Fasting insulin

How hard your body is working to keep blood sugar normal — it rises years before glucose does.

What it measures

The level of insulin in your blood after an overnight fast.

Why it matters

Fasting insulin often climbs long before glucose or HbA1c move, so a low-normal value is an early, sensitive sign of preserved insulin sensitivity — and a high one is an early warning even when glucose still looks fine.

Healthy target

< 6 mU/L

How to read your value

Assays vary between labs, so compare like with like and watch the trend. The longevity-optimal range sits below many standard lab cut-offs.

What can affect it

• Refined carbohydrate and overall calorie intake
• Body fat, especially around the middle
• Physical activity and muscle mass improve it
• Sleep and stress

Does the target differ by age or sex?

Same target for men and women — lab-to-lab assay differences matter far more than sex.

When to talk to a clinician

Interpret alongside glucose and HOMA-IR; discuss persistent high values as part of a metabolic review.