on July 01, 2026
Skeletal health depends on the continuous interaction between nutritional, hormonal, metabolic, and mechanical factors. Among all the micronutrients involved in bone maintenance, calcium and vitamin D represent one of the most studied and best characterized biological systems. Their balance conditions the maintenance of bone mass, the quality of mineralization, muscle function, and the risk of skeletal fragility over the course of life.
In recent decades, osteoporosis has become one of the main chronic conditions associated with the aging population. In Europe, it affects tens of millions of people and represents one of the major causes of fragility fractures, loss of autonomy, and increased disability in old age.
Bone metabolism is regulated by an integrated system in which vitamin D, calcium, parathyroid hormone (PTH), calcitonin, kidney function, nutritional status, and physical activity intervene.
Vitamin D promotes the intestinal absorption of calcium and phosphorus and contributes to the maintenance of adequate plasma concentrations to allow normal bone remodeling processes. When vitamin D levels are insufficient, the body tends to compensate by increasing parathyroid hormone secretion, with a consequent increase in bone resorption.
This adaptation mechanism, defined as secondary hyperparathyroidism, over time can contribute to the reduction of bone mass and the increase of skeletal fragility.
Vitamin D is not a single compound but includes different biological forms.
The two main ones are:
Vitamin D3 (cholecalciferol)
Vitamin D2 (ergocalciferol)
Both must be activated through two metabolic steps, initially in the liver with the formation of 25-hydroxyvitamin D and subsequently in the kidney to obtain the biologically active form 1,25-dihydroxyvitamin D.
From a nutritional point of view, vitamin D3 generally represents the form most used in supplementation.
However, a little-discussed aspect concerns the origin of the raw material.
Most of the vitamin D3 present on the market is historically obtained from lanolin, a substance derived from sheep's wool. In other cases, the origin is not immediately made evident to the consumer.
For those who follow a vegan diet or desire greater transparency in the choice of raw materials, this represents an important element.
Currently, the main vegan alternative to vitamin D3 of animal origin is represented by vitamin D3 obtained from lichen.
In popular language, it is often referred to as vitamin D from Icelandic lichen.
This source allows obtaining cholecalciferol compatible with a plant-based diet while maintaining the same biological characteristics of vitamin D3 once absorbed.
In fact, after ingestion, the molecule follows the same metabolic pathways and participates in the same physiological processes as vitamin D, regardless of its origin.
Vitamin D and fracture risk: what the studies show
Fragility fractures represent one of the main clinical consequences of osteoporosis.
With advancing age, there is a decrease in:
the skin's ability to synthesize vitamin D;
intestinal calcium absorption;
osteoblastic activity;
the body's adaptive response.
These changes progressively contribute to the loss of bone mass.
Several clinical studies and meta-analyses have evaluated whether vitamin D and calcium supplementation can reduce the risk of fracture.
Analyses conducted on elderly populations at risk have observed that maintaining an adequate calcium intake associated with adequate vitamin D availability can contribute to the reduction of osteoporotic fractures, especially in subjects with documented nutritional deficiency.
The relationship between calcium and vitamin D is strictly physiological.
A high calcium intake with a vitamin D deficiency may not guarantee adequate absorption.
Conversely, vitamin D supplementation in the presence of a low calcium intake may not optimize mineral metabolism.
For this reason, the main guidelines consider the maintenance of an adequate vitamin status as an integral part of the prevention of bone fragility.
Bone as a metabolically active tissue
Bone does not represent a static structure.
It is an organ in continuous remodeling through the balance between:
osteoblasts, responsible for formation;
osteoclasts, responsible for resorption.
Vitamin D participates indirectly in the regulation of this balance through the control of calcium-phosphorus homeostasis.
Other micronutrients also perform important functions.
Magnesium: involved in the regulation of PTH secretion.
Vitamin K: involved in correct mineralization.
Vitamin C: essential for the synthesis of bone collagen.
Dietary proteins: necessary to maintain muscle structure and function.
For this reason, the maintenance of bone health cannot be reduced to supplementation alone but requires a global approach.
Sun exposure, diet, and supplementation
Cutaneous synthesis continues to represent an important physiological source of vitamin D.
Exposure to UVB rays remains a fundamental biological mechanism, even if efficiency decreases with age.
Diet contributes to a lesser extent.
The main traditional natural food sources are predominantly of animal origin.
For those who follow a vegan or plant-based diet, this makes the selection of formulations that clearly state vitamin D3 obtained from lichen particularly relevant.
When considering supplementation, it is appropriate to evaluate:
age;
sun exposure;
nutritional status;
any conditions that alter absorption or metabolism;
blood levels of 25(OH) vitamin D when clinically indicated.
Supplementation must be personalized and does not replace a clinical evaluation in individuals with osteoporosis, renal failure, mineral metabolism disorders, or other medical conditions.
Bibliography
Bischoff-Ferrari HA et al. Fracture prevention with vitamin D supplementation: meta-analysis.
Dawson-Hughes B et al. Effect of calcium and vitamin D supplementation on bone density.
Holick MF. Vitamin D deficiency. New England Journal of Medicine.
Bikle DD. Vitamin D: newly discovered actions require reconsideration of physiologic requirements.
Ahmadieh H, Arabi A. Vitamins and bone health: beyond calcium and vitamin D.
Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D.
SINU. LARN – Nutrient and Energy Reference Intake Levels for the Italian Population.
Cashman KD et al. Vitamin D deficiency in Europe.
Tripkovic L et al. Comparison of vitamin D2 and vitamin D3 supplementation.
EFSA Panel on Nutrition. Dietary reference values for vitamin D.
