Mood is essential to a happy life and wellbeing. By Marc Sorenson, EdD
Mood (a good mood) is critical to optimal living, and those who work in natural light experience improvement. In addition, a good mood leads to better performance, behavior and psychological health. Furthermore, very few things improve wellbeing like arising early in the morning and walking outside on a sunny day: Our attitude improves too, and our serotonin and endorphin levels increase. Consequently, there is an almost immediate feeling of exhilaration. So, we become happier and less confrontational, and our minds seem to click on all cylinders. This mood change is all due to the morning sun exposure. Does midday sun exposure also help?
Mood and midday sunlight
Later on, around midday, we produce large quantities of vitamin D, and our nitric oxide levels increase. That is, of course, if we are fortunate enough to safely sunbathe (with a lot of skin exposed). As a result, we experience a delicious feeling of relaxation and a lowering of blood pressure as the cares of the day melt away. Therefore, mood is again enhanced.
Mood and sun robbery
Regrettably, due to various factors, most of us live in a society robbed of the sun. We are confined to artificially lighted buildings and poor little cubicles and our mood is crushed. These little cubicles, of course, seem like prison cells that won’t allow our happiness to manifest itself.
Consequently, concerned scientists are recognizing that modern humans suffer from artificial, insufficient light in their lives. So these scientists are advocating a return to natural light. One of their studies on the subject of light and mood is most noteworthy. They, due to their concern about light availability measured the impact of windows and daylight on mood. They studied the physiological, psychological and behavioral health of working nurses. First of all, they used biological measurements, behavioral mapping and data analysis in a nursing unit of two wards. While both wards exhibited similar conditions, one ward had more windows and more natural lighting than the other.
Impressive mood results:
As a result, in the ward with more windows and natural light, the nurses had better health. They had lower blood pressure and higher body temperature, less sleepiness and a better mood. Communication and laughter also increased. Heart rates were shown to be lower with greater exposure to light, and caffeine intake was reduced as well. In conclusion, mood was improved, as was performance. Rana Zedeh, the lead researcher of that study, made the following statement: “Research has shown a range of different outcomes are impacted by sun, including regulation of the circadian rhythm, shorter length of stay for patients, reduced perception of pain for patients, and reduced anxiety and agitation among elderly patients with dementia. Improved outcomes for patients also help staff manage their patients better.”
Change the environment, change the mood.
Finally, one can only imagine the potential benefits that could be realized if unencumbered sun rays are allowed. Vitamin D production would increase, and it is likely that patients as well as nurses would improve their health.
Hence, Dr. Zadeh also made this declaration: “Intelligently designed clinical workspaces could lead to higher safety and quality levels… By default, when we think of a healthcare workspace, we may think of a large, deep building with no windows for staff, little access to greenery or outdoors, an institutional feel, complex way-finding, and monotonous color and lighting. Knowing how the human brain receives stimuli from the environment and constantly changes neural hormonal responses controlling cognitive performance and alertness, we might be able to improve outcomes by creating more vigilant and restorative elements in environments.” The translation is, “elevate your mood by getting out of the little dark boxes and back into the sun.”
First of all, what does the sun do to relieve “the blues?” The answer lies in a chemical responsible for transmitting impulses between nerve cells. This “neurotransmitter,” serotonin, is a natural “upper,” working in synchronization with the natural “downer,” melatonin. So, when we awake to sunshine, light enters the eye and stimulates serotonin production. Because of this reaction, sunlight can dramatically increase serotonin levels in the brain and immediately improve mood.
Dr. Gavin Lambert and his colleagues in Australia measured serotonin levels in response to varying degrees of bright light.  To do so, they drew blood samples from the internal jugular veins of 101 men and compared the serotonin concentrations of the blood to weather conditions and seasons. The remarkable results: Men who were measured on a bright day produced eight times more serotonin. That is, compared to those who were measured on a dismal day. Of course, the mood was improved due to sunlight.
Get your regular, non-burning sun exposure and enhance your good mood!
 Zadeh RS, Shepley MM, Williams G, Chung SS. The impact of windows and daylight on acute-care nurses’ physiological, psychological, and behavioral health. HERD 2014 Summer;7(4):35-61.
 Katy Mena-Berkley. Mood: the Science of Letting the Sunshine In. MD News
 Katy Mena-Berkley. Mood: the Science of Letting the Sunshine In. MD News
 Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD. Effect of sun and season on serotonin turnover in the brain. Lancet. 2002 Dec 7;360(9348):1840-2.
