Circadian rhythms and depression

Circadian rhythms

Circadian rhythms are daily cycles based on a 24-hour period which are strongly influenced by regular changes in the environment such as night and day. This natural cycle helps to coordinate regular bodily functions like appetite, energy, mood, and sleep, partly by regulating the timing, amount and quality of the hormones and neurotransmitters the body produces and releases.

When our body is out of sync with this 24-hour cycle, we may be at risk for suffering from a Circadian Rhythm Disorder. In the short term we may experience circadian disruption, such as during jet lag following overseas flights or in shiftworkers. It's not uncommon for people to suffer from mood, anxiety or sleep related disorders at least once during a given year, although this won't necessarily be due to Circadian disruption. 

The master clock

Functioning as a timekeeping mechanism for the mind and the body, the suprachaismatic nuclei (SCN) synchronize the 24-hour periods and control most other rhythms of the body by working with time keeping genes and hormones, such as melatonin. Together they coordinate the daily rhythms and cycles that control the rise and fall of hormones, chemicals and neurotransmitters that determine wake, sleep, appetite, sex and other key aspects of our lives.

Nature's rhythms

Many of the rhythms of our body and mind are synchronised with nature. For example, when our biological clock is functioning properly, the wake drive will start to increase in the morning, as the sun is rising. The circadian system and the sleep-wake system then prompts our bodies to produce cortisol, serotonin, and other hormones that wake us up, increase blood pressure and cause body temperature to rise. Likewise, at sunset, the body receives another cue and responds to the lack of sunlight by producing and releasing the hormone melatonin. Unlike at sunrise, this leads to a decrease in blood pressure and allows the body to prepare for and eventually fall into sleep.

Sleep and disrupting our circadian rhythms

Sleep is an important part of our daily lives. It helps restore our energy, keep our memory functioning properly, and helps to heal our bodies. When sleep is disrupted or deprived, we don't feel as alert as we could, we are easily agitated and all of our actions seem slow and drawn out. It is common that stress and anxiety from demands of work, family, and every day life lead to sleeping problems.

As time has passed, people's lives have become much faster paced. From hectic work schedules, traveling and much more involvement in social activities, we leave little time for ourselves to unwind and relax. Because our lives have been significantly sped up, we tend to get less sleep causing many of us to feel run down and exhausted.

When our bodies are out of sync with the 24-hour Circadian rhythm cycle, rhythm is not regular, and hormone and neurotransmitter release is negatively affected, causing our bodies to potentially suffer from a circadian rhythm disorder (CRD), potentially causing depression.

The best way to minimise the risk of inducing sleep-wake difficulties due to circadian disruption issues is to recognise and correct bad habits leading to the issue. This can mean taking less naps during the day, allowing yourself time to wind down at the end of the day, getting exposure to light in the mornings, exercise, diet and pulling yourself back into a regular pattern by trying to go to sleep and wake up at the same time each night and day.

Circadian rhythm disorders

A circadian rhythm disorder means your body is producing hormones, chemicals and neurotransmitters in the wrong amounts and/or at the wrong time of the day. The timing of psychological, behavioral, physiological, and hormonal rhythms with respect to the day-night cycle, clearly displays how regular patterns and chronological order are essential for optimal health.

Consequently, when our bodies are not in tune with nature's biological cues, this has the potential to lead to negative affects on our mental and physical wellbeing. Because circadian rhythms control the release and timing of hormones, circadian rhythm disorder underlies many mood disorders and sleep disruption.

"Hormone of darkness"

Melatonin is an important night-time hormone associated with sleep and regeneration. However, excessive levels can cause depressive disorders. This hormone is normally released at night as the sunlight disappears, causing people to become tired. If we are awake with melatonin in our system we often exhibit some of the following symptoms: lethargy, disorientation, irritability and moodiness. This explains why depression is highest in the darkest climates. Almost everyone with a mood disorder suffers the most in the winter because of the excessive melatonin in our system. Some of the Seasonal Affective Diosorder effects may also be due to a lack of light exposure, which can affect melatonin secretion, circadian timing (inducing phase shifts) and also has direct alerting effects.

Depression and seasonal affective disorder  

People suffering from depression may have a malfunction in their biological clock, resulting in skewed hormone release. Our body needs serotonin to be active and energetic during the day and melatonin to help pull us back to sleep. But, if the brain is triggered to secrete melatonin during the day, it can cause us to feel dull, unstable, irritable and moody. Oftentimes depression is the result of our bodies producing the wrong hormones at the wrong time of day. This imbalance in the circadian system can be caused from lack of sleep, stress, trauma, inappropriate timing of sleep-wake periods, genetic factors, shiftwork, or lack of light.

Seasonal Affective Disorder (SAD) is the most closely related disorder to CRD. During the months of the year when the days become shorter, the brain's master clock receives insufficient amounts of light, causing it miss certain cues to release necessary chemicals. This can cause malfunctions and result in the production of the wrong hormones at the wrong time of day.

Research also shows that without sunlight, the brain doesn't produce enough serotonin, resulting in the symptoms of depression. The darker days also signal the brain to overproduce melatonin. The symptoms diminish as the days get longer, although many SAD sufferers note brief (1-2 week) periods of SAD like symptoms in the summer.

Bipolar disorder

Bipolar Disorder is different than major depression in that it is marked by episodes of euphoria or mania. These episodes can last for hours, days or even months. In almost all cases of bipolar disorder, depressive and manic episodes are seasonal leading doctors to make a connection between the disorder and CRD. In Autumn and Winter as daylight decreases, bipolar sufferers enter a depressive phase, and require increased intervention. Bipolar sufferers also suffer from sleep problems and feel worse at a particular time of day. Because these symptoms reflect a circadian rhythm disorder, doctors have found success by treating bipolar disorders with bright light.

Light therapy

Researchers have discovered how exposure to bright light stimulates the production of brain chemicals to relieve symptoms related to depressive disorders. Light exposure suppresses melatonin and helps to reset the internal biological clock.

The circadian system gains information about the time of day from the environment via various time cues, with the strongest being changes in light-dark exposure. The circadian system is sensitive to 'normal' light exposure, with specialized receptors in the eye, not used for vision, being stimulated by light entering the eye and information transported to the hypothalamus. It has recently been discovered that these circadian specialized receptors in the eye are more sensitive to particular wavelengths of light or blue light.

When a patient is exposed to light, it enters the eye and via the optic nerve and activates the hypothalamus. Once triggered, the hypothalamus sends a signal to the pineal gland which immediately suppresses the production of melatonin and stimulates the production of serotonin. When serotonin is released negative symptoms are alleviated, making you feel alert and active. Light therapy can be used as a treatment for sleep disorders as well as to reduce the duration of jetlag, by increasing the rate of circadian adaptation a well as via a direct alerting effect.

By using blue light for light therapy, the time of exposure to the light may be shortened, and the brightness of the light may be reduced compared to when 'normal' lgith with all different wavelengths included is used.

Acknowledgement:
The Brain and Mind Research Institute (BMRI)