on August 30, 2026
Vitamin D also contributes to the maintenance of normal muscle function.
The vitamin D receptor is present in various tissues throughout the body, and muscle function is one of the main areas of research interest.
A severe vitamin D deficiency may be associated with muscle weakness and alterations in neuromuscular function. This is particularly relevant in the elderly population, in whom loss of muscle mass, sarcopenia, and reduced balance may increase the risk of falls.
However, in this case too, modern research urges us to avoid simplistic interpretations.
Correcting a vitamin D deficiency is a clinically relevant goal, but the indiscriminate administration of vitamin D to people without a specific need has not proven to be a universally effective strategy for preventing falls and fractures.
A meta-analysis of randomized trials conducted on tens of thousands of older adults found no statistically significant reduction in falls or fractures with generalized vitamin D supplementation.
Fall prevention therefore requires a broader approach that includes physical activity, strength and balance exercises, adequate protein intake, vision assessment, medication review, and frailty prevention.
Vitamin D is one of the components of this system, not the sole determinant.
Vitamin D and the immune system
One of the most interesting areas of research concerns the relationship between vitamin D and the immune system.
The vitamin D receptor, or VDR, is expressed in various cells involved in the immune response. The active form of vitamin D can modulate the activity of innate and adaptive immune cells and influence the expression of molecules involved in the antimicrobial response.
Among the mechanisms studied is vitamin D's ability to promote the expression of certain antimicrobial peptides and modulate the activity of dendritic cells, T lymphocytes, and B lymphocytes.
These mechanisms explain why vitamin D is considered an important modulator of immune function.
From a regulatory standpoint, the claim that vitamin D contributes to the normal function of the immune system is authorized in the European Union.
However, vitamin D's biological role in the immune system does not mean that high doses of supplements can indiscriminately prevent all infections or indefinitely boost the body's defenses.
In this case too, it is necessary to distinguish between maintaining an adequate vitamin status and the pharmacological or indiscriminate use of high doses.
In the large DO-HEALTH study, conducted on 2,157 European adults aged 70 or older, daily supplementation with 2,000 IU of vitamin D3 did not result in a statistically significant improvement in the infection rate in the overall population studied.
Research therefore suggests that vitamin D plays an important physiological role in immune function, while the clinical effects of supplementation probably depend on the initial vitamin status, population characteristics, and the health outcome considered.
Vitamin D and aging
Interest in vitamin D increases with age.
Aging can reduce the skin's ability to synthesize vitamin D and, at the same time, increase the likelihood of conditions associated with reduced mobility, less sun exposure, or absorption alterations.
Vitamin D is also closely linked to musculoskeletal health, one of the fundamental elements for maintaining autonomy and quality of life during aging.
For this reason, assessing vitamin status may be particularly relevant in older adults, institutionalized individuals, in cases of reduced sun exposure, and in the presence of risk factors for bone fragility.
However, the most recent evidence does not support the idea that vitamin D administration in generally healthy and adequately supplied people is able, on its own, to globally slow aging.
In the DO-HEALTH trial, three years of vitamin D3 supplementation did not result in a statistically significant improvement in physical function, cognition, blood pressure, or the incidence of non-vertebral fractures in generally healthy older adults.
Vitamin D should therefore be considered an important component of healthy aging physiology, but not a single solution to the complex biological processes associated with age.
Vitamin D and dementia: what studies really say
Numerous observational studies have found an association between low circulating levels of vitamin D and an increased risk of cognitive decline, dementia, and Alzheimer's disease.
One of the most cited prospective studies observed an association between severe vitamin D deficiency and a higher risk of developing dementia and Alzheimer's disease.
These data are biologically interesting. The nervous system expresses the vitamin D receptor, and several potential mechanisms have been studied, including the modulation of inflammation, oxidative stress, calcium homeostasis, and certain neuroprotective processes.
However, it is essential to distinguish between epidemiological association and demonstration of causality.
People with low vitamin D levels may simultaneously have other factors associated with a higher risk of cognitive decline, such as reduced physical activity, frailty, less exposure to the outdoors, chronic diseases, or nutritional alterations.
