there's a bit of a misconception about people in the Middle Ages... they were in fact quite healthy..
it's only with urbanisation, that people started to develop illnessess and plagues and other such niceties..which drastically cut down the figures of population..and of general health.. in fact life expectancy was somewhat higher in the middle ages than it was in the decades/century following them.
Although, as with everything, that depends, on where and when. Parts of (greater) Europe prospered while others wallowed. There were periods of great prosperity, and periods of great hardship (often when increased density of population led to rapid spreading of a disease, or to war, which led to famine, etc.)
The Middle Ages are basically a fudge that sit comfortably in neither the "modern" box nor the "ancient" one, and generalising about them is extremely difficult.