Suboptimal health status (SHS), or subhealth or sub-health(Chinese:亚健康), can be defined as a state characterized by some disturbances in psychological behaviors or physical characteristics, or in some indices of medical examination, with no typical pathologic features. It is considered as a therapeutic working concept which defines an intermediate stage between health and disease, which is not quite either status. Human persons who are sub-healthy have any of a range of uncomfortable symptoms but without any obvious and diagnosable illnesses which can be identified through standard medical observation methods. This concept was first presented as "the third state" by the scholar of former Soviet Union, Berkman, in the mid-1980s. It is also interpreted as different terms like "intermediate state", "grey state" or "a general malaise". Sub-health is a term which is widely used by Chinese people, or in connection with traditional Chinese medicine (TCM).

Some feel that the notion of SHS has been invented to sell people medical products.

Signs and symptoms

Signs and symptoms considered indicators of SHS include aches, chronic fatigue, indigestion, sleep disorders, congestion, nervousness, distraction, nausea, and poor mood.

Diagnosis

SHS was measured by the suboptimal health questionnaire (SHSQ-25) including 25 items.Each subject was asked to rate a specific statement on a five-point Likert-type scale, based on how often they suffered various specific complaints in the preceding 3 months: (1) never or almost never, (2) occasionally, (3) often, (4) very often, and (5) always. The raw scores of 1 to 5 on the questionnaire were recoded as 0 to 4. SHS scores were calculated for each respondent by summing the ratings for the 25 items. A high score represents a high level of SHS (poor health). The Cronbach’s α coefficient of the SHSQ-25 was 0.91, indicating good internal consistency. The final questionnaire congregated into a score (SHSQ-25) which could significantly distinguish among several abnormal conditions and could be used as a translational medicine instrument for health measuring in the general population.

Another criterion for diagnosis of subhealth was defined as the presence of ≥ 1 of the following abnormalities: body mass index ≥ 25 kg/m2 or waist circumference ≥ 102 cm in men and 88 cm in women; systolic pressure 120-139 mmHg and/or diastolic pressure 80-89 mmHg; serum triglyceride level ≥ 150 mg/dL and/or total cholesterol level ≥ 200 mg/dL and/or high-density lipoprotein cholesterol level < 40 mg/dL in men and 50 mg/dL in women; serum glucose level 110–125 mg/dL; estimated glomerular filtration rate 60-89 ml/min/1.73 m2; levels of liver enzymes in liver function tests between 41-59 U/L, or with fatty liver disease but < 33% of affected hepatocytes; levels of oxidative stress biomarkers beyond the reference range of 95%; or problems with both sleep quality and psychological state.