Light in the Context of Health: The COVID-19 Pandemic

In October 2025, Prof. Stefan Pilz delivered his lecture “Vitamin D, sunlight exposure and COVID-19: how evidence-based medicine was applied” at the Vitamin D: EVIDAS 2025 conference in Warsaw, reminding the audience that: “The COVID pandemic is considered the greatest health crisis of the 21st century, with an enormous impact on public health, economy, politics, and our society in general.”

He added: “Never in history before did science on a particular disease attract so much attention and was used to guide – or you could say, dictate – so many aspects of the life of the general population.”

This presentation once again drew attention to a study published in Health & Place (2024), in which a team led by Richard Weller and Chris Dibben from the University of Edinburgh reported an association between higher exposure to ultraviolet (UV) radiation (both natural and artificial) and lower all-cause mortality in the studied population. We have already written about this study earlier on our blog.

Prof. Pilz referred to these findings, emphasising that they may be associated with the functioning of the immune system and the body’s response to infections, including COVID-19.

Light and immunity: Lessons from the pandemic

“We have to learn from this pandemic as we have to learn from our history.”

The COVID-19 pandemic highlighted the importance of environmental factors such as daylight, circadian rhythm, physical activity, and vitamin D levels. Periods of confinement and shorter days in the Northern Hemisphere led to reduced vitamin D levels in many populations, which may have been associated with changes in immune system function.

At the time, analyses (e.g. Cherrie et al., British Journal of Dermatology, 2021) suggested that regions with lower levels of UVA radiation experienced higher COVID-19 mortality, independently of vitamin D levels. This indicated that light may influence the immune system through multiple pathways, not only via vitamin D synthesis but also through vascular and immunological mechanisms.

Findings from the UK Biobank

Prof. Pilz summarised data from over 395,000 participants in the UK Biobank cohort:

“The mortality, the all-cause mortality and also the cause-specific mortality, was significantly lower in those with more UV exposure, being at sunbed use or being at the residential UV radiation exposure, compared to no sunbed use or lower UV exposure.”

“With regard to melanoma, there was no significant increase in those with solarium use versus no use.”
“I’m not promoting here sunbeds. I’m just telling you what the science from these observational studies found out with regard to the association of UV exposure and health outcomes.”

Mechanisms – beyond Vitamin D

UV radiation activates biological processes in the skin that are associated with the functioning of the immune system:

• UVB radiation stimulates the production of vitamin D in the skin, which is associated with immune function, including the activity of immune cells and the regulation of inflammatory processes.
• UVA radiation stimulates the release of nitric oxide (NO), a compound that dilates blood vessels, improves circulation, and is associated with the regulation of inflammatory processes. NO may influence the regulation of the NLRP3 inflammasome, a mechanism involved in chronic inflammation and more severe courses of viral infections, such as COVID-19.

As a result, sunlight may be one of the factors influencing immune system function in ways that extend beyond vitamin D supplementation alone.

Tanning beds as a model of controlled exposure

It is important to note that in the UK Biobank study, tanning bed use was not considered a preventive measure, but rather an indicator of exposure to UV radiation.

“We still have to wait for interventional trials for UV exposure, probably using sun-tanning beds and so on. But I think it’s worth looking at it.”

In this context, tanning beds can serve as a research model, a way to study how the body responds to different UV wavelengths and dosing under controlled conditions.

This is not about promoting tanning, but about better understanding the biology of light and its relevance to immune function.

Light in preventive health

Both epidemiological data and Prof. Pilz’s lecture point to the need for balance in our approach to sunlight.

Excessive exposure can lead to sunburn and DNA damage, while overly restrictive avoidance of light may be associated with changes in immune function and overall health.

The pandemic showed that prolonged time spent in low-light indoor environments may have a negative impact on well-being and physiological functioning.

Modern prevention should therefore include a conscious approach to light: short exposures, regularity, and adaptation to skin phototype and local UV Index.

Conclusions

1. Exposure to UV radiation, whether natural or controlled, is in observational studies associated with various health-related outcomes, including all-cause mortality.
2. These associations may involve mechanisms related to vitamin D as well as other biological processes, such as UVA and nitric oxide pathways.
3. In population studies, tanning bed use has served as an indicator of UV exposure, but requires safe and responsible use.
4. The COVID-19 pandemic highlighted the importance of environmental factors, including light, in the context of health and human functioning.