Melatonin, SAD and the Circadian Rhythm

Travis DixonBiological Psychology

Melatonin and SAD

Here’s a video that defines SAD and gives some symptoms of this disorder. If you are to explain how melatonin can cause SAD, you need to know the symptoms. This is also applicable to the GLT that focuses on how our environment can affect our physiology and how that can in turn affect our behaviour. 


Here is a link to Avery et al’s 2001 study regarding Melatonin and SAD patients:


Find out more about your circadian rhythm here.

Here’s another study that shows correlations between giving melatonin to patients with depression and their reduced symptoms. However, it may be difficult to find the connection between this research and how it demonstrates the role of melatonin in regulating circadian rhythm.

Explanation of Implications of Avery’s Study – usually I don’t explain research for you, but this has been done to help you understand the difficult connections between this study and the learning target. 

Melatonin’s function is to regulate our circadian rhythm (our sleep-wake cycle). During winter months, we have to wake-up and it’s still dark we may be waking up with high levels of melatonin, which may lead to symptoms of SAD. SAD is more common in the further northern and southern hemisphere countries because their winter nights are longer. One reason for this may be because our modern lifestyles are not in tune with the natural cycle of sunlight in nature, which upsets our melatonin balance.

Melatonin is secreted when nighttime occurs and it gets our body ready for rest. As the sun rises, our melatonin levels are reduced so by the time we wake up, our body is ready to face the day.

Avery’s study showed that a gradual light coming on at 4:30am until 6am reduced the symptoms of SAD more than placebo and bright light groups.

This may be because the melatonin levels were gradually decreasing as the light grew brighter, and so when the participants awoke their melatonin levels were low (as they should be in the morning when we wake).

The reduced SAD symptoms shows that the melatonin levels may have been reduced by the gradual light that simulated dawn so that when participants awoke their bodies were ready to be active. The results show that one function of melatonin is to regulate our body clock so that when the sun comes up the levels are reduced and we are ready to be awake and active.