I have no idea as I am always cold as well, BUT I am thin, olive-skinned, low blood pressure, and HIGH CHOLESTEROL despite plenty of exercise and adherence to a non-processed/whole foods diet with olive oil, fish, and ground flax seed as my primary sources of fat.

My mother and grandmother were always cold and diagnosed with low thyroid. Supposedly, my thyroid is fine though.

I don't understand your intolerance to heat - you say you are ALWAYS cold, but have to find shade in the 80's. Do you mean that you are NOT cold once it hits 80 degrees? I am able to tolerate heat into the 100's and continue to wear long pants and long sleeves in that weather (I never bare my arms and legs in public - not even on the bike).

Hope you find some answers!