“GDear doctor, I did the tests and my vitamin D is 18 ng/mL. The doctor told me it’s ‘low normal’ and wasn’t worried. But I’ve read around that almost all of us are deficient in it and that you also need vitamin K2 and magnesium to really make it work. I got confused. Can you clarify?”
It depends on what is meant by “normal”, 18 ng/mL is below the threshold of 30 ng/mL that the main international scientific societies, including theEndocrine Society and the Italian Society of Orthopedics and Musculoskeletal Medicineindicate as a minimum target in menopausal and post-menopausal women and in those with metabolic or bone pathologies. Many doctors still refer to older thresholds, but the More recent guidelines are clear: below 30 ng/mL we speak of significant insufficiency. The value of 12 ng/mL, currently used by AIFA as the threshold for reimbursement of the supplement, does not represent an optimal clinical target: it represents the threshold below which the NHS covers the drug and thank goodness!
For women between the ages of 40 and 55, the most defensible target is between 40 and 60 ng/mL. Some studies (in particular those by Wimalawansa and Hollis, among the world’s leading experts on the subject), say that levels above 50 ng/mL are required for optimal immune system function. The 30 ng/mL, while sufficient for basic bone health, leaves most other systems uncovered.
The 50–70 ng/mL range is now supported by a significant part of the scientific literature.
A hormone, not just a vitamin
For decades, vitamin D has been reduced to an orthopedic topic. Calcium, bones, rickets. Then the research changed perspective, because Vitamin D receptors are found in almost all tissues of the body: immune system, heart, brain, muscles, intestine. Technically it is a hormone, produced by the skin and then circulates in the blood and acts remotely on many organs and systems, not just the bones.
In fact, evidence from recent years links it to much broader processes than just bone mineralization. It significantly modulates the immune response, both innate and adaptive, reducing susceptibility to infections and the tendency to chronic inflammation. Participates in mood regulation, maintenance of muscle strength, cardiovascular health. Some associations are still being confirmed with long-term studies, but the overall picture is already sufficient to justify serious clinical attention.
Because so many people lack it
In Italy the estimated prevalence of insufficiency or deficiency exceeds 70-80% of the population, with even higher peaks in women over 50. The figure is surprising in a Mediterranean country. The explanation is less trivial than it seems.
The sun only produces vitamin D when UVB rays reach the skin at a sufficient angle. In Italy, from October to April, this rarely happens: the sun’s rays are too inclined (above the 37th parallel, which cuts through Italy at the height of Sicily, the angle is not sufficient for months). In summer, those who use sunscreen, those who work indoors, and those who do not expose adequate body surface area produce very limited quantities. And two weeks at the beach in August are not enough to build reserves for the whole year.
Then there is a variable that is rarely considered: a significant portion of the population carries genetic variants of the vitamin D receptor (VDR) that reduce its efficiency. For these people, even with good sun exposure and standard supplementation, the levels struggle to rise satisfactorily, because the signal arrives attenuated from the beginning. Understanding this changes the strategy: often you simply need a higher dose than usual. This is a silent fragility, which is easily identified with a genetic test on a buccal swab.
Vitamin D is fat-soluble: it accumulates in adipose tissue, but is depleted within a few months. The diet contributes very little, covering a maximum of 10-20% of the requirement through fatty fish, egg yolk and a few other foods.
The role of magnesium: a point often ignored
Many people supplement with vitamin D for months without seeing levels rise. In several cases the reason is simple: magnesium is missing.
Magnesium is an indispensable cofactor for both reactions that transform vitamin D into its active form: first in the liver, then in the kidney. Without an adequate intake of magnesium, integrated vitamin D remains partly unused. The problem is that magnesium deficiency is also very widespread, especially in women with chronic stress. Serum magnesium values, the ones we normally see in blood tests, reflect only a small fraction of the body’s reserves, and can be normal even when the body is actually depleted. Normal magnesium in tests does not exclude a functional deficiency.
And vitamin K2?
When vitamin D increases intestinal absorption of calcium, that calcium must reach the bones and not be deposited in the arteries or soft tissues. This is the job of vitamin K2, specifically in the MK-7 form: activates proteins that guide calcium towards the skeleton and keep the arteries free from calcifications.
In the absence of K2, high doses of vitamin D can increase circulating calcium without it finding appropriate destinations, with a potential risk of vascular deposits. Those who supplement vitamin D in significant quantities and for prolonged periods have good reasons to always combine it with K2 in the right proportions.
Daily doses, not monthly boluses
The most recent international guidelines clearly indicate that daily administration is physiologically superior to the monthly or quarterly megadoses that have long been used as a practice. Bolus doses create blood spikes followed by rapid crashes and can paradoxically activate enzymes that degrade vitamin D. A consistent, modest dose each day keeps levels stable much more effectively. It’s the way the body expects to receive it.
On the risk of toxicity
Vitamin D toxicity circulates as a concern that is often disproportionate to the actual risk. Documented cases of hypervitaminosis with serious clinical consequences, hypercalcemia, renal damage, calcifications occur rarely and with blood levels higher than 150-200 ng/mL and in specialized literature cases without toxicity up to 200 ng/mL and above are reported (for the 25-OH-D3 form). The doses commonly used in clinics to correct a deficiency, from 1,000 to 2,000 IU per day, typically bring levels far from those thresholds. The tolerable upper limit set by the Endocrine Society for healthy adults is 4,000 IU per day.
Vitamin D is fat-soluble and accumulates, so periodic checking of levels remains a good habit. But the fear of overdose, often amplified by out-of-context information, should not become an obstacle to integration when it is indicated.
Knowing your starting value, reevaluating it every few months and calibrating the dose accordingly is the only truly intelligent way to proceed. Vitamin D is a hormone that the human body expected to receive from the sun, and which modern life has largely taken away from us.
Doctor Federica Almondo
Doctor Federica Almondo.
Specialist in Nutrition Science, trained at the Dietology and Obesity Center of the San Raffaele Hospital in Milan, Doctor Federica Almondo is a point of reference in personalized nutrition, preventive medicine and anti-aging pathways.
After founding and directing Cerva 16 – Nutrition & Anti-aging Center, he is now responsible for the Nutrition and Longevity areas of Image Regenerative Cliniccenter of excellence and international point of reference for Regenerative Medicine and Aesthetic Medicine with offices in Milan and St. Moritz.
It deals with tools such as genetic tests (DNA), assessments of the state of the intestinal microbiota, analysis of oxidative stress, body composition, indirect calorimetry, ANS Analysis to build highly personalized diets with a holistic and scientifically validated approach, suitable for even the most complex needs.
With excellent training and skills ranging from nutrigenetics and nutrigenomics to nutraceutics, metabolomics and epigeneticsAlmondo is also recognized for her work on intestinal health, menopause, chronic stress management and optimization of psycho-physical energy. Particular attention to ketogenic therapya nutritional approach now totally validated by scientific literature such as effective intervention in many complex pathologiesincluding type 2 diabetes, PCOS, fibromyalgia and lipedema and much more.