While many doctors know that ultraviolet radiation (UVR) from sunlight reduces risk of breast cancer, they have missed something. UVR stimulates production of vitamin D in human skin. Therefore, many health professionals assume that vitamin D is responsible for the reduced cancer risk. This may lead them to advocate the use of vitamin D supplementation and totally miss the bigger picture. In addition to vitamin D, UVR from sunlight or sunlamps produces many supplementary healthful photoproducts. Among others, nitric oxide, serotonin, endorphin and BDNF are produced by sunlight, and these photoproducts are vital to health. And, it is likely that these healthful photoproducts lead to an inhibition of breast cancer.
New research shows that sun exposure per se is capable of reducing the risk of breast cancer.
Consequently, it should not surprise us that for breast cancer, sunlight’s effects go beyond vitamin D. Researchers at Children’s Hospital Oakland Research Institute, used a murine model (mice) that easily develops breast cancer, and treated them with UVR. Much as we might expect, they found that UVR treatments produced significant anti-cancer effects. Furthermore, they found that neither dietary vitamin D nor topical vitamin D influenced cancer risk. Because of their findings, they stated the following: “UVR’s inhibitory effects occur irrespective of whether or not the treatment increases circulating D3 in the mice.” Also, they made one more important comment regarding their research on breast cancer and UVR. “Therefore, supplemental D3 may not mimic all possible beneficial effects of UVR, and uncovering non-D3-mediated mechanisms of UVR tumor inhibition may lead to novel strategies for cancer prevention.”
An important point about vitamin D, sunlight and breast cancer.
Finally, there is no doubt that vitamin D has anticancer benefits. This research however, is especially relevant in that it corroborates what I have said in my soon-to-be-released book, Embrace the Sun. First of all, we must not put all of the benefits of sunlight in the vitamin D box. Secondly, sun exposure performs myriad miracles beyond vitamin D. One of those miracles may be breast cancer prevention and inhibition. Thirdly, if we erroneously believe that we can obtain all of the sun’s benefits from popping a vitamin D pill, we may miss the holistic effects of the sun, which provide a cornucopia of salubrious results.
So, safely (without burning) embrace the sun and ease your mind about breast cancer.
 Anastasia M. Makarova, Flora Frascari, Parastoo Davari, Farzam Gorouhi, Philip Dutt, Lynn Wang, Akash Dhawan, Grace Wang, Jeffrey E. Green, Ervin H. Epstein, Jr. Ultraviolet radiation inhibits mammary carcinogenesis in an ER negative murine model by a mechanism independent of vitamin D3. Downloaded from cancerpreventionresearch.aacrjournals.org on April 12, 2018.
Although liver cancer is generally thought to be related to drinking, other factor such as obesity, HIV infection, smoking, diabetes, socioeconomic factors, drugs and others come into play. A recent study compared sun exposure to liver cancer and adjusted for the aforementioned factors. Sun exposure was shown to be a major factor in reducing the risk of the most prevalent and deadly liver cancer, called hepatocellular carcinoma.
Major finding for liver cancer:
The subjects were divided into five groups, or quintiles, based on their sun exposure. In addition such factors as as outdoor activity, geographical residence, urban or rural settings, etc. were adjusted for.
Most noteworthy, was the fact that for each quintile of increasing sun exposure, there was a 17% decrease in the liver cancer risk.
The only disappointing part to the study was this: The researchers assumed that the positive influence of sun exposure on liver cancer was due to vitamin D production. And, they may have been correct. Yet the sun causes the body to produce many other photoproducts. Due to the sun’s myriad effects, serotonin, endorphin, BDNF, nitric oxide, and dopamine are all increased. Therefore, it is impossible to know if vitamin D alone was the reason for the reduced risk of liver cancer. However, vitamin D undoubtedly played a large part in the positive results. And, there is a problem with giving vitamin D the credit without knowing for sure. People may believe, due to this research, that they need only to take a vitamin D supplement to receive all benefits of sunlight. Therefore, they can make very bad assumptions.
This is the first study on sun exposure and liver cancer.
Probably, this is the first research to show a link between liver cancer and inadequate sun exposure. However, there are indications that sun exposure is associated with a reduced risk of another liver ailment, called fatty liver disease.
