{"id":152392,"date":"2026-05-27T12:37:50","date_gmt":"2026-05-27T10:37:50","guid":{"rendered":"https:\/\/encanto.it\/uncategorized\/vitamin-d\/"},"modified":"2026-06-01T17:02:25","modified_gmt":"2026-06-01T15:02:25","slug":"vitamin-d","status":"publish","type":"post","link":"https:\/\/encanto.it\/en\/food-supplements\/vitamins\/vitamin-d\/","title":{"rendered":"Vitamin D"},"content":{"rendered":"

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Vitamin D<\/h1>\n

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Vitamin D is technically a secosteroid \u2014 a steroid-like molecule with an open-loop structure \u2014 rather than a vitamin in the classical sense of the term. Unlike other vitamins, which must be introduced exclusively through the diet, Vitamin D can be synthesized by the body as a result of skin exposure to ultraviolet B (UVB) radiation from the sun. This unique feature makes it a case apart in the landscape of micronutrients: it is at once a vitamin, a hormone, and a skin photoproduct. <\/h2>\n

The two main forms of Vitamin D are Vitamin D2 (ergocalciferol)<\/strong> -of plant and fungal origin \u2014 and Vitamin D3 (cholecalciferol)<\/strong> \u2014 of animal origin, also produced by human skin exposed to the sun. Both are absorbed in the small intestine and undergo a two-stage activation process: first in the liver, where they are converted to 25-hydroxyvitamin D (calcifediol), the depot form measured in blood tests; then in the kidneys, where calcifediol is converted to calcitriol (1,25-dihydroxycholecalciferol) \u2014 the biologically active form that acts as a full-fledged hormone. <\/h2>\n

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Shortage: a public health problem<\/h2>\n

Vitamin D deficiency is among the most prevalent in populations in industrialized countries. In Italy, it is estimated that more than 70% of the population has insufficient levels of 25-hydroxyvitamin D in the blood-with peaks during the winter months and in segments of the population that spend little time outdoors. The threshold for insufficiency is generally set between 20 and 30 ng\/mL (50\u201375 nmol\/L), while severe deficiency is defined as below 10\u201312 ng\/mL. <\/p>\n

The main causes of deficiency are poor sun exposure \u2014 exacerbated by extensive use of sunscreen, opaque clothing, and a predominantly indoor lifestyle \u2014 and insufficient dietary intake. Athletes who train mainly indoors, the elderly, people with dark complexions, pregnant and lactating women, and those on vegetarian or vegan diets are the highest risk groups. <\/p>\n

Mechanism of action and main functions<\/h2>\n

Il calcitriolo \u2014 the active form of Vitamin D \u2014 acts as a steroid hormone: it binds to specific nuclear receptors (VDR, Vitamin D Receptor) found in almost every tissue in the body, regulating the expression of hundreds of genes. This explains why the documented functions of Vitamin D extend far beyond bone metabolism: <\/p>\n

    \n
  • Metabolismo del Calcio e del Fosforo<\/strong> \u2014 Vitamin D increases intestinal absorption of calcium (up to 30\u201340% under conditions of adequate availability, versus 10\u201315% under deficiency) and phosphorus. It regulates blood levels of calcium along with parathormone and calcitonin. <\/li>\n
  • Bone Health<\/strong> \u2014 the regulation of calcium metabolism, it is essential for bone mineralization. Severe deficiency causes rickets in children and osteomalacia in adults. Chronic deficiency contributes to osteoporosis. <\/li>\n
  • Muscle Function<\/strong> \u2014 VDR are present in skeletal muscle. Adequate levels of Vitamin D support muscle strength and neuromuscular coordination. Deficiency is associated with muscle weakness, myalgias, and increased risk of falls in the elderly. <\/li>\n
  • Immune System<\/strong> \u2014 Vitamine D modulates both innate and adaptive immunity. It stimulates the production of antimicrobial peptides (cathelicidin, defensins), regulates the inflammatory response, and influences T lymphocyte differentiation. Research has documented associations between Vitamin D deficiency and increased susceptibility to respiratory infections. <\/li>\n
  • Cardiovascular Function<\/strong> \u2014 VDRs are present in cardiac and vascular cells. Observational evidence associates low Vitamin D levels with increased cardiovascular risk, although the causal relationship is still being researched. <\/li>\n
  • Mood Regulation and Cognitive Function<\/strong> \u2014 VDRs are present in the brain. Growing evidence links Vitamin D deficiency to an increased risk of depression and cognitive decline, particularly in elderly populations. <\/li>\n<\/ul>\n

    Food sources<\/h2>\n

    Dietary sources of Vitamin D are relatively limited compared to other micronutrients. The richest are fatty fish \u2014 salmon, mackerel, herring, sardines, tuna – cod liver and egg yolks. Mushrooms exposed to UV light are the main plant source of Vitamin D2. Milk, dairy products and some plant drinks are often fortified with Vitamin D in Northern European and North American countries, but in Italy supplementation is not mandatory. <\/p>\n

    Given the low food availability and reliance on skin synthesis-often insufficient in Italian latitudes during the months of October through April \u2014 supplementation is recognized as a useful tool for maintaining adequate levels in the general population.<\/p>\n

