Stress and reproduction: central mechanisms and sex differences in non-rodent species

Despite extensive research, the mechanisms by which stress affects reproduction are unknown. Activation of stress systems could potentially influence reproduction at any level of the hypothalamo-pituitary gonadal axis. Nonetheless, the predominant impact is on the secretion of gonadotrophin releasing hormone (GnRH) from the brain and the secretion of the gonadotrophins, luteinizing hormone (LH) and follicle stimulating hormone (FSH), from the gonadotrophs of the anterior pituitary gland. When stress is prolonged, it is likely that secretion of the gonadotrophins will be suppressed but the effects of acute stress or repeated acute stress are not clear. Different stressors activate different pathways for varying durations, and the actions of stress vary with sex and are influenced by the predominance of particular sex steroids in the circulation. The mechanisms by which stress influences reproduction are likely to involve complex interactions between a number of central and peripheral pathways and may be different in males and females. To understand these mechanisms, it is important to determine the stress pathways that are activated by particular stressors and to establish how these pathways affect the secretion and actions of GnRH. Furthermore, there is a need to know how stress influences the feedback actions of gonadal steroids and inhibin.

The non-advertising effects of screen-based sedentary activities on acute eating behaviours in children, adolescents, and young adults. A systematic review.

Sedentary screen time may be an important determinant of childhood obesity. A number of potential mechanisms to explain the link between screen time and increased bodyweight have been proposed; however, the relationship appears to be best explained by the effects on dietary intake, which is attributed to either food advertising or effects independent of food advertising. Technological advances have allowed for greater accessibility and exposure to advertisement-free screen-based media. This review was conducted to systematically synthesise the evidence from laboratory based studies which have investigated the non-advertising effects of screen time (TV viewing, sedentary video games, and computer use) on dietary intake in children, adolescents, and young adults. MEDLINE, PubMed, PsychInfo, CINAHL, and Embase were searched from inception through 5 July 2013. Ten trials met the inclusion criteria and were included in the review. Risk of study bias was judged to range from low to high. Screen time in the absence of food advertising was consistently found to be associated with increased dietary intake compared with non-screen behaviours. Suggested explanations for this relationship included: distraction, interruption of physiologic food regulation, screen time as a conditioned cue to eat, disruption of memory formation, and the effects of the stress-induced reward system. Due to the limited number of high-quality studies available for this review, our findings are preliminary. More work is required to better establish the link between dietary intake and advertisement-free screen time and assess whether differences exist between the different screen-based activities.

Hair cortisol levels, perceived stress and body mass index in women and children living in socioeconomically disadvantaged neighborhoods: the READI study

Disadvantaged communities provide adverse psychosocial exposures that have been linked to high levels of stress, and this may provide one explanatory pathway linking socioeconomic disadvantage to obesity. This study used hair cortisol analysis to quantify associations between stress and body mass index (BMI), and between hair cortisol and perceived psychological stress levels, in women and children living in socioeconomically disadvantaged neighborhoods. Participants were a volunteer sample of 70 women from the Resilience for Eating and Activity Despite Inequality study, including 30 maternal-child pairs. Women self-reported body weight, height and perceived psychological stress using the Perceived Stress Scale (PSS), and provided hair samples for themselves and their child. Children's body weight and height were measured. Following extraction, hair cortisol levels were measured using enzyme-linked immunosorbent assay. Multiple linear regression models examined associations between stress and BMI, and between hair cortisol and perceived stress levels in women and children. Women's hair cortisol levels were not associated with their BMI or PSS scores. Women's PSS scores were positively associated with their BMI (p = 0.015). Within maternal-child pairs, mothers and children's hair cortisol levels were strongly positively associated (p = 0.006). Maternal hair cortisol levels and PSS scores were unrelated to their child's zBMI. Children's hair cortisol levels were not associated with their zBMI or with their mother's PSS score. Findings suggest that cortisol-based and perceived psychological measures of stress may be distinct among women and children living in disadvantaged neighborhoods. Perceived psychological measures may be more important predictors of weight-related risk.