Analysis: a huge number of studies have shown strong links between Vitamin D deficiency and risk of Covid-19 infection

By Daniel McCartneyTU DublinPaula M. O'SheaNUI GalwayJohn FaulConnolly Hospital BlanchardstownMartin HealyTCDGreg ByrneTU DublinTomás GriffinNUI GalwayCathal WalshUniversity of LimerickJ Bernard WalshSt. James's Hospital, DublinDeclan ByrneSt. James's Hospital, Dublin and Rose Ann KennyTCD

The current pandemic has both convulsed world economies and crippled societies and seen an unprecedented mobilisation of the global scientific community in search of an effective vaccine. While this is a profoundly important scientific endeavour, it would be wrong to assume that vaccination is the only show in town when it comes to suppressing this virus.

We started writing about the links between vitamin D and Covid-19 in March 2020, long before the SARS-CoV-2 virus was fully characterised. We knew from early in the pandemic that death rates from Covid-19 were alarmingly high amongst Black, Asian and Minority Ethnic (BAME) communities. We also knew that those who were older or obese were much more likely to have a poor outcome or die if they became infected. So this led us to question what common factor might be responsible for this increased risk among these seemingly disparate groups?

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Ó RTÉ Raidió na Gaeltachta's Adhmhaidin, creideann Dr Illona Duffy go láidir go bhfuil leas le fáil as a bheith ag tógáil Vitamín D mar chosaint in aghaidh an víris

One possible explanation was vitamin D. Humans acquire vitamin D mainly from summer sunlight exposure, but also from food and supplements. It's well established that some groups are more likely to be deficient: older people; those with darker pigmentation because their skin makes vitamin D less efficiently in response to sunlight, and those with obesity because vitamin D gets locked away within their body fat.

This really matters in a viral pandemic, as vitamin D is critically important in helping our immune system to resist viral infection, and to limit inflammation when infection does occur. When these arms of the immune system malfunction it’s a perfect storm. There is a greater risk of becoming infected, and greater risk of a severe inflammatory response to the infection; exactly the kind of uncontrolled inflammation that kills people with Covid-19. 

Studies began to emerge last April showing higher Covid-19 infection and death rates in countries with lower population vitamin D levels. These aligned with earlier studies showing that those with low vitamin D levels were more likely to get respiratory infections, and correspondingly, that supplementing deficient individuals with vitamin D helped them to avoid these lung infections. At around this time, hospital data from very sick Covid-19 patients also revealed a characteristic type of severe inflammation that was suggestive of vitamin D deficiency.

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From ABC News, Dr. L. Ray Matthews discusses research looking into the potential impact of vitamin D in the fight against the coronavirus

By May, the first studies explicitly examining the links between vitamin D and Covid-19 began to surface. One study from Connolly Hospital in Blanchardstown showed lower vitamin D levels in Covid-19 patients admitted to the intensive care unit (ICU), and also that those with low vitamin D levels were more than three times more likely to require ventilation.

These findings were soon corroborated by others. A German study showed that not only did hospitalised Covid-19 patients have lower vitamin D levels than less sick Covid-19 outpatients, but that hospitalised inpatients who were vitamin D deficient were roughly 15-times more likely to require intensive care treatment, and over 6 times more likely to die from Covid-19 than those with sufficient vitamin D levels. Several studies also emerged from the US and Israel over the summer highlighting higher Covid-19 infection rates in those with low vitamin D levels.

While these are persuasive findings however, do they really show that low vitamin D is causally implicated in Covid-19? And could supplementing with vitamin D really help patients survive Covid-19 infection? These questions have been addressed over the past two months by two small studies, one from Spain and one from France.

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From ABC News' Good Morning America, medical correspondent Dr. Jen Ashton on the potential benefits of vitamin D in protecting people against Covid-19

The Spanish study showed that just 2% of Covid-19 patients receiving activated vitamin D on admission and over their first week in hospital were admitted to ICU versus 50% of patients who weren’t given vitamin D. Statistically, this 25-30-fold decreased risk of ICU admission is considerably better than that achieved using several drugs recently repurposed to treat Covid-19. The French study showed that the survival rate of elderly nursing home patients with Covid-19 five weeks after leaving hospital was 83% amongst those given large doses of vitamin D prior to discharge versus 44% in those who didn’t receive it.

How does this relate to Ireland? Well, around half of all adults in Ireland are deficient in vitamin D, with severe deficiency especially prevalent amongst our older adults. For example, the TILDA study revealed that up to 37% of community-based adults aged 70 years and over had profound vitamin D deficiency. In a further recent study from Galway, 42% of nursing home residents, the group who have suffered about half of the total Covid-19 deaths recorded in Ireland, were shown to be profoundly deficient. Even amongst younger adults, low vitamin D levels are very common, with just under half of 18 to 39 year olds in Dublin deficient, and about one in five profoundly deficient.

Even amongst younger adults, low vitamin D levels are very common, with just under half of 18 to 39 year olds in Dublin deficient

The high prevalence of deficiency in this country is living proof that optimal vitamin D levels cannot be achieved through our low sunlight exposure and poor dietary intakes alone. This highlights the need for supplementation across the population. For Irish adults, much evidence now suggests that supplementation at 20-25 micrograms per day (1000 IU/day) is required to enhance immune function. Supplementation at higher doses under medical supervision is likely to be needed for obese individuals, those with darker skin or older adults. 

Given the recent findings linking vitamin D deficiency and Covid-19 risk, and in light of our high prevalence of deficiency, especially in winter; it’s imperative that public health advice addressing this issue is now urgently developed to help address the worst effects of this pandemic.

Dr Daniel McCartney is a lecturer at the School of Biological and Health Sciences at TU Dublin. Dr Paula M. O'Shea is a Consultant Clinical Biochemist at the School of Medicine at NUI GalwayProf. John Faul is a Consultant in Respiratory and Sleep Medicine at the Royal College of Surgeons in Ireland's James Connolly Memorial Asthma Research Centre in Connolly Hospital BlanchardstownDr. Martin Healy is Principal Clinical Biochemist in the Department of Biochemistry at St. James's Hospital, Dublin and Adjunct Assistant Professor in the Department of Medical Gerontology in the School of Medicine at TCDDr Greg Byrne is a lecturer in the School of Biological and Health Sciences at TU DublinDr. Tomás Griffin is a Consultant in Endocrinology at the Centre for Endocrinology, Diabetes and Metabolism at Galway University Hospitals and a Researcher at the Regenerative Medicine Institute at CÚRAM SFI Research Centre at the School of Medicine at NUI GalwayProf. Cathal Walsh is a HRB Research Leader in Health Decision Science at the Department of Mathematics and Statistics at the University of LimerickProf. J Bernard Walsh is a Clinical Professor in TCD and the founder of the Mercer's Institute’s Bone Health and Osteoporosis Treatment Unit in St. James's Hospital, DublinProf. Declan Byrne is Clinical Director for Medicine at St. James's Hospital, Dublin and Clinical Associate Professor in Medical Gerontology at TCDProf Rose Ann Kenny holds the Chair of Medical Gerontology and is Head of the academic department of Medical Gerontology at TCD. She is an Irish Research Council awardee.


The views expressed here are those of the author and do not represent or reflect the views of RTÉ