It took me a long time to figure this out. Some of my health issues have been caused from chronic heat stress, related to wearing thick padding and not changing it often enough. I would often get muscle spasms, very stiff muscles, and even palpitations. It seemed to happen more often when I was padded, and especially wet.
I always had a habit of making it pretty thick (disposable), with one or sometimes two stuffers.
My A/C unit broke awhile back and I had to live, for close to a week, in 95 degree heat (inside the house). I found that the best way to cool off was to put ice cubes down my diaper. Putting a few ice cubes down there and within seconds I wouldn't even know the A/C wasn't working. A friend told me that there are some arteries that run through that area, so any temperature that is in that area will get quickly transferred to the rest of the body.
So one night (after the A/C was working again of course...) I was having another episode of back pain and general discomfort like I usually get. I was wet and didn't change. I thought I'd try the ice cubes to see if getting rid of the heat down there would solve things. I felt so much better, it was night and day. Now I didn't start feeling bad until the diaper was actually wet. I think that a dry one is OK even with a stuffer. The wetness will actually cause the heat to conduct between the diaper and the skin.
I did some reading on chronic heat stress, and found some studies (in animals) suggesting that elevated temperatures will cause things like high cholesterol, and vitamin A and E depletion, and even fluctuations in the thyroid hormone, which affects so many things. There was one study that showed that taking both vitamin A and vitamin E together mitigated some of the damaging effects of the heat. These are animal studies mind you, so don't read into it too much.
When I talk about heat inside the diaper, in my case it gets HOT in there, and I am a pretty small guy at 135 lbs.
Again, don't read too much into this, but be wary that the heat and conduction from a wet diaper that is thick, and not changed for many hours, is pretty unique to AB/DL and not something that you really see much of with babies or incontinent people since they change quite often and do not keep things thick. So we don't really know for sure if that much heat is doing damage to you as it circulates through your body.
Another factor to consider: since the heat is actually being transferred directly through the arteries, it's not going to be sensed from the body in the same way that you would feel a hot room. You might not actually *feel* hot, and some of your body's anti-heat mechanisms might not be completely functioning because the outside air is already a low enough temperature, the body will sense that, and not cool itself down as much.
So just be careful, please! If you're feeling muscle cramps, try taking a short break from the padding, or put some ice cubes inside the diaper. Changing more often wouldn't hurt too!
Obligatory, possibly meaningless studies: