Summer is here and many people can’t wait to start “taking vitamin D”, which is more popular than ever, even though it’s not really a vitamin or even a single substance. , but rather from a hormonal system that we absorb from the Sun. Research and public interest in vitamin D deficiency have grown over the past 10 years. “They [health care providers] asking for blood tests for vitamin D levels for no reason. When they learn that a patient has low levels of vitamin D, they prescribe treatment and even more blood tests,” said Ricardo González, family doctor and director of the San Fermín health center in Madrid. “A lot of people call it the ‘sunshine vitamin’ and want to check vitamin D levels as part of other routine blood tests. But few people want to take vitamin supplements when their levels are low. Vitamin D level tests should only be done for people with risk factors, and they should only take supplements if necessary,” he said.
August 1, 2022 will mark 100 years since biochemists Elmer McCollum and Marguerite Davis published a study in the Journal of Biological Chemistry who reported their discovery of vitamins A and B, and another substance “that helps build calcium”. They would ultimately give this new substance a name – vitamin D – a misnomer since vitamins are defined as essential compounds that our bodies cannot synthesize. However, the skin photochemically produces vitamin D when ultraviolet B (UV-B) rays irradiate a precursor of cholesterol in our body.
This system is now known to be essential for bone health and calcium and phosphate metabolism. Vitamin D deficiency is a worldwide health problem mainly caused by insufficient exposure to the sun, which provides more than 90% of the vitamin D that our body needs. This deficiency is estimated to affect over a billion people, especially the elderly, and some are calling it a pandemic. The remaining 10% of the vitamin D that our body needs is obtained by consuming fatty fish such as tuna, salmon or mackerel and, to a lesser extent, eggs and mushrooms. Recently, genetically modified tomatoes have been engineered to increase their vitamin D content.
“If we had lived centuries ago, we would all have adequate levels of vitamin D. But since we are no longer daytime creatures, and because we wear clothes and don’t do much outdoor exercise, it’s almost impossible to get all the vitamin D we have. need the sun. We have to get it through our diet,” said Esteban Jódar, an endocrinologist at Quirónsalud University Hospital in Madrid and professor at European University. To get enough sun without risking premature skin aging or melanoma, Jódar recommends “15 minutes of outdoor exercise in the morning and 15 in the afternoon with bare arms and legs.” However, in Spain and other countries north of the 35th parallel, the amount of UV-B radiation synthesized by the skin decreases in winter and spring. The diet can compensate for this deficiency if staple foods such as bread, milk and dairy products are fortified with vitamin D as they are in Nordic countries. But in other countries where these foods are not fortified, “we see a paradox that, despite having more sun, [vitamin D] the levels are lower than in the Nordic countries,” Jódar said.
When Carmen Madrigal, a pediatrician at the Doctor Morante health center in Santander (Spain), checks vitamin D levels in children, she says, “they are usually fair. But if they live in apartments and cities, they will have little sunlight, especially in winter, since many of their extracurricular activities take place indoors. Unlike some of her colleagues, she doesn’t recommend giving up sunscreen for children because “it doesn’t seem very smart. But it’s hard to know for sure if you’re doing the right thing,” she said.
As with many aspects of biomedicine, there are few certainties about vitamin D, some areas of consensus, and much debate among experts. José Manuel Quesada, a retired endocrinologist and researcher at the Maimónides Biomedical Research Institute in Cordoba (Spain), has dedicated his life to this area of study. “What do we mean when we say vitamin D?” he asks, rhetorically. He says this ambiguous term encompasses several compounds that form the vitamin D endocrine system, similar to that of other steroid hormones. A compound consists of two nutrients – cholecalciferol or vitamin D3. This is what our skin synthesizes from UV-B, and what we also get from certain foods. The other is ergocalciferol or vitamin D2, which is found in certain plants, yeasts and fungi. These produce a prohormone called calcifediol (25 hydroxyvitamin D3) – the compound measured by blood tests – and calcitriol or active hormone, the final link in the system.