    Vitamin D3 and D2: which one to choose in formulation<\/h2>\n

    Vitamin D3 (cholecalciferol) is generally considered the preferred form for supplement formulation, for two main reasons: it is the same form produced by human skin in response to the sun, and it is more effective than D2 in increasing and maintaining blood levels of 25-hydroxyvitamin D. Comparative studies indicate that D3 is about 1.7 times more potent than D2 in increasing serum levels at the same dose.<\/p>\n

    Vitamin D3 has traditionally been derived from sheep wool lanolin, making it unsuitable for vegan formulations. In recent years, a plant-derived Vitamin D3, extracted from Lichen Lichen usnea<\/em> or other lichen sources \u2014 with the same efficacy profile as animal D3 and compatible with plant-based and vegan formulations-has also become available. <\/p>\n

    Magnesium and Vitamin D: a necessary synergy<\/h2>\n

    Vitamin D does not act in isolation: its metabolism depends on enzymatic cofactors including Magnesium. The enzymes involved in the conversion of Vitamin D into its active forms \u2014 both in the liver and kidney \u2014 are Magnesium-dependent. Insufficient Magnesium intake may therefore limit the effectiveness of Vitamin D supplementation, even at adequate doses. In advanced formulations for bone and immune health, the combination of Vitamin D3 + Magnesium is considered more complete than Vitamin D alone. <\/p>\n

    Vitamin K2: Vitamin D’s partner for Bone and Cardiovascular Health<\/h2>\n

    Another relevant association in formulation is that between Vitamin D3 and Vitamin K2 (menaquinone, specifically MK-7). Vitamin D increases intestinal absorption of calcium, but it is Vitamin K2 that directs calcium to the bones and teeth-activating osteocalcin, a calcium \u2014 dependent bone protein-and away from soft tissue and vascular walls, where calcium deposition is undesirable. The D3+K2 combination is now considered synergistic for bone health and prevention of arterial calcification-two goals often pursued together in formulations geared toward longevity and cardiovascular health. <\/p>\n

    EFSA claims approved<\/h2>\n

    Vitamin D has an extensive list of health claims approved by EFSA under EC Regulation 1924\/2006:<\/p>\n

      \n
    • Vitamin D contributes to the normal absorption and utilization of calcium and phosphorus<\/em><\/li>\n
    • Vitamin D contributes to normal blood calcium levels<\/em><\/li>\n
    • Vitamin D contributes to the maintenance of normal bones<\/em><\/li>\n
    • Vitamin D contributes to the maintenance of normal teeth<\/em><\/li>\n
    • Vitamin D contributes to normal muscle function<\/em><\/li>\n
    • Vitamin D contributes to the normal function of the immune system<\/em><\/li>\n
    • Vitamin D contributes to the normal function of the immune system in children<\/em><\/li>\n
    • Vitamin D contributes to the normal process of cell division<\/em><\/li>\n
    • Vitamin D plays a role in the process of cell division<\/em><\/li>\n
    • Vitamin D contributes to fall risk reduction in the elderly<\/em> \u2014 disease risk reduction claim allowed only with specific indication for population over 60<\/li>\n<\/ul>\n

      The Italian regulatory framework: the AIFA Note 96 and the limitations of the Ministry of Health<\/h2>\n

      In Italy, Vitamin D has a dual regulatory perimeter that it is important to distinguish. As a drug<\/strong>, the prescription and reimbursability of cholecalciferol is regulated by AIFA Note 96<\/strong>, which defines the clinical conditions for which the prescription is charged to the SSN (osteoporosis, malabsorption, chronic renal failure, prolonged corticosteroid therapy, and other specific conditions). <\/p>\n

      As a dietary supplement<\/strong>, the Ministry of Health sets the maximum limit of Vitamin D at 2000 IU (50 \u00b5g) per day for adults.<\/strong> This is a conservative limit compared to the doses often recommended in clinical settings for deficiency correction (1600\u20144000 IU\/day), but it is the boundary within which supplements marketable without a prescription are placed. <\/p>\n

      \n

      Vitamin D is fat-soluble and accumulates in fat tissue: prolonged supplementation at excessive doses can cause hypervitaminosis D, with hypercalcemia and risk of calcification in soft tissue. Before supplementing with doses higher than those indicated on supplement labels, blood levels of 25-hydroxyvitamin D should be measured with a blood test and the dosage evaluated with your physician. <\/em><\/p>\n<\/blockquote>\n

      \n

      Always remember that it is important to consult a health care professional before starting any new supplement or treatment.<\/em><\/p>\n<\/blockquote>\n

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      Vitamin D regulates calcium, bone, immunity, and muscle. D3 vs D2, synergy with Magnesium and Vitamin K2, EFSA approved claims and Ministry of Health limits. <\/p>\n","protected":false},"author":18,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[167,164],"tags":[643,671,673,781,800],"class_list":["post-152392","post","type-post","status-publish","format-standard","hentry","category-vitamins","category-food-supplements","tag-sport-supplements","tag-functional-supplements","tag-nutraceuticals","tag-longevity","tag-vitamins"],"_links":{"self":[{"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/posts\/152392","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/users\/18"}],"replies":[{"embeddable":true,"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/comments?post=152392"}],"version-history":[{"count":5,"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/posts\/152392\/revisions"}],"predecessor-version":[{"id":152459,"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/posts\/152392\/revisions\/152459"}],"wp:attachment":[{"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/media?parent=152392"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/categories?post=152392"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/encanto.it\/en\/wp-json\/wp\/v2\/tags?post=152392"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}