Heat Question

Hi Everyone,

I’ve heard that higher temperatures result in more insulin needed…I was wondering how much this is the case if you’ve experienced it.


My experience has been just the opposite, higher temps cause less use. But most of that experience is in combo with yard work (mowing, cutting down/pruning trees/bushes, etc.) sometimes lite, sometimes involved. I went on a cruise and the higher heat in combo with just reading in a chair/lounge had no effect. Will be interesting to see what other responses you get…


With heat there are a few different factors at work. And those factors act counter to each other.

Needing less insulin:
When the temperature is hotter, your blood will circulate faster. More blood is directed to the skin to help cool you off. Those things will make insulin absorb faster.

If someone is on a pump, this would affect both basal and bolus insulin. If you are using injections, then it would apply more to the bolus insulin.
(Injected basal insulin like Lantus or Levemir or Tresiba have their delivery slowed by other factors besides absorption. So they might be affected somewhat, but only in a very small way.)

So pump users would generally see more insulin sensitivity (i.e.needing less insulin) from heat than those using MDI, because for a pump it will affect both basal and bolus.

Needing more insulin:
But in the case of reduced insulin sensitivity (i.e. needing more insulin), there is a different reason for that. When it is hot outside, your blood needs to circulate faster to keep you cool. And this makes your heart work harder. Your heart rate increases and you may also have more stress hormones released because your body feels that the hot temperature is a problem. If you sweat a lot and become dehydrated, your heart has to work even harder! If you lose a lot of electrolytes, even more stress.

Those things will cause your body to need more insulin instead of less insulin.

So there are 2 opposite affects from heat. And how they end up affecting our insulin needs depend on how hot it is, and how our body deals with hot temperatures, and how acclimated we are to the heat. And also if we are using a pump or MDI.


@Eric Great explanation, particularly that last bit about being acclimatized! When I was in 1st/2nd grade, my dad (Navy officer) was assigned to White Sands Missile Range, NM, so we lived in high desert on the base. We had recess with a jungle gym and a shade house (roof supported by columns) because temps would get up to 117. You could always tell the new kids: 1) they tried to use the jungle gym (metal, not advised in high temps); 2) they stayed in the shade house instead of running around like those that had “ acclimatized!” No T1 issues back then to test your advice with though…


This is my first summer as a T1D so I’m still working out my weather patterns.

I’m on MDI and it’s been 30C+ here in Europe the last week (mostly in the 90sF, a few days over 100F).

Earlier this week, I definitely noticed insulin resistance and needed 150% my normal insulin at most meals. That seemed to end yesterday (although the weather hasn’t changed drastically).

Yesterday after breakfast we went for a 1:30 hour walk. Usually I’d need to cut my insulin in half for a walk like that, but instead, I needed 1.5 times the usual dose (I brought along some of the fruit I’d counted in my breakfast dose but just didn’t eat them). We had a picnic lunch, which I dosed for, plus half a pain au chocolate, then half an ice cream cone, then a few more snacks at home… all in all, it came to twice the carbs I’d bolused for. Dinner was the same - I needed several snacks to keep my blood sugar up.

This morning, we went for a 1:15 hour walk, which I’d usually do 75% insulin for. That seemed to work perfectly. Lunch I planned at 100% but have needed a few snacks already and it’s looking like I should have reduced to at least 60%.

It seems to be quite unpredictable for me. I think I’m still in the honeymoon phase (I was diagnosed in August 2021), so maybe my pancreas is still spurting out some insulin, although if that’s it, I wish it would at least be a bit more consistent!

I’m still managing to keep my TIR at 95%+ by having progressive meals (bolusing for x carbs, but eating them only as I see my blood sugar is coming down or staying steady), so I’m quite pleased about that. It does take a lot of time and attention, though.


That’s a good technique, using carbs to push the BG up as needed. The other side of course is using insulin to push the BG down as needed. The combination of the two is sometimes called “sugar surfing” and I’m a fan.

That’s the attraction of a closed-loop pump system. Every 5 minutes it is trying to push the BG in a good direction by adding or withholding insulin (including basal.) It can’t do the whole job, but it can replace a significant portion of that “time and attention.”


Sugar Surfing does sounds interesting, although I’m not sure how practical it is on MDI. My correction factor is about 100, so one unit would bring me down about 100mg/dL. I think that would make it hard to properly ‘surf’ without a pump.


Back when I was on MDI it was my practice to eyeball the corrections to the nearest 1/4 unit, but anyway I was not dealing with the significant insulin sensitivity that you have. It sounds challenging for MDI so long as that degree of sensitivity continues. And yes, a pump would make it much easier to microdose.


I’ve made a spreadsheet that calculates the fraction of unit I need for a correction, along with the carbs I plan on eating so I can add or subtract carbs (or adjust my target blood sugar a reasonable amount) to get to, or within .1 units of, the nearest full unit.

Tomorrow I get to crack open a Humalog Junior pen, so I’ll get to play with half units. :smiling_face: With my insulin sensitivity, it should mean fewer carb adjustments.


I’ve pretty strongly believed summer heat reduces insulin effectiveness for quite a few years. This year has been different enough to change that conviction.

I engage in some sort of endurance sport (running, biking, skiing) year round. Typically training is predominately sub threshold (“aerobic”) during the winter and spring and transitions to more high intensity efforts as races start in the spring/summer. At that point there will be 2-3 “intense” sessions a week, interspersed with easier workouts and occasional easy weeks. My daily insulin needs usually go up 10-25% in the summer months. Because overall training volume is usually the same or higher, and bike KJs are about the same I chalked this up to the heat.

This summer, due to a few weeks off for COVID, I ended up doing more of my winter-style training in the summer heat. To my surprise during that time my insulin needs were atypically low. Then when trying to scramble to get a little racing in, I switched to higher intensity intervals during a wave of cooler weather and I started needing more insulin and my sites lost sensitivity.

I still think there is some effect of heat on the amount of insulin needed, but I’m starting to believe it confounds with my other summer habits of more polarized activity.


I’m in Australia and have the extreme heat that those of you in the Northern hemisphere have been experiencing, every summer for all of my life, depending on my location.

I am extremely sensitive to temperature, especially as I get older!
I’m MDI, and I require more insulin in summer and much less in winter.

As @Eric states above, I’ve always attributed my summer requirements to the fact that your blood circulates faster in warmer temperatures.
As for my winter requirements, my body uses more energy to keep warm and that’s why I don’t need as much in winter.

Of course it’s still a major guessing game, and during winter I have to keep my bedroom heater on all night otherwise I hypo (Australian houses don’t always have the best insulation). But I know how to adjust my insulin in each consecutive season to figure out what my dosages should be for the particular time of year.

Bear in mind that the dosage I’m referring to is my basal. I keep my i:c the same (except for my different times of day changes).

I use Levemir as my basal and I can vary my morning dose by 4u, 26-30 units, and my nighttime dose by 2u, 16-18 units.
So while it’s not a great change, the effect on my levels can be astronomical.
When the season changes to the cooler months, I will often have 2-3 hypos overnight before I reduce that night dose, and then turn the heater on, even if I don’t feel cold.
It annoys me to no end, but until I can afford to pull my bedroom wall apart to add insulation, this is what I need to do. :woman_shrugging:t3: