What social factors had a negative impact upon the health of ordinary people during the period 1250-1500?

The Early Modern Age saw advances in theory, but not in practice. The most advanced Early Modern physicians were usually town-based, and also:
were well educated and trained
did 'scientific' research
were prepared to contradict the accepted authority
disseminated their findings
relied on royal support
had limited success
However, they charged very high fees and only the richest people could afford them.

It was a combination of conquests and alliances