When Sunlight enters your eyes, it stimulates parts of the retina which then cues the brain to produce Serotonin. The more the brightness, the more it gets produced. 

Impact of sunlight in part of Serotonin release.

Very Often we had mood changes during particular weather patterns like Depression/Sadness during Rainy days and Happiness during sunny days. It does fall under Seasonal Affective Disorder (SAD) if diagnosed. Serotonin has been the mediator in treatment since a long time. A relationship does exist with normal seasonal variation and Serotonin.

Michigan State University

Health Psychology research studies relating to Depression include
- Effects of Major Depressive Disorder (MDD) on People with Chronic Illness
- Seasonal Patterns in Mindfulness and Attitudes in People with Seasonal Affective Disorder (SAD)
- CBT + Exercise vs Treatment as Usual in Treating Anxiety 
and Depression in University Students: A Pilot Study

Health Psychology Research Relating to Depression

Chronic physical and mental illnesses severely impair the daily activities of people. When major depressive disorder presents itself as a co-morbid illness to existing chronic illnesses, patients are more likely to encounter health problems. Generally, people with both MDD and chronic illness(s) had a greater number of healthcare utilizations, work absences, and short-term disabilities than people with MDD but no physical conditions or people with physical conditions but no MDD. 

Effect of Major Depressive Disorder on People with Chronic Illnesses

Seasonal depression, also known as Seasonal Affective Disorder, is a common and reoccurring condition impacting mood and energy level during seasonal changes. According to research, these behavioral changes in response to the environment are correlated with differing seasonal mindsets.

Seasonal Patterns in Mindfulness  and Attitudes in People with Seasonal Affective Disorder (SAD)

Sunlight and Serotonin Takeover in the Brain  

An intervention combining cognitive behavior therapy and exercise may be effective in treating stress, anxiety and mood symptoms among university students, a population with unique barriers to treatment-as-usual CBT.

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