This article was originally published as a guest editor post at foodpharmacy.se
I moved to Sweden from the U.K. and arriving in April I was met with an interesting sight. As soon as the sun popped out, people would pose like statues, their faces facing the sun and their eyes shut. Leaning onto walls in the middle of the street, on top of a bridge, at the bus stop. I wondered what the hell are they doing? It took but one year of darkness, and the upcoming April I was standing there like the rest of them.
Our worship of the sun isn’t limited to its role as a symbol for the coming of summer, nor to the fact that it’s essential to our survival by bringing life into plants and animals, that we eat. I believe many with me can agree that they simply feel good when they’re exposed to the sun. As we shall see, there are several reasons for this.
Until now it hasn’t been problematic for our species, evolutionary speaking, to be dependent on sun exposure for important biological functions, since indoor life is a new phenomenon and a lack of sun exposure hasn’t been an issue for the vast majority of mankind. Humans colonised the far northern hemisphere some 4 000-30 000 years ago (depending on location), but that’s not considered very long in evolutionary terms. Also, those populations were exposed to the sun half of the year, whereas us modern Homo sapiens tend to spend a huge chunk of our time indoors in the summer as well. Let’s have a look at how we’re affected by those golden rays.
The Sunshine Vitamin
The most well-known effect of sun exposure is vitamin D production. It’s a hormone-like cholesterol derivative that we can also get through our diet (fatty fish mostly, like salmon). Vitamin D is not actually made in our skin, but a precursor is produced from cholesterol with ultraviolet B (UVB) exposure, which then travels to the liver for modification and is transformed into the active form called calcitriol, mainly in the kidneys. This molecule controls the use of hundreds, maybe thousands of genes, a whopping 3% of our genome. (1, 2) Many of these genes are involved in optimising our immune system by 1) helping it fight infections and cancer and 2) keeping the immune system under control by preventing it from overreacting, thus limiting autoimmune disease. (2)
The importance of this molecule cannot be stressed enough. Vitamin D deficiency correlates with virtually every type of immune-related disorder there is (including cancer, autoimmune disease, cardiovascular disease, metabolic disease and depression) where the link has been investigated scientifically. Also, vitamin D is essential for mineral balance and to avoid osteoporosis, a serious disease causing weakening of the bones. These conditions are more common in people self-reporting to stay out of the sun, and/or who live further away from the equator. Correlation studies warrant caution: a mere epidemiological association does not imply causation. However, the observed connection between vitamin D and chronic disease and inflammation is supported by experimental evidence – a higher level of evidence. This means that disease risk, symptoms or clinical markers have been shown to improve in humans or animals that get vitamin D or are exposed to UV radiation. (2, 3, 4)
Nitric Oxide – The New Kid On the Block
When UVA hits our skin, nitric oxide (NO) is made. NO has traditionally been viewed as a free oxygen radical, a damaging molecule. But NO also has important functions in relaxing and dilating our blood vessels. Some researchers suggest that UV-induced NO has the same effect. In accordance, NO from sun exposure seemingly leads to a reduction in blood pressure, according to some pioneering studies. Formation of NO is the reason beetroot juice and arginine supplementation can be so powerful in alleviating hypertension. Further, some researchers suggest that NO can kill infectious microbes and tumor cells, promote wound healing, and also works as a neurotransmitter. Early studies support the idea that many of the positive effects we see of sun exposure is not, in fact, vitamin D dependent, but can be attributed partly to NO. (5, 6)
Endorphins and Serotonin Relieve Stress and Pain and Enhances Mood
Sun exposure has been linked to a heightened mood, relaxation and reduced tension. When skin cells are exposed to UV radiation, beta-endorphins get released into the blood, possibly in levels that affect our brains and well-being. Beta-endorphins are formed by neurons and exert stress-reducing and pain-lowering effects. Our nervous system also produces serotonin, a production which is increased with sunlight exposure of the skin and the eyes. Serotonin is a neurotransmitter that has many effects, including increasing a sense of calm and joy. Fibromyalgia sufferers report lower pain after UV radiation, and depression is also improved by sun exposure. The mood boost and analgesic effects might be partly due to beta-endorphins and serotonin, and partly to vitamin D. (1, 7-9)
A Lack of Daylight Impairs Circadian Rhythm
Exposure of the eyes to light also affects melatonin secretion. Melatonin is our sleep hormone, usually secreted at a specific daily rhythm, with low levels at daytime and a peak around midnight. When and how much is influenced by the amount of exposure to light during the day. Our circadian rhythm is very important not only for sleep, but also for our metabolic health and our risk of cancer and cardiovascular disease. Melatonin is also an antioxidant with anti-carcinogenic effects. (1, 10)
Sun Exposure Lowers Our Risk of Suffering and Death
You may find this subheading somewhat provocative. However, it is essentially true. As we’ve learned, sun and vitamin D lowers risk of inflammatory conditions of all thinkable kinds. Furthermore, many skin conditions (eczema, vitiligo, psoriasis and more) improve upon sun exposure or UV therapy, through many suggested mechanisms. Also, the risk of a long list of cancer types is seemingly lower in those who are exposed to more sun. (3, 10, 11) The risk of a long list of cancer types… Please take a moment to contemplate this fact.
Findings are not unanimous (research seldom is) but overall, studies of different types point toward a protective role of sun exposure and/or vitamin D levels when it comes to cancer. These studies involve both observational and experimental studies. One review concludes: “The UVB–vitamin D–cancer hypothesis has considerable supporting scientific evidence from a variety of study types: geographical ecological, observational, and laboratory studies of mechanisms, as well as several clinical trials. At this time, the general public and individual physicians can spend more reasonable time in the sun and use vitamin D3 to prevent and treat many cancers.” (11)
Vitamin D is also associated with a lowered all-cause mortality. The risk of death is inversely correlated with the concentration of vitamin D in the blood, up to a certain level. Vitamin D deficiency is not only a risk factor for increased mortality per se, but vitamin D supplementation may also reduce mortality. (1)
Overall, the diverse effects of the sun on our health is striking. I wouldn’t be surprised if new, currently unknown mechanisms of sun-derived biological effects will be uncovered in the years to come. Caution is warranted: consensus is that we strictly must avoid burning the skin, and be moderate regarding our sun exposure. UV radiation also degrades folate, so please ensure sufficient folate intake during the summer months. (1, 2) However, if you’re staying out of the sun to protect yourself from skin cancer, you might want to rethink your strategy and consider your health on the whole. Also, if you’re trying to replace the sun with vitamin D supplementation, be aware of the many other benefits you miss out on. Maybe you’ve heard of the classic ladder of basic human needs. Perhaps it’s time we update that list to air, food, water, shelter, and sun.
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You find the other articles in the 7 part series ”For king and country – Tend to your immune system” here: