Grey Weather, Grey Mood: Cortisol Levels May Underlie Seasonal Affective Disorder

Reading time: 5 – 8 minutes

The relationship between season and psychological health in terms of mood has been greatly researched. A recent study shows the cortisol function differs over season in people reporting “Seasonal Affective Disorder” or SAD [1]. This may finally help us to understand any biological mechanism underlying of SAD.

Seasonal affective disorder

SAD is a recurrent mood disorder, where depression and fatigue are experienced in around the time of winter [2]. It has been treated with bright light [2], with the logic that the difference in light is causing the symptoms; by manipulating the air ions to increase feelings of relaxation [2]; by antidepressants [3]; and by nutritional interventions to address changes in thyroid function [3]. These myriad of treatments assume different underlying causes of SAD, however the evidence of what makes people to experience SAD remains inconclusive [1].

One idea to explain the experience of SAD involves cortisol. Cortisol levels fluctuate with light and dark or wake and sleep cycles. We experience a burst in cortisol levels around 30-45 minutes after we wake up. This is known as the “cortisol awakening response “and plays a role is getting us up and moving. Cortisol is of great interest to psychologists, as it has been shown time and time again to be related to depression, trauma, stress and cancer. Cortisol is released in response to physical and psychological stress, and may reduce immune cell function. As immune cell function can have an influence on tumor growth, cortisol is the biochemical link between positive psychology and cancer survival. Moreover, cortisol is a predictive biomarker for heart attack. So, does cortisol have a relationship to SAD, given that it is linked to depression and is produced with some response to light/dark in the environment, which changes over the seasons?

In a recent study, Thorn and colleagues recruited two groups of people; those experiencing SAD (SAD group) and those who did not (control group), recruiting control participants who matched the characteristics of the participants reporting SAD [1]. Attempting to ensure that the average age of the participants in each group was similar, for example, strengthens the research as differences between results are unlikely to be because of age or other variables. Participants were asked to provide saliva samples to measure cortisol levels and record what time they woke up, how long they slept for, how well they slept and measures of stress, alertness and depression. Participants completed these tasks during November/December and again during June/July. Each time, they completed the measures on two consecutive days; 26 people experiencing SAD and 26 control participants completed all data.

The results showed that there were no differences in characteristics such as age, gender, non-smoker or smoker between the two groups. Data from the summer months showed no differences in cortisol levels between the groups. This is as expected, as SAD affects people in the winter months. Data from the winter months revealed that cortisol levels around the time of waking up in the SAD group were lower than in the control group. At this time, the SAD group reported significantly more depression, stress and anxiety and significantly lower alertness. The cortisol levels during the rest of the day were no different for the two groups. The difference was that the burst of cortisol that is the awakening response was not seen in the SAD group.

The research suggests that cortisol may be linked to SAD. However, as always, caution must be applied to these findings. First, a limitation of this study is the reliance of self-reported SAD. It is unclear how severe SAD may have been or if other psychological conditions were present in any of the participants. The study took place in the UK, where the winter certainly signals darkness, however this does not necessarily contrast to the British summer! The point here may be that differences in light levels are just one element that is potentially different between the two sets of data collection, other environmental effects such as colder weather, more rain or the stress of the festive period may be relevant to this research. Causality cannot be claimed. Other factors may cause cortisol responses to change. Other factors may cause mood to change. Indeed, experiencing SAD may somehow cause changes in cortisol and not the other way around. Nonetheless, the difference between control and SAD group suggests there is a role for cortisol in SAD.

This study shows that changes in mood and behavior are associated with a seasonal variation in the cortisol awakening response. Cortisol levels during the day were not related to mood and behavior across the seasons, just that initial burst. This work gives a possible explanation for what may be causing SAD and further research directed at establishing cause is needed.

What are the symptoms of SAD?

Symptoms of SAD usually appear in the fall and winter when there is less exposure to sunlight during the day. Not everyone who has SAD experiences the same symptoms. Symptoms include, but are not limited to:

  • A drop in energy level
  • Fatigue
  • Lack of interest in normal activities
  • Social withdrawal
  • A change in appetite, especially a craving for sweet or starchy foods
  • Weight gain
  • Irritability and anxiety
  • A tendency to oversleep
  • Difficulty concentrating

SAD may also include some of the symptoms that occur in other forms of depression, including feelings of guilt, ongoing feelings of hopelessness and physical problems (such as headaches). For additional information, visit Mental Health America’s factsheet on Seasonal Affective Disorder (SAD).


  1. Thorn et al. Seasonal differences in the diurnal pattern of cortisol secretion in healthy participants and those with self-assessed seasonal affective disorder. Psychoneuroendocrinology. 2010 Dec 8. [Epub ahead of print]
    View abstract
  2. Flory et al. A randomized, placebo-controlled trial of bright light and high-density negative air ions for treatment of Seasonal Affective Disorder. Psychiatry Res. 2010 May 15;177(1-2):101-8. Epub 2010 Apr 9.
    View abstract
  3. Palinkas LA. Nutritional interventions for treatment of seasonal affective disorder. CNS Neurosci Ther. 2010 Spring;16(1):3-5.
    View abstract
About the Author

Faith Martin, Ph.D., is a PhD-trained research psychologist. Faith is currently studying health and lifestyle interventions at the University of Bath in the United Kingdom. Her research interests include quality of life measurement, promotion of self-management, intervention development and cross-cultural psychology.