In conclusion, if you are a liver lover, you can love your liver by protecting it from liver cancer. Hence, you should obtain your share of unscreened, direct, non-burning sun exposure. Happy sunning!
 Trang VoPham, Kimberly A. Bertrand, Jian-Min Yuan, Rulla M. Tamimi, Jaime E. Hart,
and Francine Laden. Ambient ultraviolet radiation exposure and hepatocellular carcinoma incidence in the United States. Environmental Health (2017) 16:89.
 Gorman S, Black LJ, Feelisch M, Hart PH, Weller R. Can skin exposure to sun prevent liver inflammation? Nutrients 2015 May 5;7(5):3219-39.
A recent sunshine article in the UK online newspaper, The Mail, led with the headline, “Sunshine breaks could mean better mental health.” It then went on to describe how many shift workers, as well as other residents of the UK, are deficient in vitamin D. Quoting from research published in the Journal BMC Public Health, the article stated that about 91% of residents are at least insufficient in vitamin D.
Vitamin D deficiency of that extent is a health crisis, of that there is no doubt. It is also a surety that the way to combat vitamin D deficiency is by taking “sunshine breaks.” However, it is misleading to assume it is vitamin D deficiency that is responsible for the entire problem with mental health and other diseases as they relate to sun exposure. Consider the fact that lack of sunshine deficiency also causes problems beyond vitamin D deficiency. For example, the natural 24-hour cycles, called circadian rhythms, are desynchronized by lack of sunshine in the morning. This causes us to feel out of synch and to be more susceptible to many diseases including cancer.
Sunshine is vital to mental and physical health, and that health is not due to vitamin D alone. Take a holistic view of the importance of sunshine.
 Sowah D, Fan X, Dennett L, Hagtvedt R, Straube S. Vitamin D levels and deficiency with different occupations: a systematic review. BMC Public Health. 2017 Jun 22;17(1):519.
 Lambert GW, Reid C, Kaye DM, Jennings GL, Esler MD. Effect of sun and season on serotonin turnover in the brain. Lancet. 2002 Dec 7;360(9348):1840-2.
 Asta Juzeniene and Johan Moan. Beneficial effects of UV radiation other than via vitamin D production: Dermato-End Holick, M. The UV Advantage 2. Ibooks 2003, New York. Ocrinology 2012;4(2):109–117.
 Holick, M. The UV Advantage 2. Ibooks 2003, New York.
 Molendijk ML, Haffmans JP, Bus BA, Spinhoven P, Penninx BW, Prickaerts J, Oude Voshaar RC, Elzinga BM. Serum BDNF concentrations show strong seasonal variation and correlations with the amount of ambient sun. PLoS One. 2012;7(11):e48046.
By Marc Sorenson, EdD, for sun exposure…
A new research paper on sun exposure and cancer has some interesting observations and some errors. It is entitled, Does Sunlight protect us from cancer? Here is the abstract of the article, verbatim.
“The Ultraviolet (UV) radiation contained in sunlight is a powerful mutagen and immune suppressant which partly explains why exposure to solar UV is the biggest risk factor for the development of cutaneous tumors. Evidence is building that sunlight may be protective against some internal malignancies. Because patients with these tumors are often vitamin D deficient, this has led some to propose that vitamin D supplementation will be beneficial in the treatment of these cancers. However, the results from already completed trials have been disappointing which has given weight to the argument that there must be something else about sunlight that explains its cancer-protecting properties.”
The first sentence, of course, is false. The idea, that sun exposure is the biggest risk factor for skin cancer, is erroneous. We have presented materials many times, proving that melanoma is not caused by sun exposure, and that sun exposure is protective against that disease. And as regards common skin cancers, we have shown that high-fat nutrition, lack of antioxidants, meat consumption and alcohol intake are all risk factors. Search the blogs on this site to read the different articles.
The statement is correct, of course, that sunlight is protective against many internal cancers. Dr. Bill Grant and I are finishing our book, Embrace the Sun, where we present nearly all of the research on the protective influence of sun exposure against cancer.
The statement that vitamin D research has been disappointing is both true and false. Randomized controlled studies (RCTs) have shown the vitamin D supplements do have a protective effect against internal cancers, contrary to the statement by the researchers.
