In one sentence
How many minutes a day your glucose spent above 7.8, above 10.0, and below 3.9 mmol/L, and, as a softer line of VT's own, above 5.6.
Why minutes
Percentages read badly near a ceiling: 2.1 percent of a day sounds like nothing, and it is 30 minutes. In 153 healthy people, time above 7.8 was a median of about 30 minutes a day and time below 3.9 about 15 (Shah 2019), and both are easier to picture as minutes than as decimals. The diabetes-care consensus sets its own targets in this unit's percentage form (for most adults with diabetes, under 25 percent above 10.0, under 4 percent below 3.9 and under 1 percent below 3.0; Battelino 2019); those are reported here as what they are, the clinical standard, not a scale for the reader.
Why 5.6 as well
The 7.8 and 10.0 lines are far above where a healthy adult sits for most of the day, so a month's change in eating can leave them untouched. VT also counts exposure above 5.6 mmol/L (100 mg/dL), the figure many laboratories print as the top of the fasting reference range and the one the American Diabetes Association uses as the floor of its impaired-fasting-glucose band (ADA 2024). As a daytime line it is deliberately soft: everyone crosses it after meals, and the quantity worth watching is how many minutes a day, month against month.
What moves it
Above: the same things as the mean, concentrated in the hours after meals. Below: alcohol in the evening, a long gap between meals, hard training, and, falsely, the night you lay on the sensor; most of a healthy person's minutes below 3.9 are nocturnal and some are artifacts (see the gotchas).
How Vitality Tracker uses it
Calculated per day and per period, shown as minutes with the four lines named. Not a Vitality Score input.
How far to trust the number
Calculated from measured readings; the minutes above the high lines are robust, the minutes below 3.9 are the least trustworthy figure on the shelf, because a sensor's lows are where lag and compression do their work.
Sources
- Shah VN, et al. J Clin Endocrinol Metab 2019;104:4356–64. doi:10.1210/jc.2018-02763
- Battelino T, et al. Diabetes Care 2019;42:1593–603. doi:10.2337/dci19-0028
- American Diabetes Association. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes 2024. Diabetes Care 2024;47(Suppl 1):S20–42. doi:10.2337/dc24-S002
- Vitality Tracker, Knowledge Base brief, catalogue D.