I explain four critical aspects of 90-minute sunlight to lower the risks of depression from the growing scientific literature based on my experience and observations.
This story does not include health advice. It is for information, inspiration, and awareness purposes.
A recent large-size study in Nature informs that moderate time spent in outdoor light may contribute to a decreased depression risk, even among people with a higher genetic risk of depression.
While the genetic predisposition to depression is well-established and extensively documented in scientific literature, recent research indicates that lifestyle factors also play a significant role in both the onset and management of depression.
For example, a 2023 paper in Nature informs that the genetic dissection of major depressive disorder ranks as one of the success stories of psychiatric genetics. Genome-wide association studies have identified 178 genetic risk loci and proposed more than 200 candidate genes.
On the other hand, a 2023 meta-analysis in Psychiatry and Clinical Neurosciences highlights that accumulating evidence has suggested the critical role of lifestyle factors in depressive disorder. A sedentary lifestyle and increased screen time confer the risk of depression. Insomnia and disturbed sleep-wake rhythm are also involved in the pathogenesis of depression.
Therefore, based on my years of literature reviews, it would be more accurate to view depression as a condition influenced by both genetic predisposition and lifestyle choices rather than solely determined by genetics. As a personal and professional endeavor, I have been researching depression within a lifestyle context for over three decades.
One of the key symptoms of depression is a lack of energy. Last year, I wrote a story titled Seven Reasons You Feel No Energy, which informed my readers who suffer from lethargy and depressive feelings, which happened to me in my younger years. One of the reasons I mentioned was that “You are not getting enough sunlight or bright light during the day.”
However, more interestingly, I recently wrote a critical story titled The Striking Adverse Effects of Night Light Exposure on Mental Health. The story was based on two recent papers published in Nature. I explained the findings from multiple other studies I had reviewed before.
Even more intriguingly, I received numerous email messages from subscribers of my content on Substack/Converkit, especially scientists and mental health clinicians, expressing that this story was an eye-opener for them. The impact of night light, previously obscure to them, was articulated clearly and backed by recent scientific evidence.
Yet, several readers' intriguing questions inspired this follow-up story. They raised concerns about the genetic implications of depression and whether there was any scientific evidence linking sunlight exposure to these genetic factors. After reading an exceptional paper on this topic from Nature recently, I felt compelled to write this additional piece and offer my readers an informed perspective.
An Overview of the 2023 Paper Nature on Association of time spent in outdoor light and genetic risk with the incidence of depression
This exceptional paper titled Association of time spent in outdoor light and genetic risk with the incidence of depression was published in Nature’s Translational Psychiatry in February 2023.
These researchers also acknowledge that depression is the consequence of both the environment and genes working together. Genetic factors increase depression risk, but it is unclear whether this association can be offset by time spent in outdoor light.
Using this critical research problem, these researchers aimed to determine the ideal duration of outdoor light exposure to reduce depression risk and how this interacts with a genetic predisposition.
Their study involved 380,976 depression-free individuals from the UK Biobank. They categorized participants’ genetic risk for depression into tertiles, and they assessed their outdoor light exposure through surveys. They identified depression cases through hospital admissions.
To determine whether participants developed depression, they compared the characteristics of continuous and categorical variables at baseline using a t-test, Mann–Whitney U-test, and chi-squared test, respectively.
For those interested in details, these tests help researchers understand if there are important differences or connections in their data. They increase the quality and credibility of research in quantitative studies. These tests are valuable tools for researchers to make sense of their data and make intelligent choices for their studies.
The t-test looks at whether the average values between the two groups are different. The Mann-Whitney U-test helps when the data doesn’t follow a normal pattern or is hard to rank. It checks if there are differences between the two groups based on their ranks. The chi-squared test is used when data is grouped into categories. It helps see if there are essential differences in how things are grouped.
Their findings revealed a J-shaped relationship between outdoor light exposure and depression risk, with 1.5 hours per day associated with the lowest risk. Both lower and higher exposure times increased depression risk, shortening the time to depression onset.
People with high genetic risk and below/above the optimal exposure had higher depression risk compared to those with low genetic risk and average exposure. They observed multiplicative interactions between intermediate genetic risk and longer outdoor light exposure.
They found that an average of 1.5 hours a day spent in outdoor light was associated with a lower depression risk, whatever the degree of depression genetic predisposition.
So, they concluded that moderate time spent in outdoor light may contribute to a decreased depression risk, even among people with a higher genetic risk of depression.
In this study, they looked at how time spent outdoors in natural light relates to the risk of depression. They used a big group of people to study this. They also checked how genes and outdoor time together affect depression risk. However, their study has some limitations.
Firstly, people reported their outdoor time, which might be inaccurate. Secondly, everyone in the study was white, and outdoor light varies by place and race. So, they were not sure if their findings apply everywhere.
Third, other factors like work stress and where people live also affect depression risk. For example, people in rural areas might spend more time outdoors but have lower incomes. Also, they couldn’t consider everything that might affect depression risk, like job details or weather.
