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COVID-19 mortality increases with northerly latitude after adjustment for age suggesting a link with ultraviolet and vitamin D.

Take Home Message

This study investigated the relationships between latitude, age of population, population density and pollution with COVID-19 mortality. The proportion of older people in each country impactedCOVID-19 mortality, but after adjustment for proportion of older people in the population, a strong association remained across the Northern hemisphere for higher COVID-19 mortality at higher latitudes where populations commonly get insufficient ultraviolet B to maintain normal vitamin D blood levels throughout winter.

 

Results

  • The analysis supported the hypothesis with a threshold of 28° north, above which deaths increased in a linear manner.
  • An age adjustment was highly significant, with an estimated mortality increase of 13.7% for each 1% increase in the percentage of people ≥65 years of age.
  • Latitude was also significant with an estimated 4.4% increase in mortality for each 1° further north.
  • Countries with higher pollution included many with younger populations, and pollution was negatively associated with mortality but added no significant explanatory power to a model containing latitude and age.
  • Population density expressed per country was not significantly associated with mortality.

Who

COVID-19 deaths from 117 countries with a population of >1 million and with ³150 COVID-19 cases.

Things to Keep in Mind

  • Because this study is an ecological study that is based on population data, the results do not mean that individuals with vitamin D deficiency are at an increased risk of COVID-19 infection and mortality.
  • Since this study is based on early data from the pandemic (until May 18, 2020), it would be useful for the data to be reanalyzed, taking into account the larger datasets now available and the seasonal variation in cases observed during the past year to confirm whether the latitude threshold hypothesis is still valid.
  • A direct effect of ultraviolet light on the environmental survival of SARS-CoV-2 is also possible, but would not explain the association between mortality and ethnicity, whereas people with dark skin need more ultraviolet exposure for equivalent vitamin D synthesis.

Author’s Conclusions

The proportion of older people in each country impacts greatly on COVID-19 mortality, but after adjustment for this, a strong association remains across the Northern hemisphere between latitude and higher COVID-19 mortality. This association exists above 28° north not far from the latitude, usually stated as 35° north, beyond which populations commonly get insufficient ultraviolet B to maintain normal vitamin D blood levels throughout winter. There are exceptions, but COVID-19 mortality correlates with reported vitamin D levels across Europe, and in sunnier Brazil, where mortality is rising, 28% prevalence of vitamin D deficiency is reported.

Study Design

  • The hypothesis of this study was that there would be no relationship between mortality and latitude below a threshold and that mortality would increase with latitude above that threshold.
  • COVID-19 mortality per million by country was downloaded from the website Worldometer on May 18, 2020. All 117 countries with a population >1 million and ≥150 COVID-19 cases were included.
  • Data by country for population percentage ≥65 years (%³65), population density, and air pollution (particles of matter <2.5 um diameter μg/m3) were obtained from public sources.
  • Latitude was entered for the capital city of each country.
  • Mortality data were log transformed, and piecewise linear modeling was used to explore the relationship with latitude. This was adjusted for population percentage ≥65, and pollution and population density were investigated to see if they further explained variability in mortality.

Reference

Rhodes J, Dunstan F, Laird E, Subramanian S, Kenny RA. COVID-19 mortality increases with northerly latitude after adjustment for age suggesting a link with ultraviolet and vitamin D. BMJ Nutr Prev Health. 2020 Jun 14;3(1):118-120. doi: 10.1136/bmjnph-2020-000110. PMID: 33235975; PMCID: PMC7664496.

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2021-07-06T16:03:23-05:00