Vitamin D is a hormone that is essential for our health. It promotes calcium absorption, regulates many immune functions and also appears to play a role in mental well-being.
People living in mountainous regions or areas with long winters, such as Switzerland, may experience deficiencies because the skin's production of vitamin D depends on sunlight. For this reason, interest in supplements and solariums is growing, but what is the scientific evidence behind these strategies? In this article, we explore the role of vitamin D, analyse the latest studies and suggest safe ways to maintain adequate levels.
Role of vitamin D in immunity
Vitamin D modulates immune system activity. It stimulates the production of antimicrobial peptides such as cathelicidin LL 37 and β defensins, molecules that help neutralise viruses and bacteria; it also regulates the action of macrophages, T and B lymphocytes, contributing to a balance between pro- and anti-inflammatory responses. Observational studies link low vitamin D levels to an increased risk of respiratory infections. However, the largest meta-analysis in recent years, based on 43 randomised clinical trials, found no significant reduction in respiratory infections with vitamin D supplementation. A modest benefit appears when vitamin D is taken daily in moderate doses (400–1,200 IU), especially during the cold months. This means that an adequate intake of vitamin D supports the body's defences, although it does not guarantee protection against flu or colds.
Vitamin D and mental health
In recent years, research has also investigated the link between vitamin D and mood. A meta-analysis published in 2025 on twenty randomised studies showed that vitamin D supplementation can moderately but statistically significantly reduce depressive symptoms compared to placebo. The benefits appear to be more evident in people with deficiencies and depend on the dose and duration of supplementation: cycles of at least eight weeks and doses between 2,000 and 4,000 IU/day were associated with more marked improvements. However, it is important to interpret these data with caution, as the studies considered are heterogeneous and do not replace a personalised therapeutic approach.
For those seeking a mood boost, exposure to light and adequate vitamin D can be adjuncts to a broader wellness programme that includes physical activity, a balanced diet and, if necessary, medical support.
Vitamina D, ossa e muscoli
The best-known function of vitamin D is bone mineralisation. Adequate levels of 25 OH vitamin D (≥ 50 nmol/L) are essential for preventing rickets in children and osteomalacia in adults. The National Institutes of Health (NIH) considers 50 nmol/L to be the minimum value for bone and muscle health, while levels above 125 nmol/L can cause adverse effects such as hypercalcaemia and kidney stones.
Clinical studies show that, in the general population, high doses of vitamin D do not improve bone mineral density compared to placebo; a slight benefit is only observed in those with a marked deficiency. A 2024 meta-analysis also found that taking 800–1,000 IU of vitamin D per day reduces the risk of falls in older adults, especially when initial levels are low and when the vitamin is taken daily. Higher doses do not provide additional benefits and may, in fact, increase the risk of falls.
How to obtain vitamin D
The body produces vitamin D from 7-dehydrocholesterol thanks to UVB rays. The most natural method is exposure to the sun: 5–30 minutes of exposure of the hands, arms and face, two or three times a week, avoiding the middle of the day to prevent sunburn. However, in winter or in regions with little sunshine, this synthesis is limited.
Alternative sources may be useful here:
- Food: fatty fish (salmon, mackerel), fortified milk, eggs and mushrooms provide vitamin D, albeit in modest amounts.
- Supplements: Formulations ranging from 400 to 1,000 IU per day are sufficient for most adults. It is advisable to check serum levels before taking higher doses.
- Exposure to UVB lamps: controlled clinical studies have shown that four short exposures to UVB lamps significantly increase vitamin D levels in deficient individuals without altering inflammatory markers. This method, used in medical settings or professional solariums, can be effective during the dark months. It is essential that sessions are personalised, gradually increased and supervised to avoid skin damage.
Safety recommendations
The research emphasises the importance of moderation. While vitamin D is essential, excess intake – whether through supplements or exposure to UV rays – can cause toxicity. Self-administration of high doses without medical supervision is therefore not recommended, nor is the use of solariums as a 'universal cure'. The World Health Organisation and dermatologists remind us that excessive exposure to UV rays can increase the risk of skin cancer. For this reason, BlueLight focuses on the health and well-being of its customers, promoting conscious, safe and personalised use of solariums.
At BlueLight centres, each exposure cycle is calibrated on an individual basis and always accompanied by SkinControl, a visual and instrumental skin check that helps prevent abnormalities and assess suitability for exposure. Choosing reputable facilities with certified equipment, competent staff and a genuine focus on health is essential for reaping the benefits of light without taking risks.
In this sense, BlueLight is not just a place to expose yourself to light: it is a reliable partner on your journey to wellness.
In conclusion, vitamin D is a valuable ally for overall well-being: it supports immunity, contributes to bone and muscle health, and can also support mood. Scientific evidence indicates that maintaining adequate levels is important, while high doses or uncontrolled exposure do not provide additional benefits and can be harmful. The safest and most sustainable approach combines controlled exposure to light – sunlight or UVB lamps – with a balanced diet and, when necessary, targeted supplementation. In the dark months or in areas with little sunshine, solariums can be a valuable resource, but only if used wisely. In this sense, BlueLight is committed to offering a service based on expertise, safety and personalisation, with calibrated exposure cycles, certified equipment and the support of SkinControl for skin health protection.
Would you like to discover how light can truly contribute to your wellbeing? Visit us at one of our BlueLight centres: you will receive a personalised analysis and be guided step by step along a safe, enjoyable and tailor-made journey. Contact us today to rediscover the energy of light, with awareness.
Authoritative bibliographical sources and scientific insights
Wang C H et al., Optimal methods of vitamin D supplementation to prevent acute respiratory infections: a systematic review, dose–response and pairwise meta analysis – Nutrition Journal, 2024 nutritionj.biomedcentral.com.
Disponibile su: https://nutritionj.biomedcentral.com/articles/10.1186/s12937-024-00990-w
Mo C et al., A pilot clinical trial to explore the effects of UV exposure on vitamin D synthesis and inflammatory responses in vitamin D deficient adults – Scientific Reports, 2025 pmc.ncbi.nlm.nih.gov.
Disponibile su: https://pmc.ncbi.nlm.nih.gov/articles/PMC12217245/
LeBoff M et al., Effects of Supplemental Vitamin D on Bone Health Outcomes in Women and Men in the VITamin D and OmegA 3 TriaL (VITAL) – Journal of Bone and Mineral Research, 2020 pmc.ncbi.nlm.nih.gov.
Disponibile su: https://pmc.ncbi.nlm.nih.gov/articles/PMC7217747/
Tan L et al., Effect of vitamin D, calcium, or combined supplementation on fall prevention: a systematic review and updated network meta analysis – BMC Geriatrics, 2024 bmcgeriatr.biomedcentral.com.
Disponibile su: https://bmcgeriatr.biomedcentral.com/articles/10.1186/s12877-024-05009-x
NIH Office of Dietary Supplements, Vitamin D – Fact Sheet for Consumers ods.od.nih.gov.
Disponibile su: https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
Wang L et al., Meta-analysis of the effect of vitamin D on depression – Frontiers in Psychiatry, 2025 pmc.ncbi.nlm.nih.gov.
Disponibile su: https://pmc.ncbi.nlm.nih.gov/articles/PMC12352333/
