Behavior and metabolic disease.

The link between behavioral factors and disease is not well-defined. Although connections between a fight-flight reaction to environmental stress and hypertension have been much discussed, a potential disease association to a defeat-type of reaction has been much less considered. This is characterized by an elevated activity of the hypothalamo-pituitary-adrenal (HPA) axis, which is difficult to measure over a sufficiently long period of time. There is now considerable evidence that the characteristic peripheral endocrine abnormalities following a chronic HPA axis activation is directing storage fat to central, visceral adipose tissue depots. This evidence come from detailed molecular and cellular studies, clinical observation, and intervention trials, as well as from statistical associations between visceral fat accumulation and HPA axis activation in a number of conditions. Central fat accumulation measured conveniently as the waist/hip circumference ratio (WHR), is therefore probably a surrogate measurement for a chronic or repeated activation of the HPA axis. The WHR consequently provides a possibility to examine connections between environmental factors resulting in a hyperactive HPA axis, which is a consequence of a defeat-type of reaction to perceived stress. Such statistical associations have been examined in several population samples. The WHR has been found to be linked to a number of psychosocial and socioeconomic handicaps among both men and women, as well as to traits of psychiatric disease and use of alcohol and tobacco. Measurements of moderate obesity without WHR elevation often show reverse relations. It is suggested that measurements of central fat distribution such as the WHR may be used as a surrogate for chronic or repeated HPA axis activation, a consequence of a defeat-type of reaction to perceived environmental stress. This may provide a novel, convenient method to trace adverse bodily consequences of environmental stress leading to disease. This is also suggested by the fact that the WHR is now an established, unusually powerful risk factor for several prevalent diseases, which were previously suggested to have links to psychosocial and socioeconomic handicaps.