For this reason, it is not scientifically correct to state that vitamin D deficiency directly “causes” Alzheimer's disease.
Available clinical studies have not yet conclusively demonstrated that vitamin D supplementation prevents dementia in the general population. In DO-HEALTH, vitamin D3 did not result in a significant improvement in cognitive function in the participants overall.
Maintaining an adequate vitamin status remains important for overall health, while the possible specific role of vitamin D in preventing neurodegenerative diseases continues to be a subject of research.
Vitamin D and cardiovascular health
For many years, epidemiological studies have shown an association between low vitamin D levels and an increased cardiovascular risk.
Several biological mechanisms have been proposed: modulation of the renin-angiotensin system, effects on glucose metabolism, regulation of inflammation, endothelial function, and calcium metabolism.
However, large clinical trials have downplayed the hypothesis that vitamin D supplementation can be used indiscriminately as a cardiovascular prevention strategy.
In the VITAL trial, conducted on over 25,000 adults, supplementation with 2,000 IU per day of vitamin D3 did not statistically significantly reduce the overall incidence of invasive cancers or major cardiovascular events compared to placebo.
The DO-HEALTH study also did not show a statistically significant benefit of vitamin D3 on blood pressure in the generally healthy older population.
The D-Health Trial observed a possible small reduction in some cardiovascular events with monthly administration of vitamin D3, but the overall effect on major cardiovascular events was limited in magnitude and the confidence intervals were also compatible with no effect.
Overall, the available evidence does not allow vitamin D to be used as a substitute for established cardiovascular prevention strategies.
Diet, physical activity, blood pressure control, smoking cessation, body weight management, and treatment of risk factors remain the main tools of prevention.
Vitamin D and cancer prevention
In oncology too, interest in vitamin D initially derives from epidemiological observations and experimental studies.
The vitamin D receptor is present in numerous tissues and cellular studies have shown that vitamin D can influence cell proliferation, differentiation, and some immune regulation mechanisms.
These data have led to the hypothesis of a possible role of vitamin D in the prevention of some neoplasms.
However, the biological hypothesis does not automatically coincide with a demonstrated clinical benefit.
In the large VITAL trial, daily supplementation with 2,000 IU of vitamin D3 did not significantly reduce the overall incidence of invasive cancers compared to placebo.
Therefore, at the current state of knowledge, it is not correct to present vitamin D as a supplement capable of preventing cancer in the general population.
Research remains active, however, especially to understand whether specific subgroups characterized by vitamin deficiency or particular biological conditions may obtain different benefits.
Vitamin D, body weight, and metabolism
Vitamin D is often associated with body weight control, especially because low concentrations of 25(OH)D are frequently observed in overweight and obese people.
This association may depend on multiple factors, including the different distribution of vitamin D in adipose tissue and the complex relationships between obesity, metabolism, diet, and physical activity.
The presence of low levels of vitamin D does not, however, prove that vitamin D is a slimming treatment.
There is insufficient evidence to state that vitamin D supplementation alone produces a significant reduction in body weight in the general population.
Correcting a possible deficiency may be important for health, but it should not be confused with a direct treatment of obesity.
How to assess vitamin D status
The main test used to assess the body's reserves is the blood concentration of 25-hydroxyvitamin D [25(OH)D].
The interpretation of the result requires attention because different guidelines and scientific societies may use thresholds that are not completely overlapping.
For this reason, it is preferable to avoid interpreting a single value independently without considering age, clinical conditions, the presence of osteoporosis, renal function, intestinal diseases, medications, and other risk factors.
Particular attention may be necessary in people with:
reduced sun exposure;
advanced age;
osteoporosis or increased risk of fractures;
gastrointestinal diseases associated with malabsorption;
obesity;
liver or kidney diseases;
use of certain medications that interfere with vitamin D metabolism.
The vitamin D concentration must also be interpreted in the context of overall mineral metabolism. In certain clinical situations, the assessment of serum calcium, parathyroid hormone, renal function, and other parameters may also be useful.
Supplementation must be personalized
Vitamin D is a fat-soluble vitamin and can accumulate in the body.
