A process of change through which individuals improve their health and wellbeing
Working to improve vs improving implies that working at recovery is separate from experiencing recovery. Recovery starts the moment an effort is made, even if the effort is ineffective. The point is that the person recognizes the need for recovery and makes the effort toward it. Each effort is a step along the way. Also "improve their own health" should simply be "improve their health." Is there somebody else's health I would be improving?