In one sentence
The share of your readings between 3.9 and 7.8 mmol/L (70 to 140 mg/dL), the band that moves for people without diabetes and the one VT's month-to-month comparison leans on.
Why it matters
It is the standard range's answer to the ceiling problem. In 153 healthy people wearing research sensors, the median share of the day between 3.9 and 7.8 was 96 percent, with the middle half of people between 93 and 98 (Shah 2019): a band with room to move in both directions, so that a late-eating fortnight or a run of short nights shows up as a few points lost, and a quieter month as a few gained. The 7.8 line is the two-hour post-meal figure that diagnostic testing has long used as its boundary, and the tighter band has since been adopted beside the standard range in the consensus on reporting sensor metrics in clinical studies (Battelino 2023).
What moves it
Downward: meal size and composition, late meals (Gu 2020), short sleep (Donga 2010), being unwell, the luteal phase, and a week of travel. The direction of your own month-on-month change is the reading; the level sits where it sits.
How to measure it well
As for every period figure: high coverage, the same sensor site, and periods of equal length. Read it with time above 7.8 in minutes, which is the same information in a unit that is easier to picture.
How Vitality Tracker uses it
Calculated for the day and the period, shown with the healthy-adult reference beside it and labeled as the study's figure; the Baseline Month's value is the reference for later months. It is not a Vitality Score input; the score reads the mean.
How far to trust the number
Calculated from measured readings; a point or two of change between periods is within the noise of a sensor, five is not.
Sources
- Shah VN, et al. J Clin Endocrinol Metab 2019;104:4356–64. doi:10.1210/jc.2018-02763
- Battelino T, et al. Continuous glucose monitoring and metrics for clinical trials: an international consensus statement. Lancet Diabetes Endocrinol 2023;11:42–57. doi:10.1016/S2213-8587(22)00319-900319-9>)
- Gu C, et al. J Clin Endocrinol Metab 2020;105:2789–802. doi:10.1210/clinem/dgaa354
- Donga E, et al. J Clin Endocrinol Metab 2010;95:2963–8. doi:10.1210/jc.2009-2430.