The first time I flew long-haul with my Type 1 diabetes, I thought I'd planned for everything.
I had my insulin, my CGM, my snacks, a letter from my GP. I'd checked the airport security rules and packed a carry-on I was frankly rather proud of.
What I hadn't planned for was the bit where none of it worked quite the way it does on the ground.
My blood glucose spent the first five hours doing something I couldn't explain. My CGM kept losing signal. The meal timing was off by three hours from anything I'd calculated. Somewhere over central Asia, I caught myself staring at my Free Style Libre with the particular combination of confusion and mild dread that every Type 1 knows well.
Long-haul flying with diabetes is its own discipline. Not impossible — I've now done it more times than I can count. But there are things nobody tells you until you're already thirty-five thousand feet up and learning them the hard way. This is the article I wish I'd had at the beginning.
Blood glucose behaves differently at altitude
This is the thing that surprises most people. You haven't eaten anything strange. You haven't miscalculated a dose. And yet your glucose is doing something unexpected.
Commercial aircraft cabins are pressurised to an altitude equivalent of roughly 6,000–8,000 feet — lower oxygen than at sea level.
A study published in the National Library of Medicine shows that reduced oxygen at altitude can affect how quickly insulin is absorbed and how the body uses glucose.
Stress hormones from the travel itself — even the low-grade kind — push things higher still. And then there's the inactivity: if you usually keep glucose stable through regular movement, sitting still for ten hours changes everything.
💡 What to do: check your blood sugar more frequently than usual, especially in the first two hours. Don't panic at unexpected readings — try to understand what's happening rather than over-correcting. If you're running higher and you've eaten nothing, the altitude and stress response may be the explanation before you reach for extra insulin.
The CGM problems nobody warns you about
CGMs are genuinely transformative for long-haul travel — being able to see your glucose trend on a fourteen-hour flight without finger-pricking every hour is a real quality of life improvement. But they have quirks at altitude worth knowing.
Reduced cabin pressure and humidity can affect adhesion. Sensors that stick perfectly in normal conditions can start to lift mid-flight. Carry extra adhesive patches.
Signal can also drop if your receiver is stowed in the overhead bin — keep it within range.
Abbott's FreeStyle Libre guidance notes the reader needs to be within 4cm of the sensor for scanning, easy to forget when you're trying to sleep on a long´haul flight. And know how your system handles flight mode before you board — not after.
👉 If you're flying with a CGM, our full guide to CGMs at airport security covers what the scanners actually do to your device, your rights at the airport checkpoint, and what Dexcom and FreeStyle Libre users need to know.
The insulin absorption issue (and why it matters more when flying)
Here's something I didn't fully understand for years: insulin absorption changes depending on where you inject, your body temperature, and your activity level. On a long-haul flight, all three are different from normal.
You're cooler and less active. If you've been sitting in the same position for four hours, the tissue at your injection site may have less blood flow than usual, slowing absorption and delaying the action of rapid-acting insulin.
This can make it look like your insulin isn't working — when actually it's just working more slowly. The temptation is to correct with more, which then all kicks in at once. I've done exactly this. It's not a pleasant experience at altitude.
💡What helps: a brief walk to the galley can help increase your insulin sensitivity during a flight. Avoid injecting into areas you've been sitting on for hours. If you're on a pump, basal rates that work on the ground may need adjustment — worth discussing with your diabetes team before you fly.
Keeping insulin cool at 35,000 feet
Your insulin must be in your carry-on. Always. The hold can reach sub-zero temperatures and freeze insulin solid. This isn't a precaution — it's essential.
Inside the cabin, the challenge is different. Aircraft are cold and dry, and insulin from a cold environment absorbs more slowly — let it warm slightly before injecting if you can. But airports are often much warmer than aircraft. If you're transiting through Dubai or Singapore, the time between your plane and the lounge can be enough to stress insulin that isn't properly protected. The cold chain has to hold across the full journey — not just at cruising altitude.
This is exactly why a proper insulin travel cooler matters for the whole trip, not just the flight itself.
