When we spend time sitting next to a window through which the sun’s rays enter, we can feel how they warm and illuminate. They can even burn our skin, as if we were lying outdoors,” explains Cristina Eguren, dermatologist at the clinic that bears his name, in Madrid, and member of the Spanish Academy of Dermatology and Venereology (AEDV). What we notice is the effect of type A ultraviolet rays (UVA), which are able to penetrate the glass and reach us. But is this enough to synthesize the vitamin D the body needs to absorb the calcium that protects the bones?
The answer is no. The radiation that helps this process, type B ultraviolet (UVB), is left out (there is a third, ultraviolet C, which is completely absorbed by ozone in the atmosphere). This can be a problem even in the “land of the sun”, where ironically vitamin D levels are similar to or lower than those described for central Europe or Scandinavia, according to a study in the Journal of Osteoporosis and Mineral Metabolism. I mean, low. “And its deficit decreases the absorption of calcium at the intestinal level and promotes the expense of the stored in the bone”, warns Francisco Vargas Negrín, of the working group in Rheumatological Diseases of the Spanish Society of Family and Community Medicine (semFYC).Its function may even go beyond maintaining bone health, as there are studies linking low vitamin D levels with autoimmune diseases and increased susceptibility to infections.
To avoid this, it is necessary to receive solar radiation in the open air, although without going over it: “20 minutes a day of exposure in shirt sleeves and shorts are enough for correct levels,” clarifies the dermatologist. And now, if the windows block the radiation that we use to synthesize the vitamin and we cannot go outside, where are we going to get it from? The most immediate answer is in the open windows and the balconies, but the circumstances encourage to be especially cautious with the diet , a humble source from which only 20% or less of all the vitamin D that the organism obtains comes from.
As Lourdes Carrillo, from the semFYC Nutrition Group, previously explained to this magazine, it is not a good idea to resort to food to obtain the necessary vitamin D: “A liter of milk provides 200 to 400 international units and the daily need is 600 to 800 units for a healthy adult, so you should drink almost two liters of milk a day. ” However, and given the circumstances, it is also worth knowing which foods have the highest content of this vitamin, which is mainly found in dairy products and their derivatives.
A serving of mackerel, for example, provides 90% of the daily needs for vitamin D. Tuna is also rich in this micronutrient, as are sardines, which when canned have the advantage that they can be eaten up to the bone, with the calcium it contains. An egg contains a fifth of the recommended daily intake, and shellfish such as shrimp, prawns, clams, and oysters also provide the vitamin. Among foods that are not of animal origin, mushrooms are one of the few foods rich in this nutrient.