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Support Your Immune System to Protect Against Viral Infections

Diet and Supplements are Important Factors in Supporting Your Immune System to Protect Against Viral Infections

A recent article in Nutrients (Calder et al, 2020) outlined the importance of supplementation for key nutrients above the recommended daily limits, but below the upper tolerance limits, as an essential factor to help optimise the immune function to fight infection. This article aims to summarise some of the finer points. To read the full article, click here.


Vaccinations and good personal hygiene are important measures in limiting the spread of infections, however they are not sufficient. Supporting the immune system further protects individuals and is safe and cost-effective. Optimising the diet and supplementing above the recommended daily amount for key immune-supporting nutrients promotes optimal immune function, assists recovery, and helps limit the spread of disease.

Poor diets and increased need lead to inadequate intake of nutrients which are essential in supporting the immune system, leading to lowered resistance to infection. The immune system relies on a wide range of vitamins, minerals, and fatty acids to function effectively, and eating a nutrient-dense diet and supplementing a few key nutrients in higher dosages may be an effective strategy in improving individual, and therefore public health.

The Immune System

The immune system has two types of responses – innate (immediate, non-specific) and adaptive (slower, specific):

Innate Immunity

The innate immune system is our first line of defence. There are physical barriers, which include the skin and the mucous membranes of the gut and respiratory tract. If a pathogen breaches these barriers, the body will mount an inflammatory response to neutralise the invader it recognