Benefits Of Sunlight

The sun has been a central part of our society since the dawn of civilization, and we hear so much about it. There are incredible benefits to sunlight but there is a lot of information out there about how it can also be damaging. This article will try and guide you through all the important information you need to know about sunlight.

About sunlight

This might seem like an unnecessary question but, what is sunlight? Sunlight is a mixture of different parts of the electromagnetic spectrum, which is a range of different frequencies and wavelengths of radiation.¹ Sunlight is composed of visible light, infrared (IR) and ultraviolet (UV). This is then emitted around the sun’s circumference and can reach Earth.² The sun’s energy is generated through a process called nuclear fusion, this can only happen when temperatures and pressure are extremely high such as in the inner core of the sun. In the sun this energy is formed by fusing four hydrogen nuclei into one helium nucleus, but because the helium has less mass than the hydrogens the energy is released. The energy leaves the sun and is emitted as solar rays or as a photon of electromagnetic radiation.³ The length of this photon will determine whether it is visible light, IR, or UV. Solar radiation in the UV segment can be further divided into 3 subcategories: UVA, UVB and UVC. However, as most people will know the earth is surrounded by a layer of ozone, this prevents UVC from reaching the earth so the majority of UV light we get is roughly 90% UVA and 10% UVB.⁴

Benefits of sunlight

• Improving Cognitive Function -. Cognitive function is an umbrella term that encompasses multiple brain activities such as: learning, reasoning, thinking, and remembering. A study compared same day exposure to sunlight to a 2-week period through a cognitive test and found that candidates that had a longer term exposure to sunlight had improved cognitive function.⁵
•  Improves our mood - It can also be said that the sun improves our mood., which is regulated by hormones such as serotonin and melatonin. These hormones are in close association with the suprachiasmatic nucleus (SCN) in the brain, which responds to light stimuli.⁶ The SCN is housed within the hypothalamus with connections to the retinas. Within periods of darkness, the SCN will release melatonin from the pineal gland to initiate sleep meaning that more melatonin is released in the winter months. Melatonin is the main hormone involved in monitoring the sleep/wake cycle and the circadian rhythm.⁷ Meanwhile serotonin can be seen as the “happy” drug in our brain, which regulates mood and is a prime target for many antidepressant therapies.⁸ These hormones are linked as melatonin is produced from a 2-step metabolism process of serotonin, and both need the amino acid tryptophan as their starting material.⁹

Seasonal Affective Disorder (SAD) is a condition characterized by depressive episodes that coincide with the darker winter months especially in countries in the northern latitudes.¹⁰ A study has hypothesized that excessive melatonin production may be at fault for people with SAD. Both serotonin and melatonin need tryptophan for their production, but melatonin is secreted from the pineal gland, which lies outside the blood brain barrier (BBB) and serotonin comes from serotonergic neurons (SN) within it. This basically means that the pineal gland will have a continuous supply of tryptophan. The story for SN is slightly different as they lie within the BBB so that the tryptophan has to be transported to them. However, it is not the only amino acid that wants to do this, which means its ability to be transported is directly linked to its availability within the blood. How can the concentration of tryptophan be reduced? Well, a hypothesis is that with SAD more melatonin is produced as there is less light in the day with a resulting lower amount tryptophan being available for serotonin production. This explanation is quite reductive but could create a direct link between exposure to light and an increase in mood. Another positive indicator for this theory is that Bright Light Therapy (BLT) works in 60% of SAD patients to overcome their symptoms.

• Vitamin D Metabolism and Calcium Reabsorption - Sunlight, in particular UVB, is essential for the metabolism of vitamin D to its active form.¹¹ Vitamin D receptors are found in essentially every tissue in the body, such as the skeleton. It has been found to prevent conditions such as rickets and osteomalacia as well as potentially preventing fracture formation. Most hypotheses believe that this is due to increasing calcium and phosphorus in the circulation by promoting intestinal absorption. However, a recent study has postulated that vitamin D might have a direct effect on cartilage and bones, allowing normal development and growth.¹² 
• Other Benefits - 

