Indirect - since it doesn't affect the amount of Path of exile currency health points - a way to improve the nature's endurance is to increase its defensive parameters - i.e. protection, dodging and resistance to specific components. This will not increase the amount of health points, but you'll lose less with every blow that is received.
To restore health, you can:
Use potions - Life Flask and Hybrid Flask items allow you to restore a particular number of health points.
Steal Life - the Life Leech parameter lets you restore health points dependent on the proportion of damage dealt, e.g. 1 percent of damage dealt with enemies, which is restored because of a character's health. Recover points based on strikes and kills - the Life on parameter permits you to restore a particular number of health issues for every enemy hit, while Life on Kill restores health for every killed opponent. Return to the city - a trip to the town will restore health.
Lighting mechanisms, or more exactly the assortment of lighting (Light Radius), can also be connected with health points. The proportion of health points affects the amount of light - the lower it's, the poorer the light will be. This mechanisms can be changed with buy POE orbs the Arcane Vision passive ability .