The Government should immediately change recommendations for vitamin D supplements as a matter of urgency by urging all adults to take them during the coronavirus pandemic, according to scientists at Trinity College Dublin.
This follows evidence highlighting the association between vitamin D levels and mortality from Covid-19 produced by Dr Eamon Laird and Prof Rose Anne Kenny, who lead the Irish Longitudinal Study on Ageing.
They analysed European adult population studies completed since 1999 which measured vitamin D, and compared vitamin D and death rates from Covid-19.
The pivotal role of vitamin D in fighting viral infections is known but it can also “support the immune system through a number of immune pathways” involved in fighting Covid-19, they conclude in a study published in the Irish Medical Journal.
The correlation is so strong taking vitamin D should be advised immediately, Prof Kenny said. This was because vitamin D deficiency was common among those at risk of Covid-19 (particularly older people); there was no toxic risk from taking it at the recommended dosage level, and growing evidence of benefits.
Last week, scientists at Northwestern University in the US found those with severe vitamin D deficiency were twice as likely to experience Covid-19 complications.
If changing advice led to a rush of products on sale in shops, “it is not a reason not to take it . . . This is no time to hang around”, she added.
“While there are currently no results from randomised 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.”
In England, Scotland and Wales, public health bodies have revised recommendations since the Covid-19 outbreak to say all adults should take at least 400 IU (international units) of vitamin D daily.
Prof Kenny said most scientists would recommend between 800 and 1,000 IU – she takes the higher dose – and recommended older people be exposed to 10 to 15 minutes of sunshine daily, if possible.
Vitamin D is produced in the skin from UVB sunlight exposure. It is changed into an active hormone that keeps the skeleton strong and free of osteoporosis. It is also contained in many foods, such as oily fish and cheese, while most people ensure they have adequate amounts through a combination of sunlight and a healthy diet.
Controversially, US president Donald Trump suggested zapping the virus with sunlight or UV but this was not related to the vitamin D connection in boosting the immune system.
In response to the study, a Department of Health spokeswoman said the National Public Health Emergency Team which advises the Government on Covid-19, "keeps all national and international evidence and advice under continuous review as the basis for any recommendations".
The TCD data, produced in collaboration with Prof Jon Rhodes at the University of Liverpool, suggests it is likely to reduce serious Covid-19 complications. "This may be because vitamin D is important in regulation and suppression of the inflammatory cytokine response, which causes the severe consequences of Covid-19 and 'acute respiratory distress syndrome' associated with ventilation and death," Prof Kenny explained.
Cytokine storms seem to kill a majority of Covid-19 patients, and not destruction of the lungs by the virus itself.
This study shows – counterintuitively – countries at lower latitude and typically sunny countries, such as Spain and northern Italy, had low concentrations of vitamin D and high rates of deficiency. These countries also experienced the highest Covid infection and death rates in Europe.
Northern latitude countries (Norway, Finland and Sweden) have higher vitamin D levels despite less UVB sunlight exposure, because supplementation and fortification of foods is more common. These countries have lower Covid infection and death rates.
Vitamin D deficiency is common in Ireland and is most prevalent with age, obesity, in men, in ethnic minorities, in people with diabetes, hypertension and in nursing homes.
Dr Laird said: “Optimising vitamin D intake to public health guidelines will certainly have benefits for overall health and support immune function. 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.
“Supplementation is the best means of ensuring sufficient vitamin D blood levels. As the effects of coronavirus continue, many of us are limited in the time we can spend outdoors, so extra care is required to keep vitamin D levels healthy.”