Although too much sunlight is associated with painful sunburns (erythema) and skin cancer, it is also paramount in producing Vitamin D in the body. Vitamin D exists in two major forms, Vitamin D3 and Vitamin D2, and is not typically found in foods. Sunlight, particularly UVB radiation, is essential for skin to synthesize Vitamin D from cholesterol by converting the biologically inactive form to the active form. Without Vitamin D, people are more susceptible to various diseases, such as rickets and osteomalacia.
Scientists at Polytechnic University of Valencia’s (UPV), located in Spain, studied the recommended minimum amount time humans need to be under the sunlight to get the necessary amount of Vitamin D. The research took place over four months in each season of the year for seven years beginning in 2003. The amount of time taken to get erythema and the recommended daily amount of Vitamin D was recorded.
In July, it took more than 29 minutes for someone of skin type III (a common type in Spain) to get erythema. Whereas in January, an individual can withstand the sun for more than 150 minutes. With 25% of the body exposed, it takes around 10 minutes for someone to gain the necessary vitamins. The winter time has much less solar radiation making it more difficult to attain a sufficient amount of vitamins. With 10% of the body exposed and at peak sunlight, it takes two hours to achieve the recommended dose. Later in the day, it takes almost even ten hours to obtain an optimal dose.
María Antonia Serrano, the main author of the study, said, “these calculations were made for skin type III, but the figures would change for those who are lighter or darker in complexion. It is also essential to bear in mind that we have considered the usual percentage of the body exposed for the season. If more skin is exposed, exposure time can be reduced.”
Like skin type, age is an important factor in how much the body synthesizes Vitamin D. The amount of Vitamin D produced from solar radiation decreases as one gets older. Middle aged adults only have 66% of the vitamin D that children produce. The amount of radiation the body absorbs also depends on what body parts are exposed since not all areas in the body produce Vitamin D at an equal rate.
Serrano concludes that, “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.” With this information future studies on the benefits of moderate sunbathing can be linked to supplementing Vitamin D deficiency.
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, 2017; 574: 744