👉 My guide on how to keep insulin cool when travelling covers every scenario where temperature becomes critical — from long-haul flights to beach days to hotel mini-fridges.
Airline food: the carb-counting lottery
💡A few strategies that genuinely help:
- Pre-order a diabetic meal if the airline offers one (British Airways does) — they tend to be lower in refined carbohydrates than the standard option.
- Carry your own reliably-carb-counted snacks so you're not dependent on the trolley if your glucose drops.
- Don't try to match airline meal timing to your usual bolus routine — adapt, estimate cautiously, and monitor closely afterwards.
- Tell the airline about your diabetes when you book, which can unlock priority boarding — useful when you need extra time to stow medical supplies.
The time zone problem: when does "basal" actually happen?
If you take long-acting insulin once a day, or use a pump with set basal rates, a flight crossing eight or ten time zones disrupts the entire framework your regime is built on.
Your "once-daily at 10pm" injection now falls somewhere mid-flight, several time zones from where it was working before.
👉 This deserves more space than I can give it here. My dedicated guide on managing insulin across time zones covers exactly this — with specific guidance on adjusting different insulin types and advice for eastward versus westward travel.
💡 The one thing I'll say here: work this out with your diabetes team before you fly. It's entirely solvable with advance planning and genuinely stressful to figure out mid-flight.
The diabetes paperwork that actually saves you
If flying internationally (especially outside of Europe), you may need documentation — not usually for airport security, but for carrying needles, pens, and liquid medication through multiple airports and border controls. At minimum:
- A diabetes travel letter from your GP, confirming your diagnosis, medications, doses, and the need to carry insulin and supplies. This is what security officers actually want to see.
- Copies of your prescriptions — especially if you're carrying larger quantities across international borders.
- Your travel insurance documents, with the 24-hour emergency number accessible. Not buried in your email.
👉 We've put together a free downloadable diabetes travel letter template — along with a full guide on what it needs to include, what to ask your GP for, and why a generic letter often isn't enough.
And on travell insurance: standard policies typically exclude pre-existing conditions — on a long-haul trip to the US or Australia, a hospital visit without proper cover can cost tens of thousands of pounds. Everything you need to know about travel insurance for diabetics in the UK is here.
What goes in the carry-on (and what goes in your pocket)
Everything diabetes goes in your carry-on. No exceptions.
But the things you'll need in the first hour — fast-acting glucose, one insulin pen, your CGM reader — go in your personal item or seat pocket. Because the overhead bin will be full, you'll be in a middle seat, and the seatbelt sign will be on.
💡My list: fast-acting glucose in my pocket before boarding, insulin pens with one in the seat pocket, insulin travel cooler, CGM spares (sensors, adhesive patches, charger), ketone testing strips, a Baqsimi nasal glucagon kit, carb-counted snacks, and medical documents in a dedicated pocket. Always twice the insulin you think you'll need — delays happen, luggage gets lost, and the pharmacy at your destination may not stock your brand.
👉 For everything that goes into preparing for the full trip with diabetes — not just the flight — our complete guide to travelling with diabetes covers it all in one place.
The bit nobody writes about
Long-haul flying with diabetes is tiring in a way that goes beyond the physical. You're managing something complex, continuously, in an environment you can't control — unpredictable food, disrupted sleep, no ability to move freely.
The emotional weight of living with diabetes is real, and travel puts it under particular pressure.
What I've found, after many years and many long-haul flights, is that the anxiety diminishes in proportion to how well you've prepared.
Not because everything goes perfectly — it doesn't, not always. But because when something goes unexpectedly, preparation means you have options. And options feel like control. That's what all of this is really about. Shrinking the space where the unexpected becomes the catastrophic. And then getting on the plane, and going.
💬 We'd Love To Hear From You!
Have you had a long-haul flight that taught you something about managing diabetes in the air? A trick that transformed your experience, or a mistake you'll never make again?
Share it in the comments below — this community is better for every honest story!
