In one sentence
What research sensors recorded on people without diabetes, which is the only honest answer to "is my number normal": a set of published reference points, with their spread, from the studies that measured them.
The reference study
In the largest study with a current-generation sensor, 153 healthy people without diabetes, aged 7 to 80 and not obese, wore a blinded Dexcom G6 for up to ten days across twelve centers. Their mean glucose was 5.4 to 5.5 mmol/L (98 to 99 mg/dL) in every age group except the over-sixties, where it was 5.8. The median share of the day between 3.9 and 7.8 mmol/L was 96 percent, with the middle half of participants between 93 and 98. The within-person coefficient of variation averaged 17 percent. Time above 7.8 was a median 2.1 percent of the day, about 30 minutes; time below 3.9 a median 1.1 percent, about 15 minutes (Shah 2019). Those are the numbers VT shows beside your own month, labeled as the study's.
What they do not say
They are medians and means of a group, and the group was healthy by the usual tests, not by any stricter standard. When Stanford researchers put sensors on 57 adults and looked at the shape of the day rather than its average, glucose in people classed as normal by standard measures spent about 15 percent of the time in the range used to define prediabetes and 2 percent in the diabetic range (Hall 2018). Two people with the same mean can have very different days. And the response to a given meal varies enormously between people: in 1,002 British adults, including identical twins, person-to-person variation in the glucose response to identical meals was 68 percent (Berry 2020). A reference point tells you where a population sat; your month tells you where you sit.
How Vitality Tracker uses it
As context only. Your summaries show the reference figures beside your own, with the source named, and nothing in VT scores you against them: the Vitality Score reads your mean glucose through its own curve, and the meal library compares your meals with your meals. VT never calls a day normal or abnormal; it marks a figure green when it meets the published consensus target, and colors the trace by fixed bands.
How far to trust the number
As far as a well-run study of 153 people on one sensor model goes: the figures are reliable as a picture of that group, and a different sensor or an older or heavier group would shift them by a few tenths.
Sources
- Shah VN, et al. Continuous glucose monitoring profiles in healthy nondiabetic participants: a multicenter prospective study. J Clin Endocrinol Metab 2019;104:4356–64. doi:10.1210/jc.2018-02763
- Hall H, et al. Glucotypes reveal new patterns of glucose dysregulation. PLoS Biol 2018;16:e2005143. doi:10.1371/journal.pbio.2005143
- Berry SE, et al. Human postprandial responses to food and potential for precision nutrition. Nat Med 2020;26:964–73. doi:10.1038/s41591-020-0934-0.