Vitamin D Status & COVID-19
Vitamin D influences several immune pathways, with the net effect of boosting mucosal defences in our lung tissue while simultaneously dampening excessive inflammatory responses.
What is noticeable about COVID-19 is the huge variation in the way it affects different populations. The number of reported cases and mortality rates appear to be oddly contrasting between countries and even between regions in the same country. I have previously detailed the effects of COVID-19. Comparisons between countries are difficult due to different reporting strategies, surveillance networks and case definitions. This has been neatly demonstrated by Belgium who have the highest numbers of deaths per capita in the EU (69 deaths per 100,000 population). This figure is noticeably higher than many other countries.
From the start of their outbreak in Belgium they have accounted for all deaths in all settings and included people who were also suspected of dying of COVID-19 without a confirmed diagnosis.
Black, Asian and minority ethnic communities are more profoundly affected by COVID-19
Ultimately how the disease affects people after exposure will of course depend on their age, health status, genetic heritage and race. A concerning variable is the emerging evidence of how COVID-19 affects black, Asian and minority ethnic communities (BAME) even though they make up only 14% of the UK population. On May 1st, 2020, the UK’s Institute for Fiscal Studies (IFS) published a report, which found that people from ethnic minorities despite being younger on average than the white British population were found to have much higher mortality rates.
After adjusting for age, gender and geographical factors it was concluded that COVID-19 death rates for people of African descent was 3·5 times higher, while those people of Caribbean and Pakistani descent were 1·7 times and 2·7 times higher respectively. In an article published this week (reported in the Guardian) in the Journal of European Clinical Nutrition the authors comment that in Chicago more than half of COVID-19 cases and around 70% of COVID-19 deaths were of African American extraction. Meanwhile in Sweden it has been reported that 40 % of the reported COVID-19 related deaths occurring in Stockholm were from Somali communities and yet they only represent 0.84% of the population. This was reported in the British Medical Journal.
Analysis in the UK demonstrated that of 106 deaths in health workers two thirds (or 63%) were in BAME ethnic groups (up to April 22, 2020). Alarmingly this figure rose even higher for doctors (94%) and nurses (71%) . This is despite only 40% of doctors and 20% of nurses coming from BAME backgrounds. While socio-economics, health status and cultural aspects (such as dress codes) unfortunately play their part, it is now obvious that an explanation is more complex. Dame Donna Kinnair, chief executive and general secretary of the Royal College of Nursing, commented “Our fears that disproportionate numbers of nursing staff, as well as patients, from black and Asian communities are dying from the virus are well-founded. It is also very worrying that the Office of National Statistics states that the higher death rate cannot simply be explained by socio-economic disadvantage. We urgently need more research to be commissioned into what factors are causing this impact on black and Asian communities.” In medical journals meanwhile there is growing speculation about the influence of vitamin D deficiency which is known to have an important role for our immune status. The British Medical Journal (BMJ) and The Lancet have all recently published articles in relation to this point.
Even before COVID-19 respiratory tract infections were a major cause of global mortality. In fact, pre-COVID, estimates suggested that respiratory tract infections (RTI) were generally responsible for 2.65 million deaths in 2015 and approximately 10% of admissions to emergency departments in the U.S. The drive to increase our knowledge and understanding of RTIs has been of great scientific interest. Epidemiological studies meanwhile have also reported a strong correlation between vitamin D deficiency, viral respiratory tract infections and acute lung injury.
Vitamin D deficiency is a Global Heath Concern
Vitamin D deficiency is a global public health concern and it has been estimated that more than one billion people worldwide have some form of deficiency. How much sunlight we receive and absorb matters because vitamin D is not readily available nutritionally. The chart below gives some indication of what is required in terms of minutes of sunshine exposure in different parts of the world to top up our daily dose of vitamin D (depending on how dark our skin tone is). About 10% of people in the UK have inadequate amount of vitamin D levels in the summer, rising to nearly 40 per cent during the winter months. For this reason, in 2016, the UK’s Scientific Advisory Committee on Nutrition recommended that everyone should consider taking vitamin D supplements during winter.
Vitamin D is synthesised in skin during exposure to ultraviolet radiation in sunlight. Increased skin pigmentation reduces the efficacy of UV light because melanin functions as a natural sunblock. In addition, aging decreases the ability of the skin to produce vitamin D.
During the winter months countries at latitudes of above 40° receive little or no UV light. Therefore, if we live at high latitude, this increases the risk of vitamin D deficiency during the winter. This is likely compounded by age and skin pigmentation.
However, even living at low latitudes does not guarantee adequate vitamin D levels. Social and cultural factors may limit sun exposure. Vitamin D deficiency is particularly common in Middle Eastern girls and women. Furthermore, despite abundant sunlight throughout the year in Ecuador, vitamin D deficiency was reported to be common among elderly women.
Our Immune System and Vitamin D
Vitamin D influences several immune pathways, with the net effect of boosting mucosal defences in our lung tissue while simultaneously dampening excessive inflammatory responses. It prevents excessive inflammation by moderating the effect of chemical messengers called cytokines. These tiny proteins are released by cells to have specific effect on other cells. They often generate a cascade, as one cytokine stimulates its target cells to make additional cytokines and so on and so forth.
There are different types of cytokines such as interferons, interleukins, lymphokines and tumour necrosis factor (TNF). They are collectively responsible for triggering some familiar symptoms that arise when your body fights an infection, such as fever, inflammation and pain.
COVID-19 is known to generate an overproduction of cytokines in what is known as a ‘cytokine storm’. This generates persistent and severe inflammation in the lungs (hence the term severe acute respiratory syndrome or SARS) and other organs leading to multiple organ failure.
Vitamin D not only helps to dampen the collective effect of this cascade, but it also attenuates the effect of macrophages. These are specialised cells involved in the detection and destruction of harmful organisms such as a virus. During persistent periods of inflammation macrophages can be detrimental. Vitamin D not only serves to act as an important handbrake for cytokines and macrophages, it boosts the defences of our mucosal linings in our respiratory tracts. Clearly the epithelial cells in our mucosal linings in our respiratory tracts is the front line in pneumonia. Vitamin D enhances cellular immunity partly in these cells through inducing the production of tiny protein fragments (peptides) called cathelicidin, and defensins. Cathelicidins have direct antimicrobial activities against a spectrum of bacteria, enveloped and non-enveloped viruses,
Evidence supporting the role of vitamin D in reducing risk of COVID-19 includes that in the northern hemisphere the outbreak occurred in winter, a time when vitamin D status is low. Meanwhile the number of cases in the Southern Hemisphere near the end of summer are low. Australia, with a population of 25 million, has had just over 6,000 infections, and 50 deaths. New Zealand, a country of 5 million people, which closed its borders the day before Australia, has had 1,200 infections and so far only one death from Covid-19. All things considered vitamin D status could be a significant contributing factor in COVID-19 infection, progression, severity, and mortality. Vitamin D blood finger prick spot tests are cheap and vitamin D supplementation for at risk populations could be achievable.