Design: Observational intensive longitudinal study, 14 days of blinded CGM with ecological momentary assessment six times daily
Population: 161 adults with type 1 diabetes, mean age 41.1 years, 55% female, 41% Hispanic
Primary outcome: Within-person association of time in guideline range versus time in personal range with same-day symptoms, functioning and diabetes-specific outcomes
Effect: Personal range more consistently associated with pain, fatigue, activity demands and perceptual speed; guideline range more strongly associated with diabetes distress and self-care; personal range explained unique variance beyond guideline range for several outcomes

Adults with type 1 diabetes wore blinded continuous glucose monitoring (CGM) for 14 days while answering prompts about symptoms and doing brief cognitive tests six times a day. For each three-hour window the investigators calculated both time in the guideline range of 70-180 mg/dL and time in a personal range defined as that person's own mean glucose plus or minus 50 mg/dL, then asked which one lined up better with how the day was actually going.

They came apart. Time in personal range was more consistently associated with lower pain and fatigue, better ability to meet the demands of an activity, and faster perceptual speed. Time in guideline range was more strongly associated with the diabetes-specific measures — less distress, better self-care. In models carrying both, the personal range explained variance the guideline range did not. The pattern was stronger in people already using their own unblinded CGM.

The practical reading is about habituation. Someone running high for years may feel genuinely unwell at 120 mg/dL, and that is a physiological account rather than an excuse. It argues for moving a target in steps and saying out loud that the first few weeks will feel worse before they feel better — and for not treating a good guideline number as proof the person is doing well, or a poor one as proof they are not trying.

Ask what glucose the patient usually sits at before showing them the download
Ask which number makes them feel bad, and at what level they feel normal
Where the gap to 70-180 mg/dL is wide, agree an interim target rather than the guideline one
Warn explicitly that early days at a lower range often feel worse
Record symptoms — pain, fatigue, ability to get through a shift — alongside the CGM metrics

Why it matters

A patient who says they feel worse at target may be describing something physiological, not resisting the advice.

The statistics, in plain English

These are within-person associations across a fortnight, not a trial of two targets. The study cannot say that adopting a personal range improves anything; it says the guideline metric misses part of what the patient is reporting. No hard outcome — HbA1c, complications, hypoglycaemia — was measured against the two metrics, so this belongs in how you talk about a number, not in what you aim for.