[The concept of allostasis and allostatic load: psychoneuroimmunological findings]

Classical theories have conceptualized stress as a reaction to threat to the homeostasis within the organism requiring an adaptive response. However, postulating mechanisms that could link such responses to long-term detrimental health outcomes remains difficult. The allostatic load concept enables us to think about how mediators can be protective in the short run but may have damaging effects when overused and/or not shut off. It further facilitates the formulation of cause-effects cascades to explain the link of dysregulations in stress mediators such as glucocorticoids and catecholamines and increased susceptibility for certain diseases. In the first section, we briefly summarize the theoretical background. We then employ the concept to integrate findings from basic and clinical research on dysregulations of the stress response systems in multiple sclerosis and breast cancer. Based on this model, it seems likely that such dysregulations are implicated in progression and possibly pathogenesis of these diseases. When using allostatic load as a heuristic model, one needs to consider that stress mediators and outcomes are interconnected in a non-linear network.