Is there such a thing called 'sub-optimal health'? is there science to back it up?

The term is used: in the United States, but seemingly not as formally as in China where sub-health is a synonym. It attempts to describe a state of being neither healthy nor ill, but not feeling really well; not a precise condition.Symptoms include fatigue, chronic aches/pains, trouble sleeping nervousness, poor mood. Criteria (such as increased BMI, blood sugar, etc) have been developed/used principally in China.