Can dogs serve as stress mediators to decrease salivary cortisol levels in a population of liberal arts college undergraduate students?

First introduced to physiological and biological literature by Selye74, the term “stress” was first defined as a physiological response that organisms exhibit with respect to both positive and negative challenges. Continued research has broadened Selye's original definition to include that a stress response is mounted in response to stimuli in which predictability and controllability are at risk44;52;70. More recent research has now simplified the concept of stress and states that stress occurs when environmental conditions disrupts homeostasis21. In humans, physiological stress can be mediated by the concentration of the hormone cortisol. Cortisol is a steroid hormone synthesized in the body via the hypothalamic-pituitary-adrenal (HPA) axis71, where a stressor signals the hypothalamus to secrete corticotropin-releasing-hormone (CRH) which stimulates the anterior pituitary gland to release adrenocorticotropic hormone (ACTH). In the adrenal glands on the kidneys, ACTH stimulates the release of glucocorticoids such as cortisol which then travel to target tissues via the circulatory system76;34. Cortisol exerts its effects on target tissues by first activating the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR). These receptors bind cortisol and translocate it to the nucleus where it drives gene transcription and protein synthesis30. Cortisol primarily serves to mobilize and prioritize energy to meet the demands of the stressor76;28. This pathway is generally regulated by a glucocorticoid negative feedback loop, such that more cortisol secretion leads to diminished CRH and ACTH release to prevent an excessive stress response, however, this feedback system can be disrupted by chronic stress53;30. The concentration of cortisol within blood, urine, and saliva is positively associated with stress levels or circadian rhythm, the natural internal process that regulates sleep-wake cycle, functioning in humans77;59.

At low concentrations, the cortisol stress response can improve cognitive and physical functionality to better respond in times of stress71. However, excess cortisol can be potentially harmful in a variety of ways, resulting in long-term effects related to the presence of chronic stress24;71. Accumulated stress can lead to many negative health outcomes highlighted elsewhere11;31;27;85.

In addition to detrimental whole-body health impacts, chronic stress can be related to increases in mental health disorders such as depression and anxiety67;40;39;37. Due to chronic increases in cortisol concentrations and thus greater mental illness susceptibility, scientists have found instances of depression manifesting clinically in symptoms such as increased risk for obesity, cardiovascular disease, and hyperglycemia6;29; Blaine 2008;16;50. Furthermore, high cortisol levels are also associated with increased mortality and risk of hypertension (high blood pressure) and diabetes mellitus72. Evidence suggests that the onset of psychiatric disorders in 75% of patients occurs between the ages of 17-24, which generally aligns with the period of higher education for US students who decide to attend college, and that vulnerability to such conditions is closely related to an inability to successfully manage chronic stress54. With the onset of the COVID-19 pandemic, depression rates have significantly increased in the United States among most demographic populations19. Many would argue that stress has reached epidemic levels, emphasizing the need for greater awareness surrounding effective coping strategies to help people manage their cortisol57, one such coping strategy can be the presence of dogs on college campuses. Negative impacts of chronic stress to physical and mental health are trending upwards, including the prevalence of anxiety and depression in young adults, among stressed populations78; Reetz et al., 2014;13. These mental health problems for undergraduate students are only worsened by sleep deprivation and drug and alcohol abuse present on college campuses59. Additionally, small, private liberal arts colleges have been found to have significantly higher academic challenge and higher expectations than research institutions or regional institutions2;73;48. The ability to mediate stress in a particularly high stress environment is important for both the physical and mental health of an individual3. Despite the help of mental health programs on college campuses, there is an urgent need for strategies that provide fast-acting stress remediation.

According to a study conducted by the American Psychology Association, today's college students are statistically the most stressed living adult generation in the United States (2020). Additionally, college students have been disproportionally affected by the COVID-19 pandemic such that 87% report education to be a significant source of stress and 2/3 feel as though planning for the future is impossible7. Maturing in a tumultuous social climate and managing vigorous academic pressures has led America's generation of college students ages 18-23 (Gen Z) to report the highest rating of stress, 6.1 out of 10, out of all adult American generations in the year 20207. Much of the stress experienced by college undergraduate students does not solely include academic and peer pressures, but also feeling lonely, missing family and friends, experiencing interpersonal relationship conflicts, and worrying about financial problems along with personal health, much of which arises from the transition from high school to college15;68. Without a proper coping mechanism, these stressors could lead to poor sleep quality, insufficient sleep, or unhealthy stress mediation techniques that could produce negative cyclical effects through further lack of sleep or quality of sleep, and adverse health effects later on in life (as stated above)81.

Many authors assert that human-canine interactions can reduce perceived stress and salivary cortisol levels9;41;46;65. Common to all steroid hormones, cortisol secretion and transport occurs a length of time after a stimulus is interpreted24. Saliva collection without the correct amount of time for cortisol to be produced or inhibited may result in concentrations that are not indicative of the true stress response. And, previous work conducted to collect salivary cortisol in the presence of a dog used very short time-frames (up to 20 mins)9;41;46;65. Our study sought to examine the effectiveness of human-canine interactions on mediating cortisol concentrations among college students at Colgate University, a smallprivate, liberal-arts college. We recruited 73 students to our study, and following eligibility determination, we had them interact with a dog for 60 mins and took saliva samples at time points 0, 15, 30, and 60 mins during interaction with a dog.

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