Original article
Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes

https://doi.org/10.1016/j.jaad.2009.07.028Get rights and content

Background

The relationship between oral vitamin D supplementation and cutaneous photosynthesis is not well understood.

Objective

We sought to provide estimates of the equivalency of vitamin D production from natural sun exposure versus oral supplementation.

Methods

Using the FastRT simulation tool, we determined sun exposure times needed to achieve serum vitamin D3 concentrations equivalent to 400 or 1000 IU vitamin D for individuals of various Fitzpatrick skin types living in Miami, FL, and Boston, MA, during the months of January, April, July, and October.

Results

Peak ultraviolet B irradiation for vitamin D synthesis occurs around 12 pm Eastern Standard Time (EST). In Boston, MA, from April to October at 12 pm EST an individual with type III skin, with 25.5% of the body surface area exposed, would need to spend 3 to 8 minutes in the sun to synthesize 400 IU of vitamin D. It is difficult to synthesize vitamin D during the winter in Boston, MA. For all study months in Miami, FL, an individual with type III skin would need to spend 3 to 6 minutes at 12 pm EST to synthesize 400 IU. Vitamin D synthesis occurs faster in individuals with lighter Fitzpatrick skin types. The duration to attain 1000 IU of vitamin D is longer in all scenarios.

Limitations

Results of the computer model are only approximations. In addition, calculations were made based on the assumption that ¼ of 1 minimal erythema dose directed at ¼ body surface area is equal to 1000 IU of oral vitamin D.

Conclusions

Although it may be tempting to recommend intentional sun exposure based on our findings, it is difficult, if not impossible to titrate one's exposure. There are well-known detrimental side effects of ultraviolet irradiation. Therefore, oral supplementation remains the safest way for increasing vitamin D status.

Section snippets

Methods

For this study, we used the previously validated FastRT simulation tool and associated vitamin D calculations.8, 10, 11 FastRT is based on look-up tables of simulated atmospheric transmittances for selected scenarios. This simulation tool8 was used along with a recently published Commission Internationale de L'Eclairage vitamin D–effective action spectrum12 (Fig 1) to determine both ultraviolet (UV) B (UVB) irradiances (http://nadir.nilu.no/∼olaeng/fastrt/fastrt.html) and exposure times (//zardoz.nilu.no/~olaeng/fastrt/VitD_quartMEDandMED.html

UVB radiation

Fig 2 demonstrates changes in UVB irradiance in Boston, MA, and Miami, FL, during the months of January, April, July, and October, between the hours of 9 am and 5 pm EST. The UVB irradiance is highest around 12 to 1 pm EST compared with other times of day, in the summer months compared with winter months, and in Miami, FL, compared with Boston, MA.

Vitamin D equivalencies

Table I, Table II (available at www.eblue.org) show the estimated amount of time required to synthesize the oral equivalent of 400 and 1000 IU

Discussion

Sources of vitamin D include foods, supplements, and UVB-mediated cutaneous synthesis. Endogenous vitamin D production requires UV exposure from the sun, a well-known environmental cause of skin cancer.20 Current guidelines by the American Academy of Dermatology and the International Agency for Research on Cancer (IARC), a branch of the World Health Organization, do not recommend intentional unprotected sun exposure as a vitamin D source.4, 21 However, intentional sun exposure has been

References (40)

  • Working Group of the Australian and New Zealand Bone and Mineral Society, Endocrine Society of Australia and Osteoporosis Australia. Vitamin D and adult bone health in Australia and New Zealand: a position statement

    Med J Aust

    (2005)
  • E. Brender et al.

    JAMA patient page: vitamin D

    JAMA

    (2005)
  • M.F. Holick

    The UV advantage

    (2004)
  • A.R. Webb et al.

    Calculated ultraviolet exposure levels for a healthy vitamin D status

    Photochem Photobiol

    (2006)
  • A.R. Webb et al.

    Ultraviolet exposure scenarios: risks of erythema from recommendations on cutaneous vitamin D synthesis

    Adv Exp Med Biol

    (2008)
  • O. Engelsen et al.

    Fast simulation tool for ultraviolet radiation at the earth's surface

    Opt Eng

    (2005)
  • O. Engelsen et al.

    Daily duration of vitamin D synthesis in human skin with relation to latitude, total ozone, altitude, ground cover, aerosols and cloud thickness

    Photochem Photobiol

    (2005)
  • Bouillon R, Eisman J, Garabedian M, Holick M, Kleinschmidt J, Suda T, et al for the Standardized Action Spectrum for...
  • T.B. Fitzpatrick

    The validity and practicality of sun-reactive skin types I through VI

    Arch Dermatol

    (1988)
  • M.F. Holick

    Vitamin D: the underappreciated D-lightful hormone that is important for skeletal and cellular health

    Curr Opin Endocrinol Diabetes

    (2002)
  • Cited by (96)

    • Determinants of vitamin D levels from sun exposure

      2023, Feldman and Pike's Vitamin D: Volume Two: Disease and Therapeutics
    • Vitamin D and cardiovascular health

      2021, Clinical Nutrition
      Citation Excerpt :

      As there are very few natural sources of vitamin D in food, diet does not provide adequate amounts of vitamin D for most people [4,5]. Hence, in many situations in which sunlight exposure is inadequate, supplementation with vitamin D may be necessary [3,4,6,7]. An example of this situation is the confinement of people during the current coronavirus disease 2019 (COVID-19) pandemic.

    View all citing articles on Scopus

    Funding sources: None.

    Conflicts of interest: None declared.

    These two authors have equal responsibility for the work described herein.

    View full text