I just picked up D3 yesterday. It's the kind that looks like vitamin E in the gel caps but they're small... 400iu i think.
The weird thing is, I never ever get colds or flu... the whole house can be sick all winter and I'll be fine.
But if I spend too much time in cold air without a scarf, I'll get bronchitis that lasts all winter. Just clear mucus.. sometimes yellowish or white that turns back to clear. It's like irritation rather than a germ. It's very weird. My grandmother was the same way... never sick, just random bronchitis triggered by cold air.