What is fasting blood glucose and which values are normal?
Fasting blood glucose is the glucose level in your blood after at least eight hours without food, usually measured in the morning. It serves as a baseline for sugar regulation. Normal values are usually below 100 mg/dL (5.6 mmol/L); a repeated value of 126 mg/dL (7.0 mmol/L) or more raises suspicion of diabetes.
Fasting blood glucose explained simply
After a meal, blood sugar (glucose) rises and the hormone insulin brings it back down. After a longer break without calories, at least eight hours, the system has settled. The value measured then is the fasting blood glucose. It shows how well your body keeps sugar in balance even without food intake.
Important: values depend on the laboratory and the measuring method, and a diagnosis is always made by a doctor, usually based on several measurements.
Typical classification of fasting blood glucose
Common reference values for adults, measured in plasma. Classification is always done by a doctor.
| Range | mg/dL | mmol/L |
|---|---|---|
| Range Normal | mg/dL below 100 | mmol/L below 5.6 |
| Range Elevated (impaired fasting glucose) | mg/dL 100 to 125 | mmol/L 5.6 to 6.9 |
| Range Suspected diabetes | mg/dL 126 or more, repeated | mmol/L 7.0 or more, repeated |
Fasting blood glucose in curcumin studies
Fasting blood glucose is a frequent target value in metabolic studies. Meta-analyses of randomised trials report only small average reductions in fasting blood glucose with curcumin, including in people with type 2 diabetes.
These are small changes. They show a trend in pooled data but are no substitute for treatment. The studies differ in dose, duration and preparation, and meta-analysis results are only as good as the individual trials. For the basics see meta-analysis and evidence.
Besides blood sugar, such studies also looked at blood fats such as triglycerides.
What influences the value
Fasting blood glucose varies with sleep, stress, illness, exercise and the previous evening's meal. A single raised value therefore does not necessarily indicate disease but should be checked by a doctor. The HbA1c value, which reflects the average of the past two to three months, is often used as a complement.
In studies, these factors are not always controlled in the same way, which is one reason why results can differ.
Frequently asked questions
How do I measure fasting blood glucose? At the doctor's from venous blood, or at home with a meter from a fingertip sample, after at least eight hours without food. Coffee with sugar or juice already counts as food.
What is prediabetes? A state with raised but not yet diabetic values. Lifestyle changes work well here.
Does curcumin lower blood sugar? Meta-analyses show small changes; the evidence is inconsistent.
If you take glucose-lowering medication or insulin, do not change anything on your own, and talk to your doctor before taking curcumin supplements. An additional glucose-lowering effect could influence your medication dose. This is not medical advice.
