Normal Blood Sugar Levels for Adults Without Diabetes
For an average adult without any underlying medical conditions, normal blood sugar is defined as a fasting blood glucose level of less than 100 mg/dL (5.6 mmol/L) and a random or post-meal blood glucose level of less than 140 mg/dL (7.8 mmol/L). 1
Fasting Blood Glucose (Normal Range)
- Fasting glucose should be less than 100 mg/dL (5.6 mmol/L) in individuals without diabetes 1
- Fasting measurements are typically taken after an overnight fast of at least 8 hours 2
- Fasting glucose levels between 100-125 mg/dL (5.6-6.9 mmol/L) indicate impaired fasting glucose, which is a prediabetic state and not considered normal 2
Post-Meal (Postprandial) Blood Glucose
- Random or post-meal glucose should be less than 140 mg/dL (7.8 mmol/L) in individuals without diabetes 1
- This measurement can be taken at any time, regardless of when the person last ate 1
- Post-meal glucose levels of 140-199 mg/dL on a 2-hour oral glucose tolerance test indicate impaired glucose tolerance, another prediabetic state 2
Optimal Range for Cardiovascular Health
- Research suggests the fasting glucose level associated with the lowest cardiovascular risk is in the range of 85-99 mg/dL 3
- Fasting glucose levels below 70 mg/dL may be associated with slightly increased stroke risk, though this is primarily relevant in specific populations 3
- Even within the "normal" range (below 100 mg/dL), higher fasting glucose levels (87 mg/dL or above) are associated with progressively increased risk of developing type 2 diabetes in young adults 4
Critical Thresholds to Recognize
- Hypoglycemia begins at less than 70 mg/dL (3.9 mmol/L), which triggers neuroendocrine responses even in people without diabetes 5, 1
- Diabetes is diagnosed when fasting glucose is 126 mg/dL or higher, or when 2-hour post-meal glucose is 180 mg/dL or higher 6
Important Clinical Context
The distinction between "normal" and "optimal" is clinically relevant. While less than 100 mg/dL is considered normal, research demonstrates that fasting glucose levels in the upper normal range (91-99 mg/dL) combined with other risk factors like elevated triglycerides or obesity significantly increase diabetes risk 4. This suggests that for long-term metabolic health, targeting the lower end of the normal range (85-99 mg/dL) may be preferable 3.