Super-Charging your HPA Axis: Natural Therapies Supported by Research Part IV: Sleep

Healthy habits with regards to sleep can go a long way in terms of improving our mental and body health


Sleep is a vital component of our life, required to consolidate memories gained throughout the day1. But, there is much more to it. Believe it or not, while we are asleep our brain is busy, keeping our body and mind in optimal health.

Despite the importance of sleep, a lot of us have poor sleeping habits. It is estimated that as many as 45% of all Australians suffer from sleep disturbances2.  Among sleep disorders, insomnia is the most common one, affecting as many as 33% of all Australians. This condition is often associated with psychological and heart-related problems3, as well as, with a myriad of other problems. A review study, which compiled reports by people suffering from insomnia, identified detrimental effects on:

  • physical functioning
  • role limitation due to physical health problems
  • bodily pain
  • general health perceptions
  • vitality
  • social functioning
  • role limitations due to emotional health problems
  • mental health


There are many other chronic sleep disorders beyond insomnia, and they have been associated with conditions like impaired cognitive functions4-5, the decline of brain function6-7, fatigue8, obesity9-10, depression11, diabetes12-13, stroke14, heart disease15-16 and psychiatric disorders17.

A lesser-known aspect of sleep involves our body’s response to stress. It influences the way our HPA axis functions, hence affecting how we respond to a stressor.


Sleep and the HPA axis


The hypothalamic-pituitary-adrenal (HPA) axis is the body’s top response system against stressful events. It is composed of three organs: the hypothalamus region of the brain, the pituitary glands and the adrenal glands. When a stressor enters the body, the HPA axis becomes active and, through the coordinated interaction of these three components, it releases different hormones that help manage the stressor.

Just as important as the HPA axis itself is the regulation of its function. Overactivation or inhibition of the HPA axis can result in detrimental health effects, affecting, for example, our body’s immune and inflammatory responses18-19.

One essential body function that can affect the function of the HPA axis is sleep. Inadequate sleeping-patterns are tightly linked with HPA function, dependent on the sleep stage. For example, deep sleep is associated with low levels of blood cortisol (the main hormone produced by the HPA axis), whereas light sleep is associated with increased cortisol levels20-21. In addition, there is a reciprocal relationship between sleep and HPA function: an overactive HPA axis can lead to light sleep and regular night-time waking, whereas inadequate sleep can promote activation of the HPA axis22.

In one study, a group of participants were sleep-deprived for one night and asked to complete a social stress test, followed by a blood test22 to measure cortisol levels. Another group completed the same tasks but had a normal sleeping schedule. The study found that, compared to the group that slept well, participants who missed a night’s sleep produced significantly higher levels of cortisol, both before and after completing the stress test.

How much you sleep is not the only factor affecting the HPA axis, but also how well you sleep. Sleep quality has been shown to be just as important as sleep length, when it comes to HPA regulation, especially for men. In one study, participants who reported having “bad quality sleep” had decreased levels of cortisol, compared to participants who reported having “good quality sleep” throughout the night. The study also found that this effect was significant in men, but not in women. This difference, the authors argued, may be due to differences in the way men and women deal with stress. There are two well-studied strategies used to regulate emotions: reappraisal and suppression. The authors suggested that, in response to stress, men tend to suppress emotions before sleep and this may cause uneasy sleep, whereas women deal with their emotions and sleep in peace. This idea is supported by previous research, showing that indeed men tend to use suppression more often than women.

Taken together, evidence strongly supports a crucial role of good sleeping habits to improve HPA function, particularly for the regulation of cortisol in your body. Altered levels of cortisol are associated with multiple health conditions. Excessive cortisol, for instance, is associated with weight gain around the face and abdomen, cognition problems, mood disorders, slow healing, and even depression. On the other hand, low levels of cortisol are associated with muscle weakness, abdominal pain, nausea and vomiting.

In addition to following a healthy diet and an active lifestyle, getting enough and good quality sleep is a proven way to improve the functioning of the HPA axis. This, in turn, will help your body maintain optimal levels of cortisol and other hormones.

If you experience insomnia, trouble to sleep or any sleep disorder, it is important to consult with a professional, like your preferred functional medial practitioner, to identify any underlying problems and design a treatment plan.




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