Finally, they only looked at hospital records to see who had depression, which might not catch everyone. The participants in their study might be healthier than others, so they might miss some cases of depression. In the future, more studies with different groups of people and better methods are needed to confirm their results.
However, this study is a new contribution to the literature on depression. Therefore, I want to highlight this knowledge construct here.
You may wonder why sunlight is so critical for depression. I will cover this under four headings to give you valuable perspectives based on my research. Sunlight can affect depression from several angles.
The 4 Magic Formula of Sunlight for Depression
In this section, I will distill my three decades of research on critical factors impacting depression within the context of sunlight without going into too much scientific or technical detail.
1 — Circadian Rhythm Regulation via Sunlight
Firstly, as I documented in my previous story, sunlight exposure helps regulate our internal clock, known as the circadian rhythm, via the Suprachiasmatic Nucleus. This specific brain region helps regulate our sleep-wake cycles.
A stable circadian rhythm is essential for maintaining healthy sleep-wake cycles, hormone regulation, and mood stability. Disruptions to the circadian rhythm, such as irregular sleep patterns or reduced exposure to sunlight, can contribute to depressive symptoms.
Apart from the recent Nature study I covered in my previous story, this 2021 cross-sectional study in PLOS One (peer-reviewed) examined the link between sunlight exposure and depressive symptoms among 1,429 Chinese women aged 60 and older. It found that greater sunlight exposure was associated with a lower prevalence of depressive symptoms.
I referenced the Chinese study because the Nature article focused solely on British participants. Incorporating data from another gene pool provides additional valuable insight into the topic.
2 — Vitamin D Production from Sunlight
As I also covered in another story a few years ago, sunlight exposure stimulates vitamin D production in the skin. Vitamin D plays a role in brain function and mood regulation, and low levels of vitamin D have been linked to an increased risk of depression.
The genetic impact of Vitamin D is well documented in the literature. As I documented in my 2021 story, vitamin D is a potent epigenetic regulator influencing more than 1000 genes.
Therefore, any improvement in vitamin D status will significantly affect the expression of genes with a wide variety of biological functions of more than 160 pathways, as documented in this 2013 double-blinded clinical study.
For example, in a 2013 systematic review and meta-analysis by Cambridge University, after analyzing one case-control study, ten cross-sectional studies, and three cohort studies involving 31,424 participants, it was found that people with depression tend to have lower vitamin D levels compared to those without depression.
In the cross-sectional studies, there was an increased likelihood of depression for people with the lowest levels of vitamin D compared to those with the highest levels. Similarly, the cohort studies revealed a significantly higher risk of depression for individuals with lower vitamin D levels compared to those with higher levels.
3 — Anti-Inflammatory Effects of Sunlight
Despite cancer risks, exposure to ultraviolet radiation from sunlight has been shown to stimulate the production of some anti-inflammatory proteins called cytokines.
As a side note for clarification, cytokines can be either pro-inflammatory or anti-inflammatory, depending on the specific type and context in which they are produced and act. Major anti-inflammatory cytokines include interleukin (IL)-1 receptor antagonist, IL-4, IL-10, IL-11, and IL-13.
Inflammation is closely linked to depression, with elevated levels observed in people experiencing depressive symptoms. Hence, sunlight exposure may indirectly benefit depression by anti-inflammatory boosting cytokine levels, which help counteract inflammation.
For example, this 2010 meta-analysis in Biological Psychiatry reported significantly higher concentrations of the proinflammatory cytokines TNF-alpha and IL-6 in depressed subjects than in control subjects. Proinflammatory means causing inflammation.
While both positive and negative results have been reported in individual studies, this meta-analytic result strengthens evidence that depression is accompanied by activation of the the inflammatory response system.
4 — Serotonin, Melatonin, Cortisol, Dopamine, and Adenosine Regulation via Sunlight
I have left the hormonal impacts of sunlight for last, as they play a crucial role in mood regulation, sleep patterns, appetite, and behavior, all of which have direct or indirect links to depression. Drawing from my extensive research on biochemicals, I will outline the essential points regarding the influence of hormones and neurotransmitters on depression.
Sunlight exposure can trigger the release of serotonin in the brain, a neurotransmitter that regulates mood, sleep, and appetite. Higher serotonin levels are associated with improved mood and reduced symptoms of depression, highlighting the importance of sunlight in maintaining mental well-being.
Exposure to sunlight during the day helps suppress melatonin production, a hormone that promotes sleep. Proper melatonin regulation is crucial for maintaining energy levels and mood throughout the day. Reduced sunlight exposure, especially in winter or regions with limited daylight, can lead to increased melatonin production and symptoms of seasonal affective disorder, a form of depression linked to changes in seasons.
Sunlight exposure might influence cortisol levels, with natural light exposure during the day helping to regulate the body’s stress response. Adequate sunlight exposure can help maintain balanced cortisol levels, which affect mood regulation. Conversely, insufficient sunlight exposure, particularly during the darker months, may contribute to elevated cortisol levels and an increased risk of depression.