Finally, let’s look at the statement that there is something beyond vitamin D that explains the cancer-protecting properties of sun exposure. That is partially true. Beyond vitamin D, the sun causes the production of nitric oxide, serotonin, endorphin and BDNF, all of which are vital to human health, and may have their own cancer-protective properties.
The bottom line? Eat correctly (avoid junk), REGULARLY soak up some sun around midday and get plenty of exercise. That advice will be a boon to your health in myriad ways.
In a new scientific paper, Dr. MS Razzaque shows that there may be some downsides to vitamin D supplementation, including “cardiovascular events and beyond.” He also states that “since hypovitaminosis D status usually reflects reduced sunlight exposure, the obvious primary replacement should be safe sunlight exposure, and not exogenous supplements.”
The paper specifically mentions that avoiding sunlight exposure may influence the initiation and progression of different types of tumors [cancer], high blood pressure, type 1 diabetes and multiple sclerosis. It also points out that there may be some deleterious consequences of vitamin D supplementation, although in my opinion, the dosage would need to by quite high.
As I have indicated in many of my posts on the Sunlight Institute site, sun exposure is the most natural way to obtain vitamin D, and it has no toxicity, since it is self-regulated.
What wasn’t mentioned was the production of health-promoting substances when sun touches the skin, e.g. endorphins and nitric oxide. And of course, the sun helps the brain to produce serotonin and BDNF, which are critical for proper brain function.
So soak up your sunlight but don’t burn.
 Razzaque MS. Sunlight exposure: Do health benefits outweigh harm? J Steroid Biochem Mol Biol. 2016 Sep 16. [Epub ahead of print].
By Marc Sorenson, EdD. Sunlight Institute… promoting safe sun exposure…
It has long been known that vitamin D deficiency is associated with hypertension. But could that association really be a measurement of inadequate sun exposure? A most interesting investigation was carried out this month (July 2016) in which the researchers evaluated over 1100 subjects from an ongoing study called “the Reasons for Racial and Geographic Differences in Stroke.” They measured vitamin D levels and also assessed sun exposure levels, and found that both high vitamin D levels and high sun exposure levels were associated with higher blood pressure.
What makes this research different is that when the data was adjusted for other factors, high sun exposure was even more impressive as a protective factor against high blood pressure. However, adjusting for vitamin D levels had no effect on the association of sun exposure to lower blood pressure; for each increase in sun exposure, there was a corresponding decrease in blood pressure, but the same was not true for increases or decreases in vitamin D levels.
The researchers made this statement: “We conclude that although 25(OH)D concentration is inversely associated with SBP, it did not explain the association of greater sunlight exposure with lower BP.”
To me, this research indicates that sun exposure directly effects lower blood pressure levels, independently of vitamin D. This is not surprising, since clinical trials of vitamin D supplementation have found only small effects on blood pressure.
I hypothesize that nitric oxide (NO), is the mechanism by which sun exerts its impressive effects. NO is a potent vasodilator, and when it is released into the arteries by UVA stimulation, causes increased blood flow and lowers blood pressure.  Dr. Oplander and his colleagues wrote the first paper on the UVA, NO and blood pressure in 2009, and Dr. Richard Weller has been a leader in doing research and granting interviews on NO since that time. He has made two interesting statements: (1) “We suspect that the benefits to heart health of sun will outweigh the risk of skin cancer. The work we have done provides a mechanism that might account for this, and also explains why dietary vitamin D supplements alone will not be able to compensate for lack of sun.” (2) “Although the benefits of sun are often attributed to vitamin D, a gas called nitric oxide is also important. Made when the sun hits our skin, nitric oxide lowers blood pressure when it enters the bloodstream. Although the reduction is small, it could ‘make a big difference.”
A study from China also demonstrates that exposure to sun correlates to a lowered risk of hypertension. In a randomly selected population of Chinese residents from Macau (where the rate of hypertension is very high), the following risk factors for hypertension were assessed: lack of sun exposure, low intake of fish, smoking, obesity and lack of exercise. An average of more than one-half hour of sun exposure per day compared to none predicted a 40% reduced risk for hypertension.
Vitamin D has many marvelous health effects, but sun exposure per se has many more, because not only does the sun stimulate the production on vitamin D, it also produces other vital photoproducts such as NO, endorphins and serotonin. When we avoid the sun and simply take a vitamin D pill, we are short-changing ourselves for the total package of benefits derived from the sun. And in the case of high blood pressure, we may be receiving almost no benefit from vitamin D. Think about it, and enjoy the sun safely.
