Ultraviolet A radiation and COVID-19 deaths in the USA with replication studies in England and Italy

Br J Dermatol. 2021 Aug;185(2):363-370. doi: 10.1111/bjd.20093. Epub 2021 May 31.


Background: Understanding factors impacting deaths from COVID-19 is of the highest priority. Seasonal variation in environmental meteorological conditions affects the incidence of many infectious diseases and may also affect COVID-19. Ultraviolet (UV) A (UVA) radiation induces release of cutaneous photolabile nitric oxide (NO) impacting the cardiovascular system and metabolic syndrome, both COVID-19 risk factors. NO also inhibits the replication of SARS-CoV2.

Objectives: To investigate the relationship between ambient UVA radiation and COVID-19 deaths.

Methods: COVID-19 deaths at the county level, across the USA, were modelled in a zero-inflated negative-binomial model with a random effect for states adjusting for confounding by demographic, socioeconomic and long-term environmental variables. Only those areas where UVB was too low to induce significant cutaneous vitamin D3 synthesis were modelled. We used satellite-derived estimates of UVA, UVB and temperature and relative humidity. Replication models were undertaken using comparable data for England and Italy.

Results: The mortality rate ratio (MRR) in the USA falls by 29% [95% confidence interval (CI) 40% to 15%) per 100 kJ m-2 increase in mean daily UVA. We replicated this in independent studies in Italy and England and estimate a pooled decline in MRR of 32% (95% CI 48% to 12%) per 100 kJ m-2 across the three studies.

Conclusions: Our analysis suggests that higher ambient UVA exposure is associated with lower COVID-19-specific mortality. Further research on the mechanism may indicate novel treatments. Optimized UVA exposure may have population health benefits.

MeSH terms

  • COVID-19*
  • Humans
  • Italy
  • RNA, Viral
  • SARS-CoV-2
  • Ultraviolet Rays / adverse effects
  • United States / epidemiology


  • RNA, Viral