Can sitting in the sun help your body produce vitamin D which fights the coronavirus infection?

This article is from Pubmed and is slightly edited for better understanding.

Also, there is a study called 

Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren

Conclusion: This study suggests that vitamin D₃ supplementation during the winter may reduce the incidence of influenza A, especially in specific subgroups of schoolchildren. This trial was registered at https://center.umin.ac.jp as UMIN000001373.

During the winter, or during other times of the year when sun exposure is not a possibility for you, then supplementation with vitamin D3 (cholecalciferol) is an option that should be seriously considered. 

The "final" conclusion is that Vitamin D actually works by increasing your body's production of 2-300 different antimicrobital peptides that are actually far more effective than any synthetic antibiotic or antiviral.

For more info about where to aquire good quality and good price vitamin D3 send me a mail at alexlunaview@gmail.com for further informations. 

Vitamin D is the sunshine vitamin that has been produced on this earth for more than 500 million years. During exposure to sunlight 7-dehydrocholesterol in the skin absorbs UV B radiation and is converted to previtamin D3 which in turn isomerizes into vitamin D3.

Life forms began to evolve in the oceans over 1 billion years ago. They took advantage of sunlight and used it as an energy source to generate carbohydrates

As the industrial revolution swept across Northern Europe in the 1600s resulting in buildings built in close proximity and coal burning causing a pall of air pollution so too appeared a bone deforming disease rickets in children that had devastating health consequences

In 1921 exposed rachitic children to sunlight on the roof of their hospital in New York City and demonstrated significant radiologic improvement in the children’s rickets. These physicians also realized that children of color were at much higher risk for rickets and concluded that they needed longer exposure to sunlight to both treat and prevent rickets.

UV radiation therapy for rickets. (A) Photograph from the 1920s of a child with rickets being exposed to UV radiation. (B) Radiographs demonstrating florid rickets of the hand and wrist (left) and the same wrist and hand taken after treatment with 1 h UV radiation 2 times a week for 8 weeks. Note mineralization of the carpal bones and epiphyseal plates (right). Holick, copyright 2006. Reproduced with permission.

By turn of the 20th century it was estimated that upwards of 80–90% of children living in Northern Europe and in Northeastern United States had evidence of rickets.

Steenbock and Black exposed various foods including cotton seed oil, corn oil, and milk to UVB radiation and demonstrated that this process imparted antirachitic activity for rodents. This led to the addition of ergosterol to milk followed by UVB irradiation or the addition of ergosterol that had been previously exposed to UVB radiation or to the addition of vitamin D to the milk

During exposure to sunlight solar radiation with wavelengths of 290–315 nm penetrate into the skin and are absorbed by proteins, DNA and RNA as well as 7-dehydrocholesterol. Most of this UVB radiation is absorbed in the epidermis and as a result when exposed to sunlight most of the vitamin D that is produced in the skin is made in the living cells in the epidermis. This is the reason why after exposure to sunlight vitamin D remains in the skin even when the skin is washed with soap and water immediately after the exposure to sunlight.

There has been a lot of discussion as to whether ingesting vitamin D from the diet or from a supplement is the same as producing vitamin D in the skin. Because it takes approximately ~8 h for previtamin D in the skin to fully convert to vitamin D and it takes additional time for the vitamin D to enter the dermal capillary bed this is at least 2 of the explanations for why it was observed that vitamin D produced in the skin last 2–3 times longer in the circulation when compared with ingesting it orally.

Plasma vitamin D or vitamin D after UV light exposure or vitamin D oral dosage.

No matter how much sun a human is exposed to vitamin D intoxication will not occur because any excess previtamin D and vitamin D is photodegraded into products that have no calcemic activity. This however does not mean that these myriad of photoproducts don't have other biologic effects such as regulating epidermal cell growth and reducing risk of skin cancer. One product, lumisterol if converted to 1,25-dihydroxylumisterol may have anti-tumor effects in the skin.

