Screening & monitoring · not graded
Continuous Glucose Monitor (CGM)
What the evidence looks at: glycemic variability metrics (surrogate); no hard-outcome RCT Randomized controlled trial: people are assigned to the treatment or a comparison by chance, so the groups differ only in what they received. It is the design that can show cause and effect. in non-diabetics.
At a glance
Wearable device · Metabolic health
A CGM measures interstitial glucose every 1 to 15 minutes, continuously, for 10 to 14 days. For longevity purposes the value is not glucose monitoring per se but the glycemic variability data it reveals: postprandial spikes, nocturnal glucose patterns, and meal-to-meal variation that fasting glucose and HbA1c A blood test that reflects average blood sugar over the previous two to three months. completely miss. Multiple human RCTs in non-diabetic adults demonstrate that CGM-guided dietary feedback reduces glycemic variability and improves metabolic markers.
| Leading options | Abbott FreeStyle Libre 3 (OTC in US since 2023). Dexcom Stelo (OTC). Previously prescription-only; now available without Rx for most adults. |
| What it measures | Interstitial glucose every 1 to 15 minutes. Trend arrows showing direction and rate of change. Time in range, glycemic variability index, mean glucose, estimated HbA1c. |
| Cost | $50 to $130 per 14-day sensor. No prescription required for Libre 3 and Stelo. Levels Health and Nutrisense offer subscription programs with app-based coaching at $200 to $400/month. |
| Wear duration | 10 to 14 days per sensor, then replace. Most users do 1 to 3 sensors to establish a baseline pattern. |
| Target ranges (non-diabetic) | Mean glucose below 100 mg/dL. Time in range (70-140 mg/dL) above 90%. Postprandial peak below 140 mg/dL. Glycemic variability (CV) below 36%. |
| Accuracy note | CGM measures interstitial fluid glucose, which lags blood glucose by 5 to 15 minutes. Not equivalent to fingerstick blood glucose for clinical decisions. |
Mean glucose trend, time in range (70-140 mg/dL), glycemic variability coefficient of variation (CV, target below 36%), postprandial peak responses to specific meals, nocturnal glucose stability. Its value is the comparison against baseline after dietary or exercise changes.
Why this letter
Continuous glucose monitoring in 57 adults, most without diabetes. Some people classed as normal by standard tests reached glucose levels in the prediabetic range 15 percent of the time and the diabetic range 2 percent of the time, and responses to identical meals varied between people. An observational study: it describes patterns and does not show that acting on them changes any health outcome.
For EBL Clinical practitioners: CGM is the most informative single-use diagnostic for identifying occult glycemic dysfunction in patients who appear metabolically normal by standard labs. One or two 14-day wear periods establish a baseline. CGM data feeds directly into EBL's Medication and Supplement Check outputs for insulin resistance and metabolic health conditions.
Dose, form and timing
Safety
CGM is generally very safe. Local skin reactions at the sensor site (redness, irritation) are the most common side effect. Sensor adhesive allergy occurs in some users. Manufacturers direct that sensors be removed before MRI, CT or diathermy. The Libre 3 and Stelo do not require fingerstick calibration.
Acetaminophen (Tylenol) at high doses can interfere with certain CGM sensors and falsely elevate readings. Ascorbic acid (vitamin C) at high doses can similarly interfere. Medications that affect glucose metabolism (corticosteroids, some antipsychotics, thiazide diuretics) will affect CGM readings, which is clinically useful information.
EBL does not verify the regulatory status of any device. Many consumer wellness devices are not FDA-cleared The FDA found a device substantially equivalent to one already on the market. Clearance is not approval and does not require trials showing benefit., and FDA clearance, where it exists, applies only to specific indications. The grade on this page describes the strength of published human trial evidence in the populations studied. It is not a recommendation for any individual and is not medical advice. Using any device for a health purpose is a decision for your physician.
Sources
Primary evidenceOne paper, linked to its PubMed record.
CGM in non-diabetic/longevity use is graded C: the glycemic-variability patterns it reveals are real (Hall et al. 2018, PLoS Biology; PMID 30040822, n=57, observational, NOT the 'Nature Medicine, n=1,000' the old page cited), but no RCT shows that CGM-guided changes in non-diabetics improve a hard outcome. Corrects the prior page's non-existent 'Ajala 2019' RCT citation.
Disclosure
Educational use only · Not medical advice · Starting, stopping or changing any supplement or medication is a decision for your physician
These statements have not been evaluated by the Food and Drug Administration. Any grade on this page describes the strength of published human trial evidence in the populations studied. It is not a recommendation for any individual and is not medical advice. Starting, stopping or changing any supplement or medication is a decision for your physician.
Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →