Changes to BG at altitude

Sorry, a very quick post, scrabbled together from some other times I posted on the subject.

  1. When your body adjusts to higher altitudes, it has to cope with the lower oxygen levels that are at higher altitudes. This can cause the body to release the stress hormone cortisol, which helps your body cope with the lower oxygen levels. Stress hormones can cause a rise in blood sugar levels. Cortisol increases blood sugar through gluconeogenesis.

  2. The opposite effect is that at higher altitudes our hearts beat faster, which can lead to more rapid absorption of insulin and also burns more carbs. That could lead to a low.

  3. Many glucose meters use a glucose oxygenase method, which is dependent on oxygen in the surrounding environment. At higher altitudes, glucose meters can start to trend low. The higher you go in elevation, the greater the degree by which they are falsely low.


How do you do this? Amazing.

The glucose meter seemed to function well (Freestyle Lite). (I actually read a number of other people’s blog posts on different websites about the CGM malfunctioning, and their freestyle meter working properly).

We figured there was a cortisol component to the BG swings that were happening. The irony of stress is that it changes the BG, and then more stress happens when thinking about the bad blood sugar management!

Here’s a snapshot of what 24 hours at altitude looked like. EH had done a run (5.5mi/11 min a mile/8,000ft) Friday afternoon, but no running Saturday. Just wild BG after a fairly low carb Saturday (breakfast: eggs and spinach scramble; lunch: meat, cheese, snap peas; dinner: plain pork chop, 1 cob corn.) Dinner required 12u of insulin over 8 hours to cover the spike (normal injection to cover the corn? 2u.)

So, we are looking forward to some more average blood sugars now that we are home at sea level! And I’m not looking forward to our next visit to family in Denver as far as BG goes. Certainly felt like a wild card.


@TravelingOn, your published BG curve excited my curiosity.

While there is limited literature on altitude and glucose monitoring, I found almost no scientific research on altitude and BG, which is somewhat shocking.

So I went and did some statistical analysis of anecdotal evidence reported by PWDs and CWDs. In my first cursory review, I found more than 50 reports of change in BG with altitude.

The large majority (close to 80%) reported higher BG when moving to a location at higher altitude, sometimes much higher. A number if reports mention upping basal by 20% or spending significant time at 200 or even 300.

A small minority reported many, deep or sustained lows in the same circumstances.

A few reports mentioned BG stabilizing after 2 to 3 days.

I can see that some of these reports might be influenced by the following factors:

  • Lower hydration at altitude

  • Higher level of activity if on vacation and doing outdoor activities, also possibly resulting in lower hydration

  • Change in daily routine due to change in location

  • The worrisome effect of defective BG readings at altitude, reported for several glucose meters, but not for CGMs. I have not found studies on Dexcom and altitude yet, btw.

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Interesting. I live at 6600. I did the Pikes Peak Ascent/Marathon (up to 14k) and fingerstabbed every 30min and didn’t have any unexpected values. I’d get a little low (high 70’s) near the top but that’s because its hard to eat above tree-line. Otherwise 85-115…

I will be traveling to sea level for a few days next month and I wonder if I’ll see any differences. Hopefully not too extreme since occasionally I’ll travel for a sea level race I care about where its important that I have good numbers. I have a dexcom now.


Wow! This is great info! And it makes me feel better, because I was googling while in Denver, and couldn’t really find anything that clearly pointed in one direction. It was one of those YDMV moments for sure.

As far as your observations, which seemed like a good roundup…We were very aggressive about hydrating, as many people mentioned that altitude is dehydrating, so we went out of our way to drink lots of water (we do this at sea-level too, but not as much volume). Your other points make sense for shifting BG stats - vacation and travel makes for obvious changes in carb intake, routine, exercise (especially for more sedentary folks not like @CarolynA and @EricH who are exercising regulars) and so on.

For us, on the trip in question, we were almost the same as at home I would say, because we stayed with Eric’s brother and family who have similar patterns in eating and activity levels - the one difference being less sleep gotten. Eric did eventually cut back on running because he was feeling so crummy due to the highs.

For some reason it seems as if there is scant information on average people T1D being at high altitude. I did come across many things online that pointed out the similarities of Acute Mountain Sickness (AMC) and hypoglycemia. I also came across this article which is very interesting (I can’t get it to do that cool preview thing for some reason. Maybe you can fix it?)

(PS if that guy isn’t on FUD, I want to invite him! He sounds like a badass.)

Anyhow, that write up makes it seem as if his CGM functioned continually at both extreme altitudes and insane temps, and I read a couple of other user accounts that cited CGM functionality when the standard meters didn’t work.

@CarolynA, I wonder if your experiences have to do with living at a high altitude? I have heard anecdotes from friends that you do adjust to living higher, and things level out. I will look forward to hearing about your experiences as you head down to sea level and back up again.


+1 interest in hearing about your experience as you shift down to sea level.

But then again if you do end up high or low then elevation would probably only be one factor and food/sleep/exercise etc might confuse the result (experiments with 1 data point are kind of sketchy).

Anyway I’m still interested. :slight_smile:


So it really left altitude (and ?) as the primary difference in your case.

How long did you stay? Some people mentioned acclimation after 3-8 days.

I’m also interested in how to monitor/manage in the COLD as that guy described in the article. I’ll be hiking all night in Wisconsin in January- -15F windchill is expected. Hopefully the dexcom will work but it will be extreme enough (about 20 hours continuous exercise or more depending on snow level) that I will need data regularly. Don’t ask


@CarolynA, you should consider staging before or after (or both) here at our house if you are near at all. Check how close you will be to Oconomowoc, WI.

We might also come and cheer you up when you get close to the arrival line if you are not too far!


@EricH was there Thursday night through Sunday afternoon. We had wondered if acclimatization would occur if we remained longer.

@CarolynA I came across a couple of people’s stories while reading recently, and one of them mentioned that he switched to wearing bibs in the snow to keep his pump and infusion set warm enough to function. And another mentioned batteries not functioning at low temps. If you were doing MDI, it would seem as if the interior pockets on baselayers would be a good place to store the insulin so it didn’t freeze. There have been a couple of at home trials folks here on FUD have done on freezing insulin and overheated insulin you might like to read, as well as one on traveling with insulin.

Sounds like you’re having tons of fun adventures! Very exciting!


The race is called the Frozen Otter and starts end at Mauthe Lake Campground (route is ice age trail up to P down to H then back up to start/finish). I’m originally from Rockford, IL and have family near West Bend. Depending on snow levels and temperature, I might just do 50k. I will have a SPOT tracker… I would love to meet up before or after depending on my family and friends’ plans (my dad and one of his friends are planning on 50k). Oconomowoc is on the way to Rockford. I have no idea what my travel plans are at this point or how much extra time I’ll have, but I will probably plan to have my own car for flexibility anyway.


This is really close, not even an hour drive :slight_smile:

West Bend is closer to Mauthe Lake, so it might make more sense for you to stage from there. But if you want to stage from our house you are welcome. That also applies to your dad and friend, we have lots of space. I’ll send you our contact info.

If you have nothing better to do, we’d love to! But your family comes first.

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