Definition of Suboptimal Health

This chapter clarifies the definition of suboptimal health status (SHS). SHS is commonly characterised by reversible loss of vitality, decline of physiological function and less capacity for self-adaptation, which is defined as a period preceding the occurrence of diagnosable manifestations of diseases, and different from either the early stage or preclinical period of diseases. Five domains are mainly used to explain the syndromes of SHS: fatigue, cardiovascular system, digestive tract, immune system and mental state. Based on these five aspects, this chapter also demonstrates a variety of physical or psychological disorders that are closely associated with SHS.