 Rostand SG, McClure LA, Kent ST, Judd SE, Gutiérrez OM. Associations of blood pressure, sunlight, and vitamin D in community-dwelling adults. J Hypertens. 2016 Jul 1. [Epub ahead of print]
 Beveridge LA, Struthers AD, Khan F, Jorde R, Scragg R, Macdonald HM, Alvarez JA, Boxer RS. Et. al. Effect of Vitamin D Supplementation on Blood Pressure: A Systematic Review and Meta-analysis Incorporating Individual Patient Data. AMA Intern Med. 2015 May;175(5):745-54.
 Liu D, Fernandez BO, Hamilton A, Lang NN, Gallagher JM, Newby DE, Feelisch M, Weller RB. UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase. J Invest Dermatol. 2014 Jul;134(7):1839-46.
 D Liu, BO Fernandez, NN Lang, JM Gallagher, DE Newby, M Feelisch and RB Weller. UVA lowers blood pressure and vasodilates the systemic arterial vasculature by mobilization of cutaneous nitric oxide stores. Photobiology Abstract # 1247 May 2013.
 Opländer C, Volkmar CM, Paunel-Görgülü A, van Faassen EE, Heiss C, Kelm M, Halmer D, Mürtz M, Pallua N, Suschek CV.. Whole body UVA irradiation lowers systemic blood pressure by release of nitric oxide from intracutaneous photolabile nitric oxide derivates. Circ Res. 2009;105:1031–40.
 Quoted on Mercola.com http://articles.mercola.com/sites/articles/archive/2013/07/15/sun-exposure.aspx accessed July 2, 2015.
 Weller, R. Shunning the sun may be killing you in more ways than you think. New Scientist July 2, 2015.
 Ke L, Ho J, Feng J, Mpofu E, Dibley MJ, Feng X, Van F, Leong S, Lau W, Lueng P, Kowk C, Li Y, Mason RS, Brock KE. Modifiable risk factors including sun exposure and fish consumption are associated with risk of hypertension in a large representative population from Macau. J Steroid Biochem Mol Biol 2013 Nov 1 [Epub ahead of print].
By Marc Sorenson, EdD. Sunlight Institute.
Regular sun exposure is one of the best ways to reduce the risk of many cancers. Although the relationship of sun exposure (and vitamin D) to the risk of prostate cancer is controversial, a study from Australia, published in 2011, showed that the less sun exposure, the greater the risk of the cancer. The researchers investigated the relationship between prostate cancer incidence and solar radiation in non-urban Australia and found an inverse association. There are many other studies that indicate a protective effect of sun exposure. One of the earliest was conducted by Dr. Esther John and her colleagues: they compared the lifetime sun exposure of 450 white men with advanced prostate cancer to that of 455 white men who did not have cancer. The men were divided into quintiles according to the amount of exposure they had received. Subjects in the highest fifth of sun exposure had only 51% of the risk of prostate cancer as did those in the lowest quintile.
Another study on cancer that corroborated these observations was entitled: Is prevention of cancer by sun Exposure more than just the effect of vitamin D? A systematic review of epidemiological studies. In their review, the authors noted that regular sun exposure correlated to a reduced risk of colorectal cancer, prostate cancer, breast cancer and non-Hodgkin’s lymphoma (NHL). However, vitamin D levels correlated to a reduced risk of colorectal, and to a lesser extent, breast cancer, but were not correlated to a significant risk reduction in prostate cancer and non-Hodgkin’s lymphoma. The authors concluded with this statement: “Particularly in prostate cancer and NHL, other sun-potentiated and vitamin D-independent pathways, such as modulation of the immune system and the circadian rhythm, and the degradation of folic acid, might play a role in reduced cancer risk as well.” These researchers did well to remind us, that as important as vitamin D is to the human body, other effects of sun exposure may be more important in some diseases. The authors could have also mentioned the effect of sun on vasodilation, mediated by the production of nitric oxide (produced by the skin after sun exposure). They could also have discussed the influence of sun on production of serotonin and endorphins, all of which may have contributed to their observations.
