What insulin actually does
The one idea that makes everything else make sense, whether you were diagnosed last week or eight years ago and never quite got it explained.
Insulin is the key that lets glucose (sugar) leave your blood and get into your cells for energy. In type 1, your body has stopped making it, so you add it back, a slow background amount all day (basal), and quick top-ups for food (bolus). When there’s not enough insulin, glucose builds up in the blood and can’t be used. That’s the whole job: insulin moves glucose out of the blood and into the body.
Glucose needs a key to get in
Everything you eat that contains carbohydrate becomes glucose in your blood. Your cells run on that glucose, but they can’t absorb it on their own. Insulin is the signal that unlocks them. Your liver also releases stored glucose between meals and overnight, which is why you need insulin even when you’re not eating.
It's not the same for everyone, or every day
How much insulin someone needs, and how fast it works, changes with a lot of things. This is normal, it’s not you doing it wrong.
What this looks like in practice
Examples to show how insulin behaves, not instructions or doses for you. Your own amounts are something only you and your team set.
A mealtime (bolus) dose covers the toast. If it's taken a little before eating, it has time to start working as the glucose arrives.
No food, but the liver still trickles out glucose, so the slow background (basal) insulin is what keeps things steady until morning.
Worth paying attention to
Questions that make an appointment useful
When it's urgent
Missing insulin, especially your basal, can let glucose and ketones climb, which can become DKA. If you have high glucose with ketones, are being sick and can’t keep fluids down, or feel very unwell: don’t stop your insulin, and contact your diabetes team or NHS 111. If you’re drowsy, confused or breathing fast, call 999.