Some of the suprasterols also have antiproliferative activity in cultured human keratinocytes. Therefore sensible sun exposure to produce previtamin D, vitamin D and its photoproducts may have some additional benefits above and beyond simply taking a vitamin D supplement or ingesting vitamin D from dietary sources.Therefore sensible sun exposure to produce previtamin D3, vitamin D3 and its photoproducts may have some additional benefits above and beyond simply taking a vitamin D3 supplement or ingesting vitamin D3 from dietary sources.

Only about one percent of solar UVB radiation ever reaches the earth’s surface even in the summer at noon time. The reason is that all of the UV C (200–280 nm) and all of the UVB radiation up to approximately 290 nm is efficiently absorbed by the stratospheric ozone layer.

In addition the ozone layer absorbs approximately 99% of the UVB radiation with wavelengths 291–320 nm. Therefore increasing the path length by which solar UVB has to travel through the ozone layer will result in a decrease in the number of UVB photons that reach the earth's surface (Fig. 22).

This is the explanation for why during the winter when living above and below approximately 33° latitude very little if any vitamin D can be produced in the skin from sun exposure. People who live farther North and South often cannot make any vitamin D in their skin for up to 6 mo of the year.

For example in Boston at 42° North essentially no vitamin D can be produced in the skin from November through February. Inhabitants living in Edmonton Canada at 52° North, Bergen Norway at 60° North, or Ushuaia Argentina at 55° South are unable to produce any significant vitamin D for about 6 mo of the year.

In the early morning and late afternoon the zenith angle of the sun is also more oblique similar to winter sunlight and as a result very little if any vitamin D can be produced in the skin before 10 a.m. and after 3 p.m. even in the summer time

Conversion rate of 7-dehydrocholesterol (7-DHC) to vitamin D depending on time of the day and season in Boston (42° North). The measurements were conducted after exposing ampoules filled with 7-DHC to sunlight. Holick, copyright 2013, reproduced with permission.

Air pollution including nitrous oxide and ozone is common in many large cities including Los Angeles and San Diego and will absorb solar UVB radiation and therefore reduce the effectiveness of sun exposure in producing vitamin D in the skin.

Since glass absorbs all UVB radiation, exposure of the skin to sunlight that passes through glass, plexiglass, and plastic will not result in any production of vitamin D in the skin.

People have a feeling of wellbeing when exposed to sunlight. This may be due to the fact that keratinocytes produce β-endorphin when exposed to UV radiation.

In the early 1900s Finsen (F observed that exposure to sunlight dramatically improved cutaneous skin lesions caused by a tuberculosis infection (lupus vulgaris) and received the Nobel Prize in 1903 for his enlightening observations. This led to the use of solariums as a way to treat patients with tuberculosis and gave rise to the use of heliotherapy to improve health.

Heliotherapy was used to treat a wide variety of chronic illnesses in the early 1900s and it is still practiced throughout the world and especially in Northern Europe. The rise in the use of pharmaceuticals to treat acute and chronic diseases led to the demise of heliotherapy especially in United States.

One of the first association studies relating sun exposure with reduced risk for cancer was reported in 1916 by Hoffman, who found that living at a higher latitude was associated with an increased risk for mortality from cancer. He compared cancer mortality between 1908 and 1912 and observed that cancer mortality increased with increasing distance from the equator

There are a variety of association studies demonstrating that being born or living near the equator reduces risk of several autoimmune diseases.

Schizophrenia has been associated with inadequate sun exposure and vitamin D deficiency

The vitamin D status seems to influence the risk for an influenza infection respectively vitamin D supplementation has proven to decrease the risk for influenza infection.

