One of the reasons that the population of Europe was hit so hard by the Black Plague was that is was not healthy, there was a shortage of most of the above. Then after the plague hit the Little Ice age set in which reduced the area under cultivation, took centuries to recover.
The western Roman Empire had a problem with a shrinking population and a reduction of cultivated land starting in about 200, plague (?) they can't find enough bodies to match the stories. Samething with the plague in Justinians' time (532), no bones. As Blam speculated there is evidence of and impact of some sort around that time.