Other research used childhood sunburn as a measure of UVR exposure and determined that men who had sunburned as children had only about one-fifth the risk of contracting prostate cancer as those who had not sunburned. A note of caution! We are not recommending that anyone sunburn in order to prevent prostate or other types of cancer. Sunburn was used in this research to predict higher vitamin D levels, but it is not necessary to achieve those levels, since non-burning sun exposure achieves the same results. This research also demonstrated that men with lowest level of UVR exposure had more than triple the risk of prostate cancer and that onset of the disease was delayed more than four years in those who had the greatest exposure compared to those who had the least exposure. A follow-up to this study, reported that men in the lowest quartile of sunbathing were linked to a 5.33-fold greater risk of prostate cancer than those in the highest quartile. Still other research has indicated that “higher levels of cumulative exposure, adult sunbathing, childhood sunburn and regular holidays in hot climates were each independently and significantly associated with a reduced risk of this [prostate] cancer.
So men, protect your prostate by regular, non-burning sun exposure. Don’t let the Powers of Darkness frighten you away from the sun.
 Loke TW, Seyfi D, Khadra M. Prostate cancer incidence in Australia correlates inversely with solar radiation. BJU Int. 2012 Apr;109 Suppl 3:75.
 John EM, Schwartz GG, Koo J, Van Den Berg D, Ingles SA. Sun exposure, vitamin D receptor gene polymorphisms, and risk of advanced prostate cancer. Cancer Res 2005;65(12):5470-79.
 van der Rhee H, Coebergh JW, de Vries E. Is prevention of cancer by sun exposure more than just the effect of vitamin D? A systematic review of epidemiological studies. Eur J Cancer. 2013 Apr;49(6):1422-36.
 Moon SJ, Fryer AA, Strange RC. Ultraviolet radiation: effects on risks of prostate cancer and other internal cancers. Mutat Res 2005;571(1-2):207-19.
 Bodiwala D, Luscombe CJ, Liu S, Saxby M, French M, Jones PW, Fryer AA, Strange RC.. Prostate cancer risk and exposure to ultraviolet radiation: further support for the protective effect of sun. Cancer Lett 2003;192:145-49.
Nearly every article written on the addictive influences of sun exposure or other UV exposure takes a negative tack. We need to realize that some addictions are very good for us. Some runners are addicted to getting up every morning and going on the morning run. If one wants to be slim and fit, that is certainly a positive addiction. Hugging my wife is also a positive addiction; her touch helps to heal me and fills me with an addictive love. I’m also addicted to hiking in the pines and aspens near my Nevada ranch. There is little more exhilarating than being at 11,000 feet elevation and breathing the clear mountain air during a hike. You probably have your own positive addictions.
Sun exposure can certainly become an addiction, but is that all bad? In my opinion, no. When done habitually, sunning reduces the risk of melanoma and reduced the risk of myriad harmful diseases. It is therefore a positive and salubrious addiction.
A recent study, somewhat negative in tone, demonstrates that UVB light, contained in both sun lamp radiation and sun radiation, triggers the production of beta endorphins, one of the feel-good chemicals, sometimes called a “reward” chemical, that makes us want more.[i] The researchers used 12 healthy volunteers and used a UVB lamp to deliver a dose of narrow-band UVB light. Skin samples were taken before and after the exposure. After 24 hours, the skin samples showed an increase in endorphin levels in 11 of the twelve subjects.
Sun exposure enhances health. A twenty-year study demonstrated that the risk of death among people who were sun-seekers was only half that of those who received little sun.[ii] The researchers made this statement: “In both models the summary sun exposure variables showed a ‘dose-dependent’ inverse relation between sun exposure and all-cause death.”
Obviously, habitual sun exposure produces a positive addiction, and that is good! God (or nature if you prefer) has programmed our bodies to seek the sunlight in order to help provide a healthful and rewarding life. “Habitual” is the operative word here. An occasional blast of sun that causes burning is definitely not recommended. Be careful and enjoy your positive addictions.
[i] Jussila A, Huotari-Orava R, Ylianttila L, Partonen T, Snellman E. Narrow-band ultraviolet B radiation induces the expression of β-endorphin in human skin in vivo. J Photochem Photobiol B. 2016 Feb;155:104-8.
[ii] Pelle G. Lindqvist, Elisabeth Epstein, Mona Landin-Olsson, Christian Ingvar, Kari Nielsen, Magnus Stenbeck & Håkan Olsson. Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort. J Intern Med. 2014 Jul;276(1):77-86.