For almost 100 y a variety of strategies have been used to treat and prevent vitamin D deficiency especially in children. From 1930 through 1950s parents purchased a lamp at their local pharmacy that emitted vitamin D producing UVB radiation

Children wearing eye protection had their arms, abdomen and legs were routinely exposed to a UV emitting lamp several times a week

In Russia children in school in wintertime were routinely exposed to a mercury arc lamp placed in the center of the school room that emitted UVB radiation to prevent vitamin D deficiency rickets

Sensible sun exposure can also be an excellent source of vitamin D for both children and adults. Because foods contain very little vitamin D it is difficult to obtain enough vitamin D from dietary sources even when consuming foods fortified with vitamin D.

Skin pigmentation or the lack thereof was important in the evolution of humans as they migrated North and South of the equator. Africans such as the Maasai living outdoors exposed to sunlight daily throughout the year have robust circulating concentrations of the major circulating form of vitamin D, 25(OH)D, in the range of 46 ng/mL.

Our ancestors routinely worshiped the sun for its life giving properties.

It is curious that some of the earliest photosynthetic life forms for more than 500 million years have been producing vitamin D and that throughout evolution most vertebrates including humans have depended on sun exposure for their skeletal health.

The driver for the evolution of hypopigmented humans i.e., Caucasians is likely due to the need to have more vitamin D producing solar UVB radiation to penetrate into the skin to produce vitamin D.

Females born with vitamin D deficiency and suffering from infantile rickets resulted in them having a flat pelvis and a small pelvic outlet. These females although fertile would have had a difficult time, if not impossible, to give vaginal birth resulting in both maternal and fetal death.

Indeed it was because of the vitamin D deficiency pandemic in late 1800s that Cesarean sectioning became common practice for the delivery of healthy children of mothers who had suffered from vitamin D deficiency in utero and during their first few years of life.

Vitamin D deficiency in pregnant women today is still associated with a 400% increase in the predicted probability for a Cesarean section.

Over the past four decades with very little thought as to its consequences, several national and international health organizations have condemned any direct sun exposure. The American Academy of Dermatology has taken the extreme position of recommending that no one should ever be exposed to direct sunlight without sun protection. This radical view of sunlight and UVB radiation has led to its designation as a carcinogen. To suggest that one should never be exposed to sunlight because excessive exposure to sunlight is linked to an increased risk for non-melanoma skin cancer is like suggesting that because breathing 100% oxygen can cause lung damage and death, that no one should breath an atmosphere that contains 20% oxygen.

The lack of appreciation of the importance of sensible sun exposure for providing children and adults with their vitamin D requirement has led to a worldwide vitamin D deficiency pandemic.

Reports from Mexico, South America, Europe, Asia, India and even Africa suggest that more than 50% of the world population is at risk for vitamin D deficiency.

Even in Australia, the skin cancer capital of the world, it is now recognized that the slip, slap, slop message has led to more than 40% of the population being vitamin D deficient.

The CDC concluded that vitamin D deficiency is becoming more prevalent in the US because of obesity, decrease in the consumption of vitamin D fortified milk and increased sun protection.

Sensible sun exposure which is free, eating foods that naturally contain vitamin D or are fortified with vitamin D as well as taking a vitamin D supplement should guarantee vitamin D sufficiency.

There is no downside to increasing vitamin D intake and there could be a substantial upside, i.e., improvement not only of musculoskeletal health but overall health and welfare. It has been estimated that as much as 25% of health care dollars could be saved just by improving the world’s vitamin D status.

The H1N1 "Spanish flu" outbreak of 1918-1919 was the most devastating pandemic on record, killing between 50 million and 100 million people. Should the next influenza pandemic prove equally virulent, there could be more than 300 million deaths globally. The conventional view is that little could have been done to prevent the H1N1 virus from spreading or to treat those infected; however, there is evidence to the contrary. Records from an "open-air" hospital in Boston, Massachusetts, suggest that some patients and staff were spared the worst of the outbreak. A combination of fresh air, sunlight, scrupulous standards of hygiene, and reusable face masks appears to have substantially reduced deaths among some patients and infections among medical staff. We argue that temporary hospitals should be a priority in emergency planning. Equally, other measures adopted during the 1918 pandemic merit more attention than they currently receive.