These were the key takeaways from a presentation given by Philip Calder, professor of nutritional immunology at the University of Southampton, at last week’s Nutrition Society summer conference.
Regarding the evidence to support vitamin D supplementation to reduce the risk of COVID-19, he emphasised: "The association studies individually all tell the same story, and the meta-analysis almost completely supports that there’s an association between low status or deficiency and poor outcome.”
“So, our interpretation is that it may be better to have optimal vitamin D status before exposure to the virus. Whether it can be used to improve outcome in those already hospitalised with COVID-19 is uncertain,” he summarised, whilst drawing similar conclusions for zinc and selenium supplementation.
Calder emphasised the importance of immunity in the modern day: “The main findings from Covid-19 were that we are still at risk from pathogens. Weak immune systems were exposed as a major public health challenge in 2020.”
He asserted one main cause of weakened immunity is immunoscenesence, a process of immune dysfunction that occurs with age which results in a reduced production of immune cells, reduced circulating T cells, and poor response of memory cells to antigens with increasing age.
He said that older people are at a heightened risk of hospitalisation, poor vaccination response, and fatality following infection due to this, with data from Our World in Data observing that fatalities due to COVID-19 increased with age, particularly those over 60 years. In addition, a study found lower frequencies of neutralizing antibodies in response to the Pfizer COVID-19 vaccine in the elderly group, compared to those aged under 60.
“It turns out that the adverse effects of aging are made worse by frailty,” Calder added, drawing attention to a study observing a significantly weakened responses to the influenza vaccination in frail older people.
In addition, he explained that obesity is a significant cause of impaired immunity, due to reductions in the activities of T and B cells, reduced antibody responses, and heightened susceptibility to infection. A large-scale cohort study noted a significant association between overnutrition, as well as undernutrition, and hospital admission, ICU admission and mortality rates due to COVID-19.
“The most important message, which already existed but Covid exposed it, is that frailty and obesity both weaken immunity and increase risk and severity of infectious disease like COVID-19. We need to address both things to reduce the impact of future pandemics,” he stressed.
Nutrients and immunity
Calder added: “The other thing that Covid drew out is that there really are some magic bullets in our diet. Can we detect more of these to help us?”
He explained the importance of nutrition for immune health, providing fuel for energy generation, building blocks for essential immune cells such as amino acids for immunoglobulins, regulators for cellular responses including zinc and vitamin A, and protection from oxidative and inflammatory stress from vitamin C, E, and many phytochemicals.
In addition, he highlighted the importance of a diverse microbiota, supported through fibre and prebiotic consumption.
“We know that the fat-soluble vitamins A, D, E and probably K are very important for immunity. Also, the water-soluble B-vitamins and vitamin C are very important for immune support. Minerals, some amino acids, and several fatty acids are essential, and polyphenols may have a role,” he added.
Supplementation and COVID-19
Calder discussed specific supplemented nutrients which have been shown to be most effective in improving immunity, firstly spotlighting vitamin D due to its many roles within the immune system.
He explained: “The immune cells have vitamin D receptors, and more interestingly, can produce vitamin D. So, that tells us how important it must be for the immune system.”
Calder further highlighted that similar conclusions can be drawn for zinc and selenium supplementation, emphasising that low status has been associated with COVID-19 onset and more severe outcomes.
He added that a study noted that gut dysbiosis had been described in patients with Covid. He noted that the direction of the relationship had not been established but described a study investigating a probiotic treatment on Covid patients: “Probiotics, compared to the control, increased antibodies to the virus, increased viral load and lung infiltrates, and resulted in a shorter duration of both digestive and non-digestive symptoms.
“So, it’s possible that targeting the gut microbiota could be effective for COVID-19,” he concluded.