90% of the vitamin D that we store in our body is synthesized through sun exposure. According to data from the Spanish Society of Family and Community Medicine (semFYC), in a country like Spain, which receives more than 2,500 hours of sunshine per year, it would be enough to expose the face and arms to the sun for between 5 and 15 minutes a day during the central hours of the day (and only between March and October) to maintain adequate levels. However, despite this starting point, a large part of the Spanish population lives with vitamin D deficiency and with levels of this vitamin much lower than those of citizens of other northern European countries that have much less hours of sunshine per year.
This has been confirmed by a study published in the journal Scientific Reports (Nature) and directed by Dr. Diana Diaz Rizzolo, PhD in Biochemistry, member of the August Pi i Sunyer Biomedical Research Institute (IDIBAPS) and professor at the Universitat Oberta de Catalunya (UOC). According to the results of the research, focused on Catalonia, 75% of the population would have low levels of vitamin D, a figure that rises to 80% in the case of the young population.
“The data could surprise us from the start given the solar exposure we have in Spain, but if we investigate a little more we will see that many countries in the Mediterranean basin such as Italy or Greece present the same deficits,” the researcher explained to EL PAIS by telephone, who considers that this general deficit has several explanations. On the one hand, there is low exposure to the sun during the hottest hours (“it is more difficult for us to go outside during those hours that would help us to save plenty of vitamin D for other times of the year when we don’t get as much sun”). On the other hand, sunscreens are being used more and more widely: “We know that their use is very beneficial for many things, but on the other hand, they prevent the synthesis of vitamin D.”
And finally, the diet, which although it is not the main source of absorption of vitamin D, also helps. “We do not eat enough portions of foods rich in vitamin D such as oily fish, and we do not usually bet on foods enriched with this vitamin such as milk. And, furthermore, we don’t have supplementation campaigns to make sure that the population has optimal levels, as they do in the Nordic countries ”, he reflects. In Sweden, for example, even in the northernmost regions, the percentage of people with vitamin D deficiency does not reach 20%.
Deficiencies in vitamin D supplementation and control are precisely two of the most significant data provided by the research led by Diaz Rizzolo. According to them, only 10% of the Spanish population have their vitamin D levels analyzed and, when they are analyzed, many times, despite being deficient, they do not supplement. “We are supplementing less than half of the population with vitamin D deficiency,” says the author, who nevertheless acknowledges that these data are in line with what the guidelines of the main scientific societies such as the European Society of Endocrinology dictate, that only recommend the analysis and supplementation in population groups considered at risk, including the elderly, people with malnutrition and with bone problems and fractures, patients with diseases that affect bone metabolism or citizens who have very low exposure solar.
“The curious thing is that, until recently, vitamin D was something that was almost never analyzed, except in recommended cases,” explains Violeta Ramirez, a primary care physician in the Balearic Islands and coordinator of the Nutrition and Food work group. of the semFYC. However, she adds, there is now a lot of interest in vitamin D, and levels are increasingly being asked for in primary care clinics. For example, in women who are seeking pregnancy without achieving it, or in people of 40 or 50 years of age who come to the consultation referring muscle and bone pain. “These cases are not among the assumptions to request the levels, but the curious thing is that every time you ask for them, you see that yes, that the results coincide with those of the study: the levels are suboptimal and, even, there are people who present a severe vitamin D deficiency”, explains the expert, who considers that more research is necessary to see if it is advisable to generalize the request for these analyzes: “In the end, in medicine, everything is money. I would say that it might be necessary to generalize these analyses, but then the managers will tell us that it is unsustainable to do them to everyone”.
Solid evidence on the role of vitamin D is lacking
For Violeta Ramirez, the greatest risk of vitamin D deficiency is associated with frailty in the elderly. “In this population group, the deficit increases the risk of bone fracture and, consequently, morbidity and mortality, since in these people a fracture can be the end.” Along the same lines, a recent study published in Annals of Internal Medicine by Australian researchers based on data from more than 300,000 patients from the UK Biobank concluded that vitamin D deficiency is associated with increased risk of mortality; and that the greater the deficit, the more the risk increases.
“Our study highlights the need to prevent vitamin D deficiency and suggests that the benefits of doing so are widespread, particularly in people with very low levels of this vitamin, who are also often the most vulnerable, such as elderly who live in a residence and can barely spend time outdoors, ”reflects Elina Hyppönen, lead author of the study and director of the Australian Center for Precision Health, by email.
For Diana Diaz Rizzolo, what is complicated in this type of study is proving a causal relationship between vitamin D deficiency and mortality. A handicap, the lack of robust scientific evidence, which for the researcher at the August Pi i Sunyer Biomedical Research Institute is what hinders the generalization of the analyzes and vitamin D supplementation. There is a lot of interest, but little conclusive data. Only in 2022, in fact, research was published that, for example, linked a vitamin D deficiency with chronic inflammation, with worse brain function and dementia (led by Elina Hyppönen herself), with a greater severity of the disease and higher mortality rates among hospitalized patients with covid 19, with the risk of losing muscle strength, with worse survival data in patients with melanoma and its supplementation with an improvement in symptoms in patients with depression.
However, there are also studies that point in the opposite direction. Without going any further, an investigation published in summer in The New England Journal of Medicine concluded that vitamin D supplementation, compared with placebo, did not reduce total, nonvertebral, or hip fractures in healthy older and middle-aged adults. And other investigations warn of the risks of excessive supplementation.
“The most important thing right now is to know exactly what role vitamin D has in different aspects of health, since up to now we have very basic scientific evidence that prevents clinical decisions that affect an entire population group from being made. We need more science”, concludes Diaz Rizzolo.
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Source: EL PAIS