Supplementing above RDA may prove effective against respiratory infections
Writing in the journal Nutrients, the team use lessons learnt in the current crisis to favour this approach in tackling widespread incidences of inadequate nutrient intake leading decreases in infection resistance and an increase in disease burden.
“It should be noted that optimal nutritional support for the immune system can require intakes above the RDA for some micronutrients, while at the same time infections and other stressors can reduce micronutrient status in the body,” says the team led by Dr Philip Calder, professor of nutritional immunology at the university of Southampton.
“Vitamin C levels, in particular, decrease during times of infection and higher intakes are required to restore normal blood levels. These higher intakes and blood levels are associated with improved clinical outcomes.
“A daily intake of at least 200 mg/day for healthy individuals is recommended. This level is above the US RDA of 75 and 90 mg/day for female and male adults, respectively (EFSA recommend a vitamin C Average Requirement (AR) of 80mg/day for females and 90mg/day for males).”
Acute respiratory tract infections are a major cause of death worldwide as illustrated by both seasonal influenza epidemics, and the recent outbreak of the coronavirus disease caused by SARS-CoV-2 infection.
According to The World Health Organization (WHO) worldwide seasonal influenza alone results in around 3–5 million cases of severe illness that require hospitalisation, and 290,000–650,000 deaths annually.
Whilst vaccinations can prove effective in protecting against infectious disease, they can take years to create, are not available against all viruses (including the current coronavirus SARS-CoV-2) and provide varying levels of protection.
Micronutrients, minerals and omega-3
Against this background the team also recommend supplementation with the micronutrients vitamins A, B6, B12, C, D, E, and folate; trace elements, zinc, iron, selenium, magnesium, and copper; and omega-3 fatty acids is a safe, effective, and low-cost strategy to help support optimal immune function.
With the exceptions of vitamin E and magnesium, each of these micronutrients has been granted health claims in the European Union for contributing to the normal function of the immune system.
Other nutrients such as omega-3 fatty acids also support an effective immune system, specifically by helping to resolve the inflammatory response.
The team, which includes colleagues from the university of Otago, New Zealand, Oregon State University in the US and University Medical Center Groningen in The Netherlands, go on to suggest a series of mechanistic roles that micronutrients play to optimise immune function.
These include producing or having multiple effects on a single gene that supports immune function, specifically aiding the development and maintenance of physical barriers and production and activity of antimicrobial proteins
Other effects target the growth, differentiation and motility/chemotaxis of innate cells; phagocytic and killing (e.g., oxidative burst) activities of neutrophils and macrophages; and promotion of and recovery from inflammation (e.g., cytokine production and antioxidant activity).
Additionally, the team thinks an adequate omega-3 fatty acid (EPA and DHA) intake would support the resolution of inflammation via the production of anti-inflammatory metabolites of these fatty acids, including in the respiratory tract.
An intake of 250 mg EPA + DHA per day is recommended, say the researchers, consistent with global, regional and national expert recommendations.
“It is not surprising, then, that deficiencies and even suboptimal status of these nutrients can impair immune functions,” the team writes.
“Depending on the deficient nutrient or nutrients, there can be decreases in the numbers of lymphocytes, impairment of phagocytosis and microbial killing by innate immune cells, altered production of cytokines, reduced antibody responses, and even impairments in wound healing.
“These functional impairments are, presumably, what lead to the clinical immune-related manifestations of deficiency. Indeed, people deficient in vitamin C are susceptible to severe respiratory infections such as pneumonia.”
In the final of three recommendations, the research team also encourage public health officials to include nutritional strategies in their recommendations to improve public health.
Public health practices, such as vaccinations and hygiene measures, are important measures that help limit the spread and impact of infections, including against acute respiratory viruses.
However, the team states the present situation with SARS-CoV-2 infection and severe outcomes of COVID-19 and the annual morbidity and mortality figures for respiratory infections overall make it clear that these practices alone are not enough.
“New strains of influenza continuously emerge, necessitating development of new vaccines with varying efficacy, and outbreaks of novel viruses can be enormously difficult to contain,” they write.
“One compelling strategy [to support the immune system] is to provide sufficient nutritional support for the immune system.
“Optimal nutrient intake, including supplementing above the RDA for certain immune-supporting vitamins, promotes optimal immune function, helps to control the impact of infections, and could help limit the emergence of novel, more virulent strains of pathogenic viruses.
“We, therefore, strongly encourage public health officials to also include nutritional strategies in their arsenal to improve public health and to limit the impact of seasonal and emerging viral infections.”
Published online ahead of print: doi.org/10.3390/nu12041181
“Optimal Nutritional Status for a Well-Functioning Immune System Is an Important Factor to Protect against Viral Infections.”
Authors: Philip Calder, Anitra Carr, Adrian Gombart, Manfred Eggersdorfer