A recent metanalysis by researchers from Trinity College Dublin indicates an association between low circulating levels of vitamin D and mortality from COVID-19, and has doctors calling the government to increase the recommended daily intake for vitamin D across the continent.
The article, published this week in the Irish Medical Journal, analyzed all European adult population studies, completed since 1999, which measured vitamin D and compared vitamin D levels and death rates from COVID-19 across geographic locations.
The authors found that locations where rates of vitamin D deficiency were the highest also had the highest COVID-19 mortality rates. The correlation between low vitamin D levels and death from COVID-19 is statistically significant.
Curiously, rates of vitamin D deficiency were highest at lower latitudes where climates are typically sunny like Spain and Northern Italy. Conversely, vitamin D deficiency rates were lowest among the Nordic countries of Norway, Finland and Sweden where UVB exposure is limited.
Presumably these northern latitude countries have higher vitamin D levels despite less UVB sunlight exposure, in part because supplementation and fortification of foods is more common, but age, obesity, diabetes, various cholesterol lowering drugs, gastric bypass surgery, the widespread use of sunscreens, and having darker skin tone also contribute to low vitamin D levels globally.
Although the relationship between vitamin D and COVID-19 infection remains unclear, the authors argue that many recent studies confirm the role of vitamin D in fighting viral infections.
“Whereas there are currently no results from randomized controlled trials to conclusively prove that vitamin D beneficially affects COVID-19 outcomes, there is strong circumstantial evidence of associations between vitamin D and the severity of COVID-19 responses, including death," said study co-author Rose Ann Kenny. Kenny and her colleagues feel that increasing vitamin D levels would have many health benefits while carrying little risk, and that the COVID crisis is a wakeup call for Ireland to revise its current guidelines for vitamin D supplementation to coincide with that of other countries.
"In England, Scotland and Wales, public health bodies have revised recommendations since the COVID-19 outbreak. Recommendations now state that all adults should take at least 400 IU vitamin D daily," Kenny said.
In the United States for example, despite fortification of Milk and Orange juice, many experts still feel that most adults aren’t getting enough vitamin D – especially in elderly, minority and obese populations. The Institute of Medicine set the RDA for adults at 600IU daily, and the Mayo Clinic recommends
that adults get at least that amount but argues that between 1000 and 2000 IU of vitamin D is safe. The Endocrine Society recommends between 1500 to 2000 IU for adults who may be deficient.
As for COVID, there’s no question that much more research is needed to illuminate the link between vitamin D levels and mortality rates, but researchers in the US have come to similar conclusions as the team in Ireland. Just a few weeks earlier a team of scientists from Northwestern published a pre-print study
(not yet peer reviewed) on medRxiv arguing that C Reactive Protein is a surrogate marker for severe COVID-19 and is associated with Vit D deficiency, and that Vit D may reduce COVID-19 severity by suppressing cytokine storm in COVID-19 patients.
Research like this is still exploratory and we need further trials to have concrete evidence on the level of vitamin D that is needed for optimal immune function,” said study co-author Eamon Laird. “However, studies like this also remind us how low our vitamin D status is in the population (even in sunny countries) and adds further weight to some sort of mandatory vitamin D fortification policy. If the Nordic countries are allowed to do this, there is no reason Ireland, the UK or rest of Europe can't either."