This means that supplementation should not be considered without limits. Excessive doses, especially if taken for prolonged periods, can cause hypercalcemia and other complications.
For this reason, it is not correct to automatically assume high doses just because vitamin D is considered beneficial.
The appropriate amount depends on several factors:
age;
diet;
sun exposure;
blood levels of 25(OH)D;
body weight;
intestinal absorption capacity;
renal function;
presence of diseases;
any pharmacological therapies.
In the general population, nutritional recommendations serve as a reference for intake, while in individuals with documented deficiency or specific clinical conditions, the correction strategy must be defined individually.
The Italian LARN indicate reference requirements that increase in older age groups, also reflecting the reduced cutaneous synthesis capacity and the increased risk of insufficient availability.
The forms and dosages used to correct a clinically significant deficiency must be established by the doctor, especially in the presence of renal insufficiency, hyperparathyroidism, granulomatous diseases, or other conditions that can modify vitamin D metabolism.
Diet and sun exposure
Diet can contribute to vitamin D intake, but few foods naturally contain significant amounts.
The main dietary sources include oily fish, some species of small oily fish, egg yolk and fortified foods.
Vegetable oils, nuts and many plant-based foods can be excellent sources of other nutrients, but they should not automatically be considered significant sources of vitamin D.
For example, linseed oil and almonds are nutritionally interesting foods, but they do not provide equivalent sources of vitamin D compared to oily fish or fortified foods.
For people following a vegan diet, the availability of naturally rich sources of vitamin D is even more limited. In these cases, the availability of fortified foods and supplements containing vitamin D2 or plant-based vitamin D3 can be particularly important.
Sun exposure contributes to cutaneous vitamin D synthesis, but there is no universally applicable exposure time for everyone.
Season, latitude, time of day, age, skin pigmentation and exposed surface area profoundly affect the amount produced. Furthermore, exposure to UV rays must always be balanced with the prevention of skin damage.
For this reason, it is not appropriate to provide a universal recommendation such as “ten or fifteen minutes of sun is enough” to ensure adequate vitamin status.
Lichen-derived vitamin D3 and vegan supplementation
The availability of lichen-derived vitamin D3 represents a major development in supplement formulation.
For those following a vegan diet, the option to take cholecalciferol from a non-animal source makes it possible to use the D3 form while remaining consistent with their dietary choices.
However, the choice of lichen-derived vitamin D3 does not change the fundamental principle of supplementation: even a vegan source must be used in a quantity appropriate to individual needs.
The origin of the ingredient is therefore an important feature in terms of formulation and dietary compatibility, while biological efficacy depends on the molecular form, dose, absorption and baseline vitamin status.
Bone health prevention: an integrated strategy
Bone health does not depend on a single nutrient.
Vitamin D acts within a network that includes calcium, adequate protein intake, physical activity, hormonal status, body composition and numerous other factors.
An effective prevention strategy therefore includes a balanced diet, adequate calcium and protein intake, maintaining appropriate vitamin D levels and regular physical activity.
Exercises involving mechanical loading and strength training can help maintain bone and muscle mass.
Physical activity also plays a key role in preventing sarcopenia and maintaining balance.
Frailty prevention should therefore be considered a system in which nutrition, movement, vitamin status and risk factor management work together.
Recognised vitamin D claims
In compliance with European regulations on nutrition and health claims, vitamin D can contribute to:
the normal absorption and use of calcium and phosphorus;
maintaining normal blood calcium levels;
maintaining normal bones;
maintaining normal muscle function;
maintaining normal teeth;
the normal function of the immune system.
These recognised effects form the most solid scientific and regulatory basis for describing the physiological role of vitamin D.
Research is also continuing to study the possible involvement of vitamin D in cardiovascular, metabolic, neurological and oncological health. In these areas, however, it is necessary to distinguish between biological plausibility, observational associations and proven clinical benefits.
An essential vitamin, but not a universal solution
Research in recent years has profoundly changed the way vitamin D is understood.
On the one hand, the discovery of the vitamin D receptor in numerous tissues has highlighted a much greater biological complexity than bone metabolism alone.
