Adults living with type 1 diabetes

What this guide does, and what it does not

Adult type 1 diabetes is a long arc. Some readers arrive here in the first year of adult care, finding the rhythm of clinic letters and prescription requests that used to be done by a parent. Some arrive twenty years in, with a settled routine the body knows and a CGM pattern the partner could draw from memory. The chapters that follow do not try to cover every adult year; they split the work the way the years actually split it.

What this guide does is name the foundations that hold across the decades, then map the levers that shift inside two readable windows: the work of the younger adult who is consolidating those foundations in their own household, and the work of the adult between thirty and sixty-five whose life events keep moving insulin sensitivity in named directions. What this guide does not do is hand you a number to take this evening. Every figure on these pages is a population-average reference at your total daily dose, not a personal dose; the dose conversation is with your care team.

The reader who wants the older-adult arc (65 and above) will find the next guide in the cluster more useful; the reader who wants the female arc at any life stage will find the female guide more useful; the reader supporting a child with T1D will find the children and young people guide more useful. Each cross-hub bridge sits at the foot of this hub and at the foot of each part.

How the years split the work

The honest answer is that the years do not split cleanly. The body does not change shape on a birthday. The pattern that does hold across the adult conversations in clinic is that the work of the twenties is the work of moving the foundations into your own household, and the work of the thirty-to-sixty-fives is the work of recognising the life events that keep moving the levers. The two parts that follow split that work in a way the reader can actually navigate.

The reader who wants the foundations primer reads Part 1 first. The reader who wants the life-event arc reads Part 2 first. The order of the two parts is set by where you are, not by the number on the kicker.

The shared foundations that carry across the years

Across the adult conversations I have in clinic, the same six foundations come up before any device-specific question, any settings change, any algorithm option. They are the ground the rest of the work sits on. Naming them in one place at the front of this guide saves restating them three times across the parts that follow.

Total daily dose is the first foundation. It is the single number you can quote in any clinic room in any country, and the number every other adult-band rule of thumb in this guide is anchored to. If you do not know your TDD, the seven-day average from your pump or pen report is the figure to bring to the next review. Insulin-to-carb ratio is the second foundation, and the lever the algorithm leans on most heavily; the AID literature is consistent that ICR carries more of the algorithm’s day-to-day work than the target dial does (ADA 2026 §7). Insulin sensitivity factor is the third foundation, and the lever that catches the high reading rather than the meal; on AID it carries the correction work the algorithm runs in the background.

IOB visibility is the fourth foundation. Knowing what is still on board from the last bolus or the last algorithm-driven micro-bolus is what keeps the next correction sane. The IOB part of the device-foundations cluster goes deeper into how each AID system makes its IOB readable. Hypo recognition is the fifth, and the foundation that the adult years quietly erode for many readers as exposure to lows builds impaired-awareness (Cryer 2013); rehearsing the signs with someone in the household helps. Hypo treatment is the sixth, and the foundation where the population-average adult anchor sits at 15 g fast-acting carbohydrate, recheck at fifteen minutes, repeat if still low; weight-led paediatric figures do not apply in the adult band, and your team will set the personal number.

The Foundations cluster on GNL holds each of these six as its own page; the parts of this guide cross-link in rather than restate. The reader who wants the deep dive opens the cluster; the reader who wants the adult-band map keeps reading.