In one sentence
The share of your readings between 3.9 and 10.0 mmol/L (70 to 180 mg/dL), the range that diabetes care uses as its standard, reported because every sensor app reports it.
Where the range comes from
It is the international consensus range for people with diabetes, agreed by an expert panel in 2019 so that clinics and patients could work toward the same numbers; the panel's recommended target for most adults with type 1 or type 2 diabetes is more than 70 percent of readings in this range (Battelino 2019). The bounds are clinical: 3.9 is where hypoglycemia symptoms begin to matter, 10.0 is a treatment threshold. Neither was chosen with healthy adults in mind.
Why it says little for most readers
A healthy adult's sensor spends almost the whole day inside 3.9 to 10.0: in 153 people without diabetes, the median time above even the tighter 7.8 line was 2.1 percent of the day (Shah 2019), so time in the standard range runs close to 100 percent and barely moves from week to week. That is why VT also shows the tighter band, which is the one that moves for people without diabetes, and why it reports exposure as minutes rather than percentages, which read better near the ceiling.
What moves it
Downward: large meals, late meals, sleep loss, being unwell, the second half of the menstrual cycle, and, falsely, compression lows at night (see the gotchas). Upward: not much beyond being well and eating moderately; it is near its ceiling already.
How Vitality Tracker uses it
Calculated for the day and the period and shown beside the tighter band, with the consensus range named as diabetes care's standard. It is not a Vitality Score input.
How far to trust the number
Calculated from measured readings; its precision is the sensor's, and its usefulness for a person without diabetes is limited by the ceiling effect described above.
Sources
- Battelino T, et al. Clinical targets for continuous glucose monitoring data interpretation: recommendations from the International Consensus on Time in Range. Diabetes Care 2019;42:1593–603. doi:10.2337/dci19-0028
- Shah VN, et al. J Clin Endocrinol Metab 2019;104:4356–64. doi:10.1210/jc.2018-02763.