Although there are still some disagreements, experts have established a normal range for calcifediol levels: between 30 and 70 ng/ml. Levels below 20 ng/ml indicate deficiency and levels below 10 ng/ml indicate deficiency. Jódar, who is a member of the mineral and bone metabolism group of the Spanish Society of Endocrinology and Nutrition (Sociedad Española de Endocrinología y Nutrición – SEEN), says the supplements should only be taken by people with lower levels. at 30 ng/ml and who have risk factors, such as elderly institutionalized patients, pregnant and lactating women and people suffering from obesity, diabetes, osteoporosis and other chronic diseases. Healthy people should only take supplements if they have levels below 20 ng/ml. In studies mainly conducted in wealthy countries, 88% of the population has some level of vitamin D insufficiency and almost 7% has a severe deficiency. SEEN found that in Spain, 80% of adults under 65, 100% of adults over 65 and 40% of minors have vitamin D levels below 20 ng/ml.
Although minor deficiencies do not produce symptoms, lack of vitamin D is associated with multiple pathologies, such as autoimmune disorders, infectious and cardiovascular diseases, and diabetes. It can lead to osteoporosis and, in extreme cases, produce severe softening of the bones called rickets in children and osteomalacia in adults, two rare phenomena in Spain. If so many people suffer from vitamin D deficiencies, why has this not led to epidemics of these diseases? From the point of view of primary care, Ricardo González affirms that “the deficit indicated by the analytical data does not correspond to the clinical picture”. Madrigal agrees. “We don’t see rickets anymore, which was common when my father was alive,” the retired pediatrician said. In 2016, the New England Journal of Medicine (NEJM) published a study titled “Vitamin D Deficiency: Is There Really a Pandemic?” in which several American specialists have argued that setting the minimum normal level of vitamin D at 20 ng/ml encompasses many healthy people. The study also concluded that too many drug tests are being done and supplements are being prescribed unnecessarily. The study authors believe that a more appropriate minimum normal level would be 12.5 ng/ml, which would encompass less than 6% of their compatriots.
SEEN does not recommend dosing calcifediol in people without risk factors, nor does it advocate routine supplementation with pharmacological preparations in adults under 50 to improve bone health. There is no evidence to support the use of supplements to achieve benefits when other medical conditions are present. “There are very few high-quality studies of cases in which the administration of vitamin D has been successful in alleviating a condition. Most of the studies that do exist have been poorly designed,” Jódar said. over the past 100 years have been poorly designed,” confirms Quesada. He claims that vitamin D has been studied as if it were a drug, not a nutrient, and that the trials are done with people who have normal levels of vitamin D, so administering more vitamin D will not improve anything.
Research on vitamin supplementation has yielded mixed results. In 1980, a study published in the International Journal of Epidemiology suggested that vitamin D supplements may protect against colon cancer after finding that mortality was higher in places with less natural light, such as large cities and rural areas at high latitudes. Another study recently published in Nutrientsspeculated that “numerous experimental studies in cultured cells and animal models have described a wide range of anti-cancer effects”, but added the caveat that “clinical trials have provided limited support for this hypothesis”.
A 2019 study published in the NEJM concluded that the supplements did not decrease the incidence of invasive cancers or cardiovascular events. Other research published in The BMJ medical professional journal found a protective effect against acute respiratory infections, especially in people with significant [vitamin D] deficits. Quesada studied its effect on coronavirus infections and concluded that low levels of calcifediol are associated with increased risk of COVID-19 infection, severity and mortality. But the National Institutes of Health (NIH) in the United States and the National Institute for Health and Care Excellence (NICE) in the United Kingdom say that taking vitamin D alone to prevent or treat COVID-19 is not justified. . However, a recent systematic review in the Journal of Clinical Endocrinology and Metabolism determined that vitamin D supplements reduce the risk of hip fracture, although “high-risk individuals, such as the elderly, institutionalized patients, and people with low vitamin D levels, may benefit the most.” more”.
Given all the uncertainties and conflicting research, Quesada believes we should follow the Nordic example and supplement staple foods with vitamin D for the general population, the same way iodine is added. with salt to help the proper functioning of the thyroid. “While all of this research is ongoing to determine if having good levels of calcifediol prevents cancer, cardiovascular disease or falls, let’s get the general population to adequate levels of vitamin D,” said said Quesada.
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