On the other hand, large clinical trials have shown that indiscriminate intake of high doses in the general population does not automatically lead to a reduction in mortality, cardiovascular events, cancer or other chronic diseases.
In the D-Health Trial, monthly administration of vitamin D3 to older adults not selected on the basis of a documented deficiency did not reduce mortality from all causes.
The most important message of contemporary research is therefore that of appropriateness.
Vitamin D is essential when it is needed to support its physiological functions and to correct a deficiency. However, it should not be presented as a universal treatment capable of indiscriminately preventing obesity, dementia, cancer or cardiovascular disease.
Individual assessment makes it possible to distinguish those people who may genuinely benefit from supplementation from those in whom an indiscriminate increase in dose offers no proven benefits.
In this context, lichen-derived vitamin D3 represents a particularly interesting solution because it makes it possible to supplement cholecalciferol through a source also suitable for a vegan diet.
Its value therefore lies in the combination of a form biologically utilized by the body, a non-animal origin, and the possibility of incorporating it into a personalized nutritional strategy.
The health of bones, muscles, and the immune system does not depend on a single supplement, but on the ability to maintain over time an adequate balance between diet, physical activity, environmental exposure, nutritional status, and individual characteristics.
Vitamin D is one of the fundamental elements of this balance.
PLEASE NOTE: The information in this article is for informational and educational purposes only and does not constitute medical advice. The published content is not intended to replace the doctor-patient relationship or any medical advice, diagnosis, or prescriptions. The assessment of vitamin D status and any supplementation must be personalized, particularly in the presence of medical conditions, pregnancy, kidney failure, osteoporosis, or pharmacological treatments.
Bibliographic references
- Manson JE, Cook NR, Lee IM, et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. New England Journal of Medicine. 2019;380:33-44. VITAL randomized study involving 25,871 participants, which did not show a significant reduction in the overall incidence of invasive cancers or major cardiovascular events with 2,000 IU/day of vitamin D3 in the studied population.
- Bischoff-Ferrari HA, Vellas B, Rizzoli R, et al. Effect of Vitamin D Supplementation, Omega-3 Fatty Acid Supplementation, or a Strength-Training Exercise Program on Clinical Outcomes in Older Adults: The DO-HEALTH Randomized Clinical Trial. JAMA. 2020. Randomized trial conducted on 2,157 older European adults.
- Neale RE, Baxter C, Romero BD, et al. The D-Health Trial: a randomised controlled trial of the effect of vitamin D on mortality. Lancet Diabetes & Endocrinology. 2022. Randomized trial on monthly vitamin D3 supplementation and mortality in older adults.
- Neale RE, et al. Vitamin D supplementation and major cardiovascular events: D-Health randomised controlled trial. BMJ. 2023;381. Analysis of cardiovascular events in the D-Health Trial.
- de Moura de Souza M, Dantas RLM, Durães VL. Vitamin D Supplementation and the Incidence of Fractures in the Elderly Healthy Population: A Meta-analysis of Randomized Controlled Trials. Journal of General Internal Medicine. 2024.
- Effectiveness of Vitamin D Supplements in Reducing the Risk of Falls among Older Adults: A Meta-Analysis of Randomized Controlled Trials. 2023. Meta-analysis of 17 randomized studies involving 38,598 older adults.
- Commission Regulation (EU) No. 432/2012 and subsequent consolidated versions. Register of health claims authorized in the European Union, including those related to vitamin D, calcium and phosphorus metabolism, muscle function, bones, teeth, and the immune system.
- Bouillon R, Marcocci C, Carmeliet G, et al. Skeletal and Extraskeletal Actions of Vitamin D: Current Evidence and Outstanding Questions. Reference literature on the physiological and extra-skeletal mechanisms of vitamin D.
- Bikle DD. Vitamin D: Newly Discovered Actions Require Reconsideration of Physiological Requirements. Trends in Endocrinology and Metabolism. 2010;21:375-384.
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- SINU. LARN – Nutrient and Energy Reference Intakes for the Italian Population. IV Revision and subsequent updates.
