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The Sun -

The Sun is the star at the center of the Solar System. The most important source of energy for life on Earth, this near-perfect sphere of hot plasma is 150 million km (93 million mi) away from us. Yet on some days, it looks and feels as if it's just hanging in the sky... and that can be a good thing, and a bad thing.

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Ultraviolet radiation -

Sunlight reaches the Earth in the form of ultraviolet (UV) radiation. Sunlight has both positive and negative health effects.

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Vitamin D -

The UV in sunlight is a principal source of vitamin D. When your skin is exposed to sunlight, it makes vitamin D from cholesterol. Vitamin D, known as the sunshine vitamin, has many roles in the body and is essential for optimal health. 

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Calcium and phosphate levels -

Vitamin D helps regulate the amount of calcium and phosphate in the body. These factors are vital for maintaining healthy bones and muscle. Vitamin D may also protect against respiratory infections, cognitive decline, dementia, and more.

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Mood boost -

Another benefit of UV exposure is improvement in mood. The Sun's rays provide warmth and light that enhance your general feeling of well-being. Sunlight can also stimulate blood circulation, which boosts energy levels.  

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How much sun? -

The World Health Organization (WHO) states that five to 15 minutes of casual Sun exposure of hands, face, and arms two to three times a week during the summer months is sufficient to keep your vitamin D levels high.

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Sleep-wake cycle -

Sun exposure is associated with the timing of melatonin synthesis. Melatonin is a hormone that regulates the sleep–wake cycle. Sunlight is also responsible for the maintenance of normal and robust circadian rhythms—a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours.

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Exposure to sunlight can help prevent obesity -

The UV in sunlight not only supplies the body with vitamin D, but is also a vital source of nitric oxide, which is imperative to the human body as a tool for regulating important physiological processes including blood circulation and metabolism. Proper exposure to nitric oxide from the Sun will help keep your metabolism running smoothly and discourage overeating.

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Reduced risk of seasonal affective disorder -

Regular exposure to Sun can reduce the risk of seasonal affective disorder (SAD).

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What is seasonal affective disorder? -

SAD is a mood disorder–a seasonal depression or winter depression the symptoms of which usually occur during the fall and winter months when there is less sunlight.

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"Winter blues" -

Sometimes referred to as the "winter blues," SAD has been linked to a biochemical imbalance in the brain prompted by shorter daylight hours and less sunlight in winter. Symptoms–which include sleeping too much, having little to no energy, and overeating–can be distressing and overwhelming, and can interfere with daily functioning. The condition in the summer can include heightened anxiety.

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Depression -

If you’re a woman, it is 200% more likely that you will develop SAD than the average male, according to studies. The average age of onset of SAD is between 18 and 30 years of age. Interestingly,  SAD is nearly non-existent in people over the age of 60.

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SAD treatment -

Treatments for classic (winter-based) seasonal affective disorder include light therapy (pictured), which involves sitting in front of a light therapy box that emits very bright light (and filters out harmful UV rays). It usually requires 20 minutes or more a day, typically first thing in the morning, during the winter.

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Healthy tan? -

Healthy tan? There's no such thing, no matter to what degree. While you're roasting on the beach, the skin produces a dark-colored pigment, melanin, as a shield against further damage from UV radiation. However, it is no defense against long-term UV damage such as skin cancer. A suntan may be cosmetically desirable, but, in fact, it is nothing but a sign that your skin has been damaged and has attempted to protect itself.

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Dangers of long-term exposure to sunlight - Long-term sunlight exposure is known to be associated with a number of negative health issues.

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Skin cancer -

Skin cancers are cancers that arise from the skin, and more than 90% of cases are caused by exposure to UV radiation from the Sun.

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Melanoma -

The rarest but most dangerous type of skin cancer is melanoma. The primary cause of melanoma is UV exposure in those with low levels of the skin pigment melanin. Those with many moles, a history of affected family members, and poor immune function are at greater risk.

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Dark-skinned? -

Dark-skinned people still need to adopt caution under strong sunlight. Compared to fair-skinned people, dark-skinned people have a much lower risk of developing melanoma or non-melanoma skin cancers. They can safely tolerate relatively high levels of UV radiation without getting burnt. But—regardless of skin color—the risk of eye damage and of harmful effects on the immune system remains, according to advice issued by the WHO.

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Skin aging - Overexposure to the Sun is associated with the development of skin aging, a process technically termed photoaging. Attributed to continuous, long-term exposure to UV radiation, early symptoms of photoaging include the appearance of wrinkles around the eyes, mouth, and forehead, and loss of color and fullness in lips.

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Immunosuppression -

One of the most significant effects of prolonged exposure to the Sun is UV-induced immunosuppression, a defective immune response triggered by UV radiation affecting the skin first, and then the whole body.

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Cataracts -

While cataracts are most commonly due to aging, prolonged exposure to sunlight, among other causes, can also lead to a clouding of the eye lens and a subsequent decrease in vision.

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Photosensitivity -

A small percentage of the population have a skin condition that makes them particularly sensitive to the Sun's UV rays. Known as photosensitivity, a minimal dose of UV radiation is sufficient to trigger an allergic reaction leading to rash or severe sunburn. A more general ailment, polymorphic light eruption is a fairly common skin rash triggered by exposure to sunlight or artificial UV light.

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Sunburn -

The most obvious result of overexposure to UV radiation from the Sun is sunburn. Signs and symptoms include pinkness or redness of skin, and pain, tenderness, and itching. More prolonged exposure can cause the skin to swell and blister. Headache, fever, nausea, and fatigue can set in if the sunburn is severe.

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Avoiding sunburn -

Sun protective measures including sunscreen and protective clothing are generally accepted to prevent sunburn and some types of skin cancer. Children are particularly susceptible to sunburn and protective measures should always be used to prevent damage.

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Snow blindness -

Bright sunlight can induce snow blindness, or photokeratitis. This is a painful eye condition caused by exposure of insufficiently protected eyes to UV rays from either intense sunlight or artificial sources, including the electric arc of a welding tool. The reflection off snow and ice serves to increase the intensity of the UV rays.

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The health dangers of not getting enough sunlight -

Lack of sunlight can lead to a deficiency in vitamin D. This can lead to a wide range of health issues, including increased risk of osteoporosis, heart disease, some cancers, infectious diseases, and even the flu, according to the Harvard School of Public Health.

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Heart disease -

Research suggests that vitamin D deficiencies in men caused by sunshine deficit make them twice as likely to develop heart disease.

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Lack of sunlight can impair a child's vision -

Children who spend more time outside reduce their risk of myopia, or nearsightedness. Myopia develops in youngsters when the lens stops compensating for continued growth of the eye. People who had been exposed to higher levels of UV radiation—a factor that's closely related to how much time a person spends outdoors and is exposed to sunlight—as teens and young adults were less likely to be nearsighted at age 65 than those who had been exposed to lower levels of UV radiation.

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Least sunniest place on Earth -

UN climate records indicate that Tórshavn, the capital and largest city of the Faroe Islands, gets an annual average of just 840 hours a year of sunshine, making it the least sunniest destination on the planet.

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The sunniest place on Earth -

According to the World Meteorological Organization, Yuma (pictured) in Arizona is the sunniest place on Earth. The destination has a total of 11 hours of sunlight in winter and up to 13 in summer. This means Yuma experiences an average of 4,015 hours of sunshine per year.

See also: Explore the world's darkest and most sunlit cities

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