For almost a century, it has been known that vitamin D is essential to maintain levels of phosphorus and calcium in the blood in the range necessary to have a healthy skeleton and muscles, and, in recent years, its relevance has been confirmed for the regulation of the immune system or brain development. For this reason, some epidemiological data are worrying, suggesting that up to 40% of the European population has a deficiency of this substance. This lack is more delicate in older people, especially menopausal women, because with age this vitamin is synthesized worse, pregnant women, obese people, because vitamin D is fat-soluble, and also in children.
The main route of vitamin D production is cholesterol in the skin, which generates it when exposed to ultraviolet radiation from the sun. Life changes, which keep us indoors for more and more time, may explain the lack of vitamin D, but some also blame the use of sunscreens that block solar radiation.
At this point a collision occurs between two opposing health effects. Skin cancers, although the majority are not lethal, are the most common among white-skinned people, something that makes the use of sun protection highly recommended, particularly in the hottest months in the middle of the day. Studies in Australia have shown that the application of sunscreens can reduce the incidence of skin cancer by between 10% and 15% and it is estimated that an increase in the use of these products by 5% in the population can reduce the incidence of melanoma by 10% in a decade.
The Spanish Photobiology Group of the Spanish Association of Dermatology published in 2020 some tables in which you can see the estimated margins of sun exposure, both in winter and summer, to obtain adequate stimulation of vitamin D production without burning depending on the type of skin. If you have skin type 3, the most common among Spaniards, in summer, eight minutes of exposure to your face or arms would be enough to reach adequate levels of vitamin D, and you would begin to suffer burns after 32 minutes. . In winter, the minimum dose of vitamin D would be 25 minutes and the burn would occur after an hour and a half of exposure. These figures would vary if you have lighter or darker skin and depending on the latitude, because being in Spain is not the same as being somewhere in the tropics. José Aguilera and María Victoria Gálvez, co-authors of the study, have developed the application UV Derma which helps to manage this information individually with your mobile.
Yolanda Gilaberte, head of the Dermatology Service at the Miguel Servet Hospital in Zaragoza and co-author of the document, recognizes the difficulty of achieving a balance between the necessary skin protection and the need for vitamin D. “There are scientific societies that recommend 20 nanograms per milliliter. of vitamin D, which is what guarantees musculoskeletal health, which prevents rickets or muscle problems,” explains Gilaberte. “But in recent years it has been seen that vitamin D has an important effect on our immune system, that when its levels drop we suffer more colds or the risk of cancer increases. Because of this immunoregulatory effect, there are societies that believe that levels should be above 30 nanograms,” she adds. “Achieving these levels in Spain in winter is very difficult, we would have to be exposed to the sun for a long time, and we also don’t know if vitamin D levels in winter or summer have to be the same,” says the dermatologist. “From twenty and below, it is clear that it is bad, but above there are doubts. It is a field in which there is still research to be done,” she summarizes.
In the balance between protection against excess sun and vitamin D deficiency, Gilaberte recalls a study they carried out on children in Huesca, in which they saw that those who put on factor 30 sun protection had better levels of vitamin D, probably because they were exposed to the sun for longer. Sunscreen does not completely block ultraviolet radiation, something that clothing does. If the skin of an unprotected person turns red after 20 minutes in the sun, with a factor of 2, 40 would be necessary and with a factor of 50, 1000 minutes (16.6 hours). “This is the theory, because we usually put on less than the amount used to calculate these factors in laboratories and the real factor on our skin is lower,” she concludes.
In a review of studies 2019, it was noted that, although there are experimental studies that suggest a theoretical risk of vitamin D deficiency from the use of sunscreen, there is no conclusive evidence that this occurs in real-life situations. This probably happens because people do not usually apply as much cream as in the experiments. In that work it was commented that more research is needed, especially with high factor sunscreens and in different ultraviolet radiation environments, but it was recalled that, in general, the benefits of these products in the prevention of skin cancer seem to outweigh the risk. of vitamin D deficiency.
Carmen Vidal, professor of nutrition at the University of Barcelona, agrees that, around vitamin D, there are still “quite a lot of uncertainties and a need for research.” “Lower levels than those established are detected, which may be due to less exposure to the sun, the use of more protection or a reduction in fat consumption, but we do not see that this is related to an increase in related diseases,” he explains. “This may be because the recommended levels are excessive or because of discrepancies in analysis methods,” she says.
As in the case of the use of sunscreen creams, the vitamin D that comes through the diet has also decreased due to measures with health benefits. “Fat consumption has been reduced, because obesity is a problem, and there were products, such as full-fat dairy products, that were a common source of vitamin D,” he summarizes. For the moment, it will be necessary to refine our knowledge of what healthy vitamin D levels are for each age, taking into account individual characteristics, and seek a balance between objectives that sometimes require contradictory measures.
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