While primarily associated with pleasure and reward, sunlight can also influence dopamine levels. Sunlight exposure has been linked to increased dopamine production, which may contribute to feelings of happiness and well-being. Dopamine’s role in mood regulation highlights the importance of sunlight exposure in maintaining mental health.
Sunlight exposure can impact adenosine levels indirectly through its influence on sleep-wake cycles. Adequate exposure to natural light during the day helps regulate the body’s circadian rhythm, affecting adenosine levels and sleep quality.
Disruptions in sunlight exposure, such as those experienced during the winter months or in regions with limited daylight, can disrupt the body’s natural sleep-wake cycles, potentially leading to imbalances in adenosine levels and an increased risk of depression.
Spending time outdoors in natural sunlight can have psychological benefits, such as reducing stress, improving mood, and increasing feelings of relaxation and well-being. Activities like walking, gardening, or simply enjoying nature in sunlight can provide a mood boost and alleviate symptoms of depression.
I explained the roles of melatonin, adenosine, and cortisol in an article on Newsbreal before.
How to Balance Risks and Benefits of Sunlight: Insights from 2024 Australian and New Zealand Journal of Public Health Study
In February 2024, this paper titled Balancing the risks and benefits of sun exposure: A revised position statement for Australian adults was published in the Journal of Australian and New Zealand Journal of Public Health. I highlight the key points to give you an informed perspective.
Researchers pointed out that sunlight has both good and bad effects on health. Too much sun exposure can harm the skin and eyes, causing skin cancer and eye problems. Australia has a high rate of skin cancer due to its strong sunlight. However, sunlight also helps the body make vitamin D, which is essential for strong bones.
Despite Australia's sunny weather, many people don’t get enough vitamin D. Finding the right balance between the risks and benefits of sunlight is tricky because the same sunlight that helps make vitamin D can also cause skin cancer. Some people are more at risk of harm from sunlight than others.
In Australia, there’s been confusion about how much sun is safe, leading to misunderstandings and poor sun protection habits. Many Australians worry about insufficient vitamin D and may not use enough sun protection. Even doctors are worried about vitamin D levels and sun exposure.
A statement was released in 2016 to help people understand how to balance sunlight's risks and benefits. With new research and changes in advice, it’s important to keep reviewing what we know about sun exposure and health.
Their results show that the risks and benefits of sun exposure vary for different people. Those with a high risk of skin cancer should prioritize sun protection to avoid harm.
Conversely, people with darker skin, with a low risk of skin cancer but prone to vitamin D deficiency, may not need as much sun protection. For those with a medium risk of skin cancer, it’s important to balance sun protection with getting enough sunlight for vitamin D.
So, this new position statement provides sun exposure advice that explicitly recognizes the differing needs of Australia’s diverse population, which might also apply to other countries.
Conclusions
The relationship between sunlight exposure and depression is multifaceted, involving genetic predisposition, environment, relationships, psychology, and lifestyle factors.
As highlighted in this story, recent research sheds light on the critical role of sunlight in lowering the risk of depression, even among people with higher genetic susceptibility.
Moderate exposure to natural sunlight is essential for maintaining physical and mental health. It can also reduce the risk of depression and improve mood regulation.
An optimal amount of outdoor light exposure is associated with the lowest risk of depression while deviating from this optimal range can increase the risk and accelerate the onset of depression symptoms.
Besides, sunlight exposure must be balanced with appropriate sun protection measures to prevent skin damage and reduce the risk of skin cancer, a public health concern.
Key Takeaways of this Story
While genetics play a significant role in depression, environmental and lifestyle factors like sunlight exposure also have a substantial impact on depression risk.
Genome-wide association studies have identified many genetic risks for depression, emphasizing the complex relationship between genetics and environmental factors.
A sedentary lifestyle, excessive light at night, increased screen time, and disrupted sleep patterns are associated with higher depression risk, highlighting the importance of lifestyle interventions.
Sunlight exposure regulates circadian rhythms, stimulates vitamin D production, boosts anti-inflammatory proteins, and influences neurotransmitter levels, all contributing to mood regulation and mental well-being.
A new suggests that moderate sunlight exposure, around 1.5 hours per day, is associated with the lowest depression risk, irrespective of genetic predisposition.
Finding the right balance between sun exposure and protection, considering individual skin cancer risk and vitamin D needs, is vital.
While genetic predisposition sets the stage for depression, lifestyle choices, including sunlight exposure, play a significant role in its prevention and management.
Understanding and optimizing sunlight exposure can profoundly affect mental health and well-being, making us more energetic and joyful.
Thank you for reading my perspectives. I wish you a healthy and happy life.
If you found this story helpful, you may also check out my other articles on NewsBreak. As a postdoctoral researcher and executive consultant, I write about important life lessons based on my decades of research and experience in cognitive, metabolic, and mental health.