It affects each and every one of us in orders of magnitude which we often underestimate.
Late last year, I found myself studying full time and working full time, whilst trying to juggle all the usual demands of life such as visiting family during the busy Christmas season (I did full time online university all through the holidays - yes, I know, insane! Oh and we moved house.) I was cranky with my partner, tired nearly all of the time and I could feel and see my body holding onto more water and fat.
(Note: I was pregnant at the time of writing this but I didn't yet know it! This could have explained some of the changes in body composition and my emotional state...)