The HPA axis is a network, connecting the body’s central nervous and endocrine (hormonal) systems and is activated by stressful events to help provide the body with energy for fight or flight.
The HPA axis plays an important role in our response to stress and has three key parts - the hypothalamus, the pituitary, and the adrenal cortex. The hypothalamus is part of your brain and is involved in a variety of processes, including temperature control and breathing. The pituitary is located near the hypothalamus and helps regulate many of the other endocrine glands. The adrenal cortex is found just above the kidneys on the adrenal glands and is involved in metabolic processes.
Stress and cortisol
When a person faces a stressor, physical or emotional, the initial response from our sympathetic nervous system is the secretion of epinephrine (adrenalin) and norepinephrine, producing effects like increased heart rate and perspiration. Shortly after, the HPA axis is stimulated and your hypothalamus responds to signals like elevated norepinephrine levels by secreting corticotropin-releasing hormone (CRH) into the bloodstream, which then tells the pituitary gland to secrete adrenocorticotropic hormone (ACTH) into the bloodstream. ACTH travels to the adrenal cortex, binds to receptors and triggers the adrenal glands to secrete cortisol. Once the adrenals have produced enough cortisol, the hypothalamus stops releasing CRH.
While proper functioning of the HPA axis is essential for dealing with stress, when the HPA axis is stimulated too much, this can lead to health problems. Cells all over your body are equipped with cortisol receptors, and cortisol can trigger many responses, including increased heart rate, increased blood sugar, rapid breathing and heightened senses. Elevated cortisol levels may contribute to low immunity and increased susceptibility to diseases like type 2 diabetes, obesity, and cardiovascular disease. High cortisol may also have negative effects on memory, cognition and mood, and may also contribute to increased anxiety, excess fat deposits and insulin resistance.
Sleep
You need to rest and maintaining long-term good health depends on your ability to get good quality sleep. Cortisol has a powerful influence on the sleep-wake cycle (circadian rhythm). When something disrupts HPA axis function, it can disrupt your sleep cycles as well. Every 24 hours, roughly in tune with day and night, your body enters a period of sleep followed by waking and cortisol levels in your body follow a similar pattern. Cortisol production drops to its lowest point around 12am and peaks around 9am.
What can I do to maintain healthy cortisol levels?
Having regular sleep and wake times helps and getting regular exercise. Practicing mindfulness, meditation, yoga and spending time in nature, may also assist with improving sleep quality and reducing stress. This is in addition to supporting your overall health by eating whole foods, including leafy green vegetables and low GI fruits.
Information sources
Hirotsu, C., Tufik, S., & Andersen, M. L. (2015). Interactions between sleep, stress, and metabolism: From physiological to pathological conditions. Sleep Science, 8(3), 143–152. https://doi.org/10.1016/j.slsci.2015.09.002
Sarris, J., & Wardle, J. (2019). Clinical naturopathy: An evidence-based guide to practice (3rd ed.). Elsevier.
Marieb, E., & Hoehn, K. (2019). Human anatomy & physiology (11th ed.). Pearson Education Limited.