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Researchers estimate duration of sun exposure necessary for vitamin D production in Spain

Posted on: March 14, 2017   by  Vitamin D Council


Researchers from the Solar Radiation Research Group at the Polytechnic University of Valencia (UPV) estimated the time needed to make 1,000 IU of vitamin D from the sun, and avoid sunburn among individuals from Spain.

Despite common misconception, vitamin D deficiency is still common in warm places, such as California, Spain or Pakistan. This study was conducted to determine the ease or difficulty of getting vitamin D throughout the year without risking unsafe sun exposure.

The researchers analyzed ultraviolet solar irradiance (UVER) during peak sun hours, usually between solar noon and 1:30, one month per season. All individuals in the study were considered to have skin type III, a common skin type in Spain. The researchers wanted to find out how long it takes to make 1,000 IU of vitamin D, as well as the time it would take for an individual to risk burning the skin.

The table below shows the different skin types:
Skin Type Skin color Skin characteristics


Type I

Very fair; red or blond hair; blue eyes; freckles Always burns, never tans


Type II

Fair; sandy or red hair; blue, hazel or green eyes Usually burns, tans with difficulty


Type III

Fair; with any eye or hair color; very common Sometimes mild burn, gradually tans


Type IV

Dark brown hair, green, hazel or brown eyes. Rarely burns, tans with ease


Type V

Dark brown and black hair; brown and dark brown eyes. Very rarely burns, tans very easily


Type VI

Black hair, dark brown eyes. May never burn, tans very easily

This is what the researchers found:

  • During the months of spring and summer, an individual can make 1,000 IU of vitamin D in 10 minutes, with only 25% of the body exposed, but must not spend more than 29 minutes outside, or risk sunburn.
  • During the month of January (winter), an individual can make 1,000 IU of vitamin D in 130 minutes, with 10% of the body exposed, but must not spend more than 150 minutes outside, or risk sunburn.
  • Researchers estimated that during the month of October (fall), about 30 minutes would be sufficient for the body to produce 1,000 IU of vitamin D.

The researchers acknowledged that the data for this study could be affected by factors such as, percentage of skin exposure, skin type, age and location in the world. This study only reviewed results pertaining to skin type III, and did not expand their research to regions outside of Spain. For areas farther away from the equator, and for skin types darker or lighter than type III, vitamin D absorption from the sun can change drastically.

María Antonia Serrano, scientist and main author of the study, concluded:

“These results can help to adopt the right measures to make up for any deficiency, such as informing the medical profession about the utility of increasing vitamin D intake in the diet or through supplements.”


Maria-Antonia Serrano ⁎, Javier Cañada †, Juan Carlos Moreno, Gonzalo Gurrea. Solar ultraviolet doses and vitamin D in a northern mid-latitude. Science of the Total Environment, 2016.

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