Armor avoids/reduces damage taken.
Health makes you stand longer if you have taken damage.

As higher armor also reduces e.g. damage taken from poison, a low health pool with high armor could be more viable.
But since you don't have to decide whether you can have either a lot of armour or a lot of health, both high armour and high health are possible.

Just try it yourself: without having eaten anything (25HP) let a greyydwarf shaman cast the poison thing on you. If do not wear any armor, you will die fast. If you wear some gear, it will take more ticks of the poison DOT to kill your viking.