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Is Limited Light Exposure Causing Sadness and Depression in the Modern World?

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Gulle Lalah
Gulle Lalahhttps://scientiamag.org
Gull-e-lalah is a former intern at Scientia's Science Writing Internship (cohort 1) and later, working as a team member. She is a scientist, working in the field of Biotechnology and Molecular Pathology, and has a strong passion for science writing, demonstration and teaching.

In today’s world, we are surrounded by the comforts and advancements technology has brought us. However, amidst these luxuries, a fundamental aspect often goes overlooked – our exposure to natural light.

Enclosed buildings and apartments, with limited sunlight penetration, have become a norm of modern architecture. However, this shift in the modern lifestyle has given rise to an alarming situation of increased depression and sadness cases. This article significantly explores the biological correlation between limited light (sunlight) exposure and the resulting mental health problems, as it correlates to depression.

Lack of Sunlight and Seasonal Affective Disorder ‘SAD’
Lack of Sunlight and Seasonal Affective Disorder ‘SAD’. Photo Gulle Lalah

Sunlight Exposure and Mental Health

Several studies have revealed an association between limited sunlight exposure in routine life and its long-term impact on mood, particularly in developing depression.

A survey was conducted to study the effects of sunlight duration on the incidence rate of depression in China. It was found that little exposure to natural light indeed poses a greater risk of developing depression. Therefore, awareness campaigns should propagate the importance of sunlight to the general public (Ji et al., 2023).

The role of sunlight in preventing depression is evident through the example of ‘Seasonal Affective Disorder’ (SAD), characterized by depressive episodes in winter and a happy mood in the spring and summer when more exposure to sunlight is available. This suggests that natural light exposure indeed impacts the circadian rhythms in a way that leads to depression (Komulainen et al., 2023).

Research has revealed the role of ambient temperatures and sunlight exposure on suicide incidence cases (Gao et al., 2019). Similarly, a study recruiting participants from Greece, Victoria, Australia, and Norway showed a positive association between increased duration of sunlight exposure and reduced rate of depression and suicide cases (White et al., 2015).

Participant Based Studies

The effect of sunlight exposure on mental health was studied, with over 780 Operating Room Nurses (ORNs) from hospitals in China. ORNs are exposed to a low dose of daily sunlight as part of their work routine and the environment. It was revealed that this lifestyle had significantly impacted the sleep cycles and mental health among ORNs, suggesting a need for new policies to avoid such work environments where limited light exposure may lead to mental health problems (Wang et al., 2023).

Similarly, a case-control study, including over 1800 Finnish participants, explored the impact of limited sunlight exposure for 1 year. This controlled environment exposure was then followed by an analysis of results, which suggested a strong link between limited sunlight exposure and the development of specific depressive cases (Komulainen et al., 2023).

Scientific Explanation of Sunlight Linking with Mood Swings

Although studies from different populations have established a strong correlation between daily sunlight exposure and the prevention of depression, there is a need to dig deeper into the scientific and biological explanation of this phenomenon.

According to different research studies, there are three main mechanisms which may be involved in ameliorating the risk of depression under healthy sunlight exposure:

Sunlight Impacts Mood through Vitamin D

This might be new to know that vitamin D is not only a bone mineral but also helps to regulate the happy hormones in our body, i.e., serotonin and dopamine. A study by Spedding (2014) found the favourable management of depression through daily vitamin D supplementation, acting as an anti-depressant.

However, dependence on vitamin D supplementation instead of natural sunlight exposure may lead to heart problems and risk to other health conditions (Razzaque, 2018). It has been shown that outdoor activities and sunbathing can help to increase the blood’s  25-hydroxy vitamin D levels and significantly improve mental health (Taniguchi et al., 2022).

Vitamin D Production Under Sunlight. Photo Gulle Lalah
Vitamin D Production Under Sunlight. Photo Gulle Lalah

Sunlight and the Serotonin Synthesis Pathway

Sunlight exposure stimulates the production of serotonin, a neurotransmitter (brain chemical) associated with mood and sleep cycle. Extended periods spent indoors or in areas with limited light can lead to decreased serotonin levels, potentially contributing to feelings of sadness and depression.

Disrupting the serotonin synthesis pathway due to limited sunlight exposure can significantly affect mental health. How sunlight regulates the serotonin pathway is quite an interesting mechanism.

When we are exposed to sunlight, our eyes have specific photoreceptors (light receptors)  that absorb the blue light wavelength. This signals the brain to make serotonin (Azmitia, 2020). Today, bright light is used as a therapy for Seasonal Affective Disorder ‘SAD’. This therapy also works by enhancing the levels of serotonin in the brain (Bilu et al., 2020; Maruani & Geoffroy, 2019).

Happy Hormone ‘Serotonin’ under the influence of Sunlight
Happy Hormone ‘Serotonin’ under the influence of Sunlight. Photo Gulle Lalah.

Melatonin Synthesis Pathways

We are all familiar with the suntan we get from outdoors on a bright sunny day and how we want to avoid it by staying indoors. However, this very suntan may be your saviour from depression. Biologically, the sleep cycle (circadian rhythms) and moods are related to the secretion of a hormone called melatonin by the brain’s pineal gland.

This happens during the night, so melatonin induces sleepiness and helps to regulate the sleep-wake cycle. This melatonin comes from the chemical conversion of melanin (the skin pigment from sun exposure). Insufficient sunlight exposure disrupts melatonin synthesis, leading to irregular sleep patterns and an increased risk of mood disorders, including depression. (Havaki-Kontaxaki, 2010)

Sunlight and Healthy Sleep-Wake Cycle Regulation by ‘Melatonin’. Photo Gulle Lalah
Sunlight and Healthy Sleep-Wake Cycle Regulation by ‘Melatonin’. Photo Gulle Lalah

Concluding Remarks

Understanding the relationship between limited sunlight exposure and mental health may enable individuals to take proactive steps in preventing conditions such as Seasonal Affective Disorder (SAD), mood swings, and depression. The recent COVID-19 pandemic has forced people to adopt an indoor lifestyle, leading to several depressive and anxiety cases.

The post-COVID time should promote a healthy living style with enhanced and healthy daily dosage of sunlight exposure to promote mental well-being. This can be done by incorporating healthy habits into our busy schedules, e.g., taking frequent outdoor breaks, walking, or spending time in well-lit areas and planning family trips and outings in a more natural outdoor resort (Taniguchi et al., 2022). Embracing sunlight and inviting the positive influence of nature into our lives can illuminate a path towards a happier and healthier future.

“Mental health needs more sunlight, candour, and unashamed conversation.”   

 – Glenn Close


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