- Excerpt
Now that the days grow shorter in the Northern hemisphere, some of us already begin to feel the coming of what is usually called "winter blues", periods of mood changes, feeling depressed or "empty" and lacking energy. Officially the condition is defined as "seasonal affective disorder" or SAD. What causes SAD? Well, apart from the fact that a sunny day makes most of us happier than a dark one, shorter or no periods of exposure to sunlight means that the skin is deprived of the energy it needs to produce vitamin D. Studies have shown a relationship between vitamin D and people's mood. Supplementing the daily diet with vitamin D particularly when combined with light therapy can improve depression symptoms. [i] What is often overlooked in this matter is that "winter blues" are not just seasonal. They are also "occupational", for instance when they affect people such as night shift workers and operating room nurses who spend most of the day in artificial light. A study performed a few years ago in China sheds light on the association between sunlight exposure and mental health.
Operating room nurses
To find out whether sunlight has an effect on mental health, a group of researchers working at the Shandong University in Jinan (China) compared the mental health status of the general (Chinese) population to that of a group of operating room nurses (ORNs) who have limited sunlight exposure because ... as you may have guessed ... there are no windows in operating rooms. ORNs' often long working hours are predominantly during the day, thus their sunlight exposure out of work is also short. What makes ORNs also perfectly suited for this study set-up is that they have normal social interaction and work characteristics, which makes them epresentative and comparable to the general population.
Sunlight and mental health
The researchers, who work at the University's Centre for Health Management and Policy Research, found that ORNs had a relatively high level of psychological distress. They also found that sleep regularity, chronic diseases and sunlight exposure time are all factors that are associated with mental health. Suffering from chronic diseases is associated with a higher risk of developing mental disorders. People with chronic diseases are more likely to be depressed and anxious than other people. Physical pain increases patients’ psychological stress; therefore, depressive symptoms increase with the diagnosis of chronic illness. Of the 787 study subjects, 314 (39.9%) exhibited a score indicating a poor psychological condition and a high risk of developing psychological disorders. The mean score was significantly higher than that of the general population. In their study, however, the group focused specifically on the influence of sunlight on mental health. ([ii])
Vitamin D does the trick
On the basis of interviews conducted with the ORNs, the researchers calculated that sunlight exposure time exhibited a positive correlation with mental health. As the duration of sunlight exposure increased, survey respondents’ mental health status improved significantly. They indicated that, from a physiological perspective, several explanations exist, the first and foremost of which is the role of vitamin D. Multiple scientific studies, analyses and clinical trials have demonstrated that vitamin D deficiency is associated with an increased risk of depression, and vitamin D supplementation may be beneficial in treating patients with depression. Sunlight exposure has been—and will continue—being the primary source of vitamin D for most people. Thus, sunlight may very well affect mental health by affecting vitamin D levels in the body.
The "vitamin D winter"
When placed in the context of seasonal affective disorder and the relative changes in the length of daylight-periods over the year, it must be noted that Jinan is located at a latitude of 36° N, which is similar to that of Southern Spain and Washington DC. At this latitude seasonal changes in solar UV radiation and length of daytime are relatively moderate but certainly measurable. Although the Shandong study was conducted during the months of December and January, the sun was apparently strong enough to have an effect on vitamin D synthesis. In other words, there is no "vitamin D winter" in Jinan. That "winter", though, does exist for all people who, like ORNs, spend most of the daytime in artificial light conditions, no matter where they are located on the map.
SAD and "OAD"
The researchers were aware of the fact that several factors influence mental health. Whether increased sunlight exposure leads to improved mental health, or good mental health seeks more sunlight, or a combination of the two is difficult to verify. Despite these limitations, this study is consistent with the view held in most previous studies that mental health status improves with increased sunlight exposure time. What does this have to do with you? Well, although people working in operation rooms are exceptionally under-exposed to sunlight, fact is that most people living and working in "Western" type non-daylight situations are also seriously under-exposed. Besides this, although a mental health score comparison between ORNs and the "general population" shows the importance of sunlight exposure, it doesn't show that sunlight exposure of the general population is sufficient. Living at higher latitudes brings seasonal affective disorders just like spending your days in artificial light conditions brings similar Occupational Affective Disorders. Imagine what a combination of both SAD and "OAD" does to your mental and physical health.
Balancing the good and the bad of sunlight
People who try to catch up on solar UVB radiation by taking a "winter holiday to the sun" or spending hours in a solarium should still be aware of the fact excessive exposure to sunlight won't restore what was lost during periods of under-exposure. Such efforts will do more harm than good. Moderation is the word and UV-blockers (sunscreens) produce the opposite of what sunlight exposure should accomplish: production of vitamin D. The safest way to balance the positive and negative effects of exposure to sunlight is a daily dose of antioxidants to prevent radiation-induced formation of free radicals that damage the skin. In this regard, as demonstrated by Dr. Jack Masquelier in a free-radical scavenging test he performed on his own arm, OPCs may be regarded as uniquely helpful. And, as reported in a previous article, it's always wise to supplement your diet with vitamin D, preferably in dosages exceeding the official daily requirements. That's really a sign of ... mental health!
[I] The Sunlight Solution; William F. Supple, jr., PhD; Skyhorse Publishing, Inc., Delaware; MAH Books, 2026.
[ii] Association Between Sunlight Exposure and Mental Health: Evidence from a Special Population Without Sunlight in Work; Jie Wang, Zhen Wei, Nan Yao, Caifeng Li, Long Sun. Shandong University, Jinan, People’s Republic of China; Risk Management and Healthcare Policy, 14 june 2023.
