Early-Life Stress, HPA Axis Adaptation, and Mechanisms Contributing to Later Health Outcomes

The brain is the key organ of stress reactivity, coping, and recovery processes. Within the brain, a distributed neural circuitry determines what is threatening and thus stressful to the individual. Instrumental brain systems of this circuitry include the hippocampus, amygdala, and areas of the prefrontal cortex. Together, these systems regulate physiological and behavioral stress processes, which can be adaptive in the short-term and maladaptive in the long-term. Importantly, such stress processes arise from bidirectional patterns of communication between the brain and the autonomic, cardiovascular, and immune systems via neural and endocrine mechanisms underpinning cognition, experience, and behavior. In one respect, these bidirectional stress mechanisms are protective in that they promote short-term adaptation (allostasis). In another respect, however, these stress mechanisms can lead to a long-term dysregulation of allostasis in that they promote maladaptive wear-and-tear on the body and brain under chronically stressful conditions (allostatic load), compromising stress resiliency and health. This review focuses specifically on the links between stress-related processes embedded within the social environment and embodied within the brain, which is viewed as the central mediator and target of allostasis and allostatic load.

Psychological stress and physical activity (PA) are believed to be reciprocally related; however, most research examining the relationship between these constructs is devoted to the study of exercise and/or PA as an instrument to mitigate distress. The aim of this paper was to review the literature investigating the influence of stress on indicators of PA and exercise. A systematic search of Web of Science, PubMed, and SPORTDiscus was employed to find all relevant studies focusing on human participants. Search terms included "stress", "exercise", and "physical activity". A rating scale (0-9) modified for this study was utilized to assess the quality of all studies with multiple time points. The literature search found 168 studies that examined the influence of stress on PA. Studies varied widely in their theoretical orientation and included perceived stress, distress, life events, job strain, role strain, and work-family conflict but not lifetime cumulative adversity. To more clearly address the question, prospective studies (n = 55) were considered for further review, the majority of which indicated that psychological stress predicts less PA (behavioral inhibition) and/or exercise or more sedentary behavior (76.4 %). Both objective (i.e., life events) and subjective (i.e., distress) measures of stress related to reduced PA. Prospective studies investigating the effects of objective markers of stress nearly all agreed (six of seven studies) that stress has a negative effect on PA. This was true for research examining (a) PA at periods of objectively varying levels of stress (i.e., final examinations vs. a control time point) and (b) chronically stressed populations (e.g., caregivers, parents of children with a cancer diagnosis) that were less likely to be active than controls over time. Studies examining older adults (>50 years), cohorts with both men and women, and larger sample sizes (n > 100) were more likely to show an inverse association. 85.7 % of higher-quality prospective research (≥ 7 on a 9-point scale) showed the same trend. Interestingly, some prospective studies (18.2 %) report evidence that PA was positively impacted by stress (behavioral activation). This should not be surprising as some individuals utilize exercise to cope with stress. Several other factors may moderate stress and PA relationships, such as stages of change for exercise. Habitually active individuals exercise more in the face of stress, and those in beginning stages exercise less. Consequently, stress may have a differential impact on exercise adoption, maintenance, and relapse. Preliminary evidence suggests that combining stress management programming with exercise interventions may allay stress-related reductions in PA, though rigorous testing of these techniques has yet to be produced. Overall, the majority of the literature finds that the experience of stress impairs efforts to be physically active. Future work should center on the development of a theory explaining the mechanisms underlying the multifarious influences of stress on PA behaviors.

It was shown that men who were conceived during the Dutch famine of 1944-1945 had higher rates of obesity at age 19 y than those conceived before or after it. Our objective was to study the effects of prenatal exposure to the Dutch famine on obesity in women and men at age 50 y. We measured the body size of 741 people born at term between November 1943 and February 1947 in Amsterdam. We compared people exposed to famine in late, mid, or early gestation (exposed participants) with those born before or conceived after the famine period (nonexposed participants). The body mass index (BMI; in kg/m(2)) of 50-y-old women exposed to famine in early gestation was significantly higher by 7. 4% (95% CI: 0.7%, 14.5%) than that of nonexposed women. BMI did not differ significantly in women exposed in mid gestation (-2.1%; -7.0%, 3.1%) or in late gestation (-1.3%; -6.3%, 3.9%). In 50-y-old men, BMI was not significantly affected by exposure to famine during any stage of gestation: BMI differed by 0.4% (-3.5%, 4.5%) in men exposed to famine in late gestation, by -1.2% (-5.5%, 3.3%) in those exposed in mid gestation, and by 0.5% (-4.6%, 6.0%) in those exposed in early gestation compared with nonexposed men. Maternal malnutrition during early gestation was associated with higher BMI and waist circumference in 50-y-old women but not in men. These findings suggest that pertubations of central endocrine regulatory systems established in early gestation may contribute to the development of abdominal obesity in later life.