My N=1 could says otherwise, either exercise or sleep or both…
Since following a structure plan for last 18 months I’ve never been healthier… Only changes in my life were ensuring I get the 8 hours sleep and doing regular workouts. Diet and everything else has stayed constant. I got a cold the other week for the first time since I can remember, something like that would have lingered for weeks, moved on to my chest, throat etc… this time the runny nose & the slight headache was gone in under 48 hours, though workouts suffered that week until I realised it was probably that virus affecting me hitting the numbers…
This What Sleep Are You Getting?😴 - #31 by andrewwylie ted talk posted several times in the forum was an eye opener, especially the part of mother nature has never had to deal with people depriving themselves of sleep and how effects immunity system in different ways. Getting your 8 hours is the best defence I believe you can give your body.