on June 30, 2026
Vitamin D is one of the most studied micronutrients of recent decades and continues to be an area of great interest in biomedical research. Traditionally considered an essential vitamin for bone metabolism, today it is recognized as a prohormone involved in multiple physiological functions through the activation of the vitamin D receptor (Vitamin D Receptor, VDR), expressed in numerous tissues of the body.
The classic function of vitamin D consists in maintaining the balance between calcium and phosphorus, an indispensable condition for bone mineralization, neuromuscular function, and the physiological renewal of skeletal tissue. However, the discovery of VDR expression in immune, cardiovascular, pancreatic cells, and other tissues has expanded scientific interest in possible extra-skeletal roles.
From a physiological point of view, vitamin D derives from two main sources.
The first is cutaneous synthesis, which occurs thanks to exposure to ultraviolet B (UVB) rays, through the photochemical conversion of precursors present in the skin.
The second is dietary intake and, when necessary, supplementation.
Historically, it was believed that cutaneous production represented the main source of vitamin D; today, lifestyle changes, reduced time spent outdoors, aging, and sun protection have profoundly altered this balance.
Numerous nutritional studies have shown that the average daily intake of vitamin D through diet alone is frequently lower than levels considered adequate.
In the elderly population, the risk of deficiency increases further due to reduced cutaneous synthesis efficiency and reduced light exposure.
According to Italian LARN, the vitamin D requirement in the adult population is 15 μg/day, while after age 75 it increases to 20 μg/day.
From a biochemical point of view, there are two main forms.
Vitamin D3 (cholecalciferol), derived from sterol precursors present in living organisms.
Vitamin D2 (ergocalciferol), obtained from ergosterol found mainly in yeasts and plant sources.
Both require a double metabolic activation, hepatic and renal, to transform into the biologically active form 1,25-dihydroxyvitamin D.
Commercial vitamin D3: a often little-known aspect
When consumers purchase a supplement containing vitamin D3, the origin of the raw material is rarely considered.
Historically, a large part of the vitamin D3 used in supplements is obtained from lanolin, a substance derived from sheep's wool.
From a molecular point of view, the final cholecalciferol is equivalent regardless of the production source, but the origin of the raw material may be relevant for dietary, ethical, or transparency choices.
In many commercial products, the source of cholecalciferol is not immediately highlighted on the label, and consumers may not be able to identify whether vitamin D3 comes from an animal source or another supply chain.
For those following a strictly plant-based diet, this aspect becomes particularly important.
Vitamin D3 from lichen: the vegan source of cholecalciferol
In recent years, a production supply chain has been developed that allows vitamin D3 to be obtained from lichens.
This is now the main source of vitamin D3 compatible with a vegan choice.
In popular language, it is often referred to as vitamin D obtained from “Icelandic lichen”.
From a metabolic point of view, cholecalciferol obtained from lichen is equivalent to vitamin D3 obtained from other sources and follows the same biological mechanisms after absorption and activation.
For consumers interested in a vegan choice, the truly useful criterion remains the declaration of lichen origin and the presence of any supply chain certifications.
New horizons of research: beyond bone metabolism
The discovery of the VDR receptor in numerous districts of the body has led to the development of observational and mechanistic studies that have explored the possible role of vitamin status in various clinical areas.
It is important to emphasize that the presence of epidemiological associations does not automatically equate to a causal or therapeutic effect of supplementation.
Vitamin D and the immune system
One of the most consolidated fields concerns immune function.
The active form of vitamin D modulates the activity of dendritic cells, T and B lymphocytes, and participates in the regulation of the immune response.
Biological effects have been identified that include:
regulation of the inflammatory response;
modulation of the function of antigen-presenting cells;
participation in the mechanisms of innate immunity;
stimulation of antimicrobial peptide synthesis.
For this evidence, EFSA has authorized the claim that vitamin D contributes to the normal function of the immune system.
Vitamin D and cardiovascular health
Among the most studied areas is the cardiovascular one.
Numerous observational studies have shown that low levels of 25-hydroxyvitamin D are associated with a less favorable cardiovascular profile and a higher frequency of cardiovascular events.
Several biological hypotheses have been proposed:
involvement in the regulation of the renin-angiotensin system;
effects on endothelial function;
modulation of inflammatory processes;
interactions with vascular metabolism.
These observations have led to the conduct of randomized clinical trials to evaluate the effects of supplementation.
The available results are, however, heterogeneous.
Large clinical studies and systematic reviews have not consistently shown that vitamin D supplementation reduces cardiovascular risk in the general population.
For this reason, current guidelines do not recommend the use of vitamin D to prevent cardiovascular events in the absence of specific nutritional indications.
Vitamin D and cancer research
The relationship between vitamin D and oncology also represents an area of great interest.
Experimental studies have shown that the VDR receptor is involved in processes that regulate:
cell proliferation;
differentiation;
apoptosis;
immune response.
Epidemiological studies have observed associations between vitamin status and the prevalence of certain oncological conditions.
However, the available evidence does not allow us to state that vitamin D supplementation prevents or treats neoplasms.
The main scientific societies recommend correcting any nutritional deficiencies without using vitamin D as a specific oncological strategy.
Towards a modern management of vitamin D
The evolution of research has transformed vitamin D from a simple regulator of mineral metabolism to a central element in the physiology of the organism.
However, it remains essential to distinguish between:
correction of documented deficiency;
maintenance of an adequate nutritional status;
use not supported by evidence for therapeutic purposes.
For the modern consumer, in addition to the quantity of vitamin D, the quality and transparency of the source used are also becoming increasingly important, with growing attention towards vitamin D3 formulations obtained from lichen as a vegan alternative.
Bibliography
Holick MF. Vitamin D deficiency. New England Journal of Medicine.
Cashman KD et al. Vitamin D deficiency in Europe.
Tripkovic L et al. Comparison of vitamin D2 and vitamin D3 supplementation. American Journal of Clinical Nutrition.
Pilz S et al. Vitamin D and cardiovascular disease.
Manson JE et al. Vitamin D supplements and prevention of cardiovascular disease.
Scragg R et al. Effect of monthly high-dose vitamin D supplementation.
Beveridge LA et al. Effect of vitamin D supplementation on blood pressure.
Giovannucci E et al. Vitamin D and cardiovascular risk.
Feldman D et al. Vitamin D and cancer.
EFSA Panel on Nutrition. Dietary Reference Values for Vitamin D.
