Summer is here and many people can’t wait to start “taking vitamin D”, more fashionable than ever, although it is not a vitamin or a single substance, but a hormonal system that we interact with the sun nourish. During the last decade, research and societal interest in its deficit have multiplied. “They ask for their blood counts without justification, and because many patients have low levels, the treatment and asking for the test are becoming increasingly popular,” says Ricardo González, general practitioner and director of the San Fermin Health Center, in Madrid. “Many know it as ‘the sunshine vitamin,’ and ask about its content in tests conducted for other reasons,” he adds. “But then fewer people want to take supplements when they’re down. It should only be requested in people with risk factors to replace them when they are low, ”concludes this specialist.
On August 1st, it will be a century since the American biochemist Elmer McCollum, co-discoverer with biochemist Marguerite Davis of vitamins A and B, described another “that promotes calcium storage”. Journal of Biological Chemistry and which would end up being dubiously called vitamin D: vitamins are defined as essential compounds that we cannot synthesize, but our skin produces these through exposure to ultraviolet B rays on a cholesterol precursor.
Today we know that this system is essential for bone health and calcium and phosphate metabolism. Its deficiency is a global health problem, mainly caused by insufficient sun exposure – from which we get the necessary 90% – which is estimated to affect more than a billion people, especially the elderly. In fact, it’s called a pandemic. The remaining 10% is provided by blue fish such as tuna, salmon or mackerel and to a lesser extent by eggs or mushrooms. Recent research has managed to increase the amount of transgenic tomatoes.
“With the lives we lived centuries ago, we would have adequate amounts, but since we’re not out during the day, are clothed, and don’t exercise outdoors, it’s almost impossible with diet to meet the requirements,” says Esteban Jódar, Endocrinologist at Quirónsalud Madrid University Hospital and Professor at European University. To get enough sun without increasing your risk of premature skin aging or sun-induced melanoma, Jódar recommends “15 minutes of exercise in the morning and 15 minutes in the afternoon with bare arms and legs.” However, in Spain, which is above the 35th parallel, skin synthesis is reduced in winter and spring as UV radiation decreases. Diet could compensate for this if staple foods such as bread, milk and their derivatives were fortified, as is the case in the Nordic countries. Since this is not the case, “there is a paradox that our values are lower than theirs despite more sun,” Jódar points out.
When Carmen Madrigal, a neighborhood pediatrician at Doctor Morante Health Center in Santander, asks about vitamin D levels in children, “they’re usually fine.” “If they live in apartments in city centers, they will hardly sunbathe, especially in winter, because many also do extracurricular activities indoors,” he adds. He doesn’t consider, like some of his colleagues, advising children not to put sunscreen on for the first 15 or 20 minutes of sun exposure because “it doesn’t seem like the most sensible thing to do.” “It’s a subject I have a hard time knowing if you’re doing well or not,” he concludes.
As is usual in biomedicine, about what we call vitamin D there is a handful of certainties, some consensus, and many areas of debate among the experts themselves. José Manuel Quesada, retired endocrinologist and researcher at the Maimonides Institute for Biomedical Research of Cordoba (IMIBIC), dedicated his life to this field. “What do we mean when we say vitamin D?” he asks. As the honorary professor at the University of Cordoba explains, this ambiguous name includes several compounds that make up the endocrine system of vitamin D, similar to that of other steroid hormones: First, two nutrients, cholecalciferol or vitamin D3 – which our skin synthesizes with the sun or is in present in the foods of animal origin mentioned above – and ergocalciferol, or D2, found in plants, yeasts and fungi. From them come the prohormone called calcifediol (25 hydroxyvitamin D3) – the compound measured by analytics – and calcitriol or active hormone, the final link in the system.
The levels that we consider normal for Calcifediol are set by consensus among experts. Although there are discrepancies, the general consensus is that blood levels should be maintained between 30 and 70 ng/mL. Values below 20 ng/ml indicate an insufficiency and below 10 ng/ml a deficiency. Dietary supplements should only be taken by people with risk factors (including institutionalized elderly, pregnancy and lactation, obesity, diabetes, osteoporosis) and below 30 ng/ml, or below 20 ng/ml in a healthy population, explains Jódar, which is part of the Mineral and Bone Metabolism Group of the Spanish Society of Endocrinology and Nutrition (SEEN). in the Studies conducted mainly in rich countries88% of the population is deficient and up to 7% are seriously deficient. Corresponding Recommendations for the general public According to SEEN, in Spain 80% and 100% of people over 65 and 40% of younger people have a value below 20 ng/ml.
Although a mild deficiency does not produce any symptoms, vitamin D deficiency is linked to several pathologies such as autoimmune diseases, infectious diseases, cardiovascular diseases or diabetes. In the bones, it favors osteoporosis and, in extreme cases, leads to a severe softening known as rickets in children and osteomalacia in adults, both exceptional in Spain. Why isn’t there an epidemic of these diseases when so many of us are vitamin D deficient? Of primary care, González considers that “the analytical deficit does not correspond to the clinic,” agrees with Madrigal. “You don’t see rickets anymore, it was there in my father’s time,” he emphasizes, also a pediatrician and already retired. In a review titled “Vitamin D Deficiency: Is There Really a Pandemic?” published in 2016 NEJM, several US specialists criticized that setting the minimum normal value at 20 ng/ml includes many healthy people. Also that there are too many check-ups and that unnecessary dietary supplements are administered. According to the authors, a reasonable cut-off would be 12.5 ng/mL, a level that would encompass less than 6% of their compatriots.
In any case, SEEN does not recommend measuring calcifediol in individuals without risk factors, nor does it recommend systematic supplementation with pharmacological preparations in adults under the age of 50 to improve bone health. There is also no evidence of using supplements to gain benefits against other pathologies. “There are very few high-quality studies administering vitamin D and correcting these diseases, most are poorly designed,” says Jódar. Quesada agrees, “All the trials that have been done over these hundred years are poorly designed.” As he explains, vitamin D is being studied as if it were a drug, not a nutrient, and the studies are being conducted in people with normal levels , where adding more can’t improve anything.
In fact, research on vitamin supplements provides mixed results. In 1980 a publication of the International Journal of Epidemiology suggested they could protect themselves from colon cancer after finding that their mortality was higher in places with less natural light, such as large cities and rural areas at high latitudes. According to a recent review in nutrient, “many experimental studies in cultured cells and animal models have described a wide range of anticancer effects”, although “clinical studies have provided only limited support for this hypothesis”. For example one of them published in NEJM, concluded in 2019 that dietary supplements do not reduce the incidence of invasive cancer or cardiovascular events. Other research published in The BMJ found a protective effect against acute respiratory infections, but especially in those with significant deficits. Quesada has studied its effect on coronavirus infections and has defended that low levels of calcifediol are associated with higher risk of infection, severity and mortality from Covid-19, but institutions like the National Institutes of Health (NIH) Americans or the PRETTY Britons say taking vitamin D alone to prevent or treat this infection is unjustified. A recent systematic review of The Journal of Clinical Endocrinology and Metabolism concluded that they reduce the risk of hip fractures, although “individuals at high risk, such as the elderly, those living in nursing homes, or those with low vitamin D levels may benefit the most.” In the face of uncertainty, Quesada insists on following the Nordic example of supplementing staple foods for the entire population with vitamin D, like adding iodine to salt to help the thyroid make its hormones: “As you go demonstrating if A good calcifediol level prevent cancer, cardiovascular disease or falls, we bring our population to reasonable numbers”.