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Vitamin D:How much Sun Exposure Do You Need?

Updated: Sep 2, 2021

Vitamin D is a sunlight vitamin that has been produced on Earth for over 500 million years.Vitamin D is only one of the 13 vitamins that the human body can make.Vitamin Dcomes in two forms.

Vitamin D is synthesized in the human body in sufficient quantities if there is enough exposure to sunlight and with a properly associated organ (skin, liver, and kidney) function. A good diet provides enough of all vitamins except D. Humans do not need a vitamin D diet if they are to get enough sunlight.

If you do not get enough sunlight to make the vitamin D you need, and your diet cannot make the rest, you need a supplement.


The process of vitamin D-3 synthesis

In humans, like most mammals, vitamin D3 is created as a photochemically.

This process begins when the ultraviolet energy of the sun acts on the cholesterol (7-dehydrocholesterol) in the skin.The result is provitamin-D3, which is inactive.Before D3 can work, it must go for further conversion to the liver and then to the kidneys. The final product is the active vitamin D, technically known as 1,25-dihydroxyvitamin D or calcitriol.










The process of vitamin D-2 synthesis.

Humans do not make vitamin D2.


Vitamin D2 (ergocalciferol) is produced by invertebrates, some plants and fungi.


The biological production of D2 is induced by ultraviolet light.


Both photosynthetic vitamin D2 (ergocalciferol) in plants and vitamin D3 (cholecalciferol) synthesized in the skin of animals and humans in response to sunlight must go through your liver and kidneys to be converted into the active form of vitamin D.

How much sunlight we need depends on these factors
  • The position of the sun in the sky

  • Time of day, season, latitude

  • Use of sunscreen (SPF 8 or above)

  • Body surface area exposed

  • Cloud cover

  • Air pollution

  • Skin pigmentation

  • Age

How much sunlight is needed
  • Exposure to about 15 minutes of sunlight each day can help prevent vitamin D deficiency.

  • Exposure time required for those with darker skin color increases with respect to skin color level.

  • The ability to make vitamin D appears strong in adolescence and decreases with age.

  • According to Vitamin D researchers, about 5-30 minutes of sunlight between 10 AM and 3 PM at least twice a week on the face, arms, legs or back without sunscreen usually leads to insufficient vitamin D synthesis.

  • Moderate use of commercial tanning beds that emit 2% –6% UVB radiation is also effective.

Be careful with too much sunlight
  • Excessive sun exposure leading to skin cancer is not recommended as there is a risk of ultraviolet radiation.

  • Despite the sun's importance to vitamin D synthesis, it is prudent to limit skin exposure to sunlight and tanning beds from UV radiation.

  • UV radiation is responsible for 1.5 million skin cancers and 8,000 deaths each year from metastatic melanoma in the United States.

  • Lifetime cumulative UV damage to the skin is also more likely to cause some age-related dryness and other cosmetic changes.

Sunlight and Vitamin D:

The dose of UV light is indicated according to a person's skin sensitivity.


Minimum erythema dose (MED), which is the amount of UV radiation that produces minimal erythema (redness caused by sunburn or capillary engorgement) of a person's skin within hours of exposure.


A two-piece swimsuit provides a minimum erythemal dose of 10,000 to 25,000 IU (the amount of sun that the skin begins to turn pink)



References:


  1. Sahay M, Sahay R. Rickets-vitamin D deficiency and dependency. Indian J Endocrinol Metab. 2012;16(2):164-176. doi:10.4103/2230-8210.93732

  2. Office of dietary supplements - vitamin D. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Accessed Jun 27, 2020.

  3. Kift R, Rhodes LE, Farrar MD, Webb AR. Is Sunlight Exposure Enough to Avoid Wintertime Vitamin D Deficiency in United Kingdom Population Groups?. Int J Environ Res Public Health. 2018;15(8):1624. Published 2018 Aug 1. doi:10.3390/ijerph15081624

  4. Publishing HH. On call: Vitamin D2 or D3? Harvard Health Web site. https://www.health.harvard.edu/newsletter_article/vitamin-d2-or-d3. Accessed Aug 23, 2020.

  5. Jacobsen KH. Introduction to health research methods. Sudbury: Jones & Bartlett Learning, LLC; 2016. https://ebookcentral.proquest.com/lib/[SITE_ID]/detail.action?docID=4441620

  6. Nair R, Maseeh A. Vitamin D: The "sunshine" vitamin. J Pharmacol Pharmacother. 2012;3(2):118-126. doi:10.4103/0976-500X.95506

  7. Pilz S, Zittermann A, Trummer C, et al. Vitamin D testing and treatment: a narrative review of current evidence. Endocr Connect. 2019;8(2):R27-R43. doi:10.1530/EC-18-0432

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