• On islet cells - Furthermore, the beta islet cells in the pancreas, which are responsible for the secretion of insulin, contain vitamin D receptors. A study has shown that a shortage of Vitamin D in the blood could lead to insulin resistance. Therefore, it has been proposed that giving Vitamin D to pre-diabetic patients could improve their prognosis and prevent the manifestation of diabetes. 
• On tumour formation - Quite amazingly vitamin D has also been linked to preventing tumor formation or slowing down metastasis. The way in which it can do this is quite varied, but to summarize vitamin D can inhibit tumor growth factors, induce apoptosis (cell death) of neoplastic cells and prevent tumors from growing a blood supply.¹² 
• On the heart - The cardiovascular system is another body system which expresses vitamin D receptors. It has been found that in patients with low vitamin D hypertrophic cardiomyopathies were more common. This is a condition in which the heart thickens and stops working properly. However, no studies have been done on the use of vitamin D to prevent cardiac disease. 
• On the Immune System - Another important effect of vitamin D on the body is on the immune system.¹² The innate immune system in particular is affected by vitamin D. This subset of immunity can be described as the defense line you are born with.
• On the blood pressure - There have been associations with sunlight and the release of nitric oxide in the body. When UVA hits the skin, it leads to the release of nitric oxide from the circulation. This is an incredible benefit as it allows the vessels to vasodilate, or increase in size, this decreases the peripheral resistance in the vessels thereby lowering blood pressure. Therefore, it could be said that if you are suffering from high blood pressure you might want to soak up some more rays!

Side effects of sunlight

The previous section has focused on the positive effects of exposure to sunlight, but as many of you will be aware, sunlight can also have negative implications for our health. This is in particular related to extended exposure with activities such as sun-bathing and tanning. Before the industrial revolution most people would be exposed to light on a daily basis and the skin would be adapted to protect them against their continuous exposure Nowadays, particularly in Western culture, there is the trend of seeking sun-filled vacations to compensate for the mainly indoor life most people lead. This short, high-intensity exposure to higher levels of UV radiation can predispose them to various health concerns.¹³

•   Cancers - The 2 main cancers of the skin that UV light can cause include cutaneous malignant melanoma (CMM) and non-melanoma skin cancer (NMSC) ¹³. NMSC is usually caused by increased exposure to sunlight but is not a fatal condition. On the other hand, CMM is much more dangerous and seems to be predisposed in people with sun overexposure. A study found that people using solariums for tanning were at a 20% increased risk of developing CMM. Interestingly enough in a study people were split up into groups of low sun exposure, medium sun exposure and high sun exposure. Every individual had CMM, and it was found that people in the low sun exposure group had a 40% increased risk of sadly passing away¹³. This might mean that sunlight could help prevent mortality in people afflicted with CMM.
• Photoaging - Sunlight also predisposes people to something called photoaging and photo-aggravated dermatosis. Photoaging can be described as premature aging of the skin due to chronic exposure to sunlight¹⁴. People with fair skin seem to be predisposed as they do not have protective pigment melanin. Some symptoms include loss of elasticity and hyperpigmentation. Some photo-aggravated dermatoses include eczema and psoriasis, these are conditions which are worsened by exposure to sunlight.¹⁵
• Eye Damage - There has always been a connection between eye conditions and radiation from the sun. These conditions mainly included acute light damage to the eyes in terms of sunburns on the eyelids. Recently more associations have been made between chronic sunlight exposure and ocular diseases such as cataracts.

FAQs

How much sunlight is enough?

This sadly is not an easy question to answer as it varies depending on different factors such as where in the world you are and your skin tone.¹⁶ But it could be said that at least 30 minutes in the sun could be enough to improve both your physical and mental health.

Which time of the day can we get the best benefit?

Studies have shown that 12pm is the best time to go out in the sun and recharge! This is because it seems to be related to the lowest report of CMM but still allows you to get all the benefits you need.¹⁷

What happens if we don’t get sunlight?

Not only can this have serious impacts on your mental health and cause things like SAD but can lead to negative physiological responses such as rickets and osteomalacia. This is because the body is not able to convert vitamin D into a usable product leading to bony changes and a variety of other problems listed above.

Is it good to look at the sunlight?

Avert your gaze! Acute sunlight damage can include burns to your eyelids and predispose you to skin cancers. In addition, chronic exposure of radiation to your eyes can lead to conditions such as cataracts and pterygium (a growth of the conjunctiva that extends into the cornea).¹⁸

Summary

Hopefully by now you will have a much better understanding of what sunlight is and why it is so important to our health. Not only can it boost your mood and prevent conditions such as SAD, but it is vital for the activation of vitamin D and the release of nitric oxide, which are both essential for bodily functions, such as skeletal repair and lowering blood pressure. Of course, exposure to sunlight can also have its negative implications, such as predisposing to some skin cancers, but this can be avoidable by limiting your experience and by not using tanning salons. Like with most things if you are concerned about your health, please do not hesitate to contact your healthcare provider.