there absolutely has - you can go down the google search rabbit hole to read them if you have a year or two to spare long story short - short exposure to heat either with ‘boiled’ kettle water or a quick heat up in the microwave isn’t going to do much to them at all.
Thanks for the replies, I have seen some posts about heating usually just talk about preferences and texture etc and one mentioned that boiling water may cause some loss of vitamin c and effect proteins but no indication of how much it may be effected.
I had a go any way using caramel coffee powder I used 500ml of hot but not boiling water added a spoon of coffee and sweetener then two scoops of powder.
I found the texture was thicker and less gritty than cold mixing. I drank half hot as a snack replacement and then refrigerated the remaining half to try it cold in the morning.
Vitamin C is one of the ones that is damaged the most, but again, all of these test results are from exposure to sustained high temperatures - so adding some kettle ‘boiled’ water is not sustained heat as it begins cooling immediately. I had a quick look online and Vitamin C under sustained heat lost on average 13% after 5 minutes, 34% after 15 minutes and 58% after 30 minutes. There are many variables that affect that so you can only approximate.