factors.
Understanding these influences can help you make sense of glucose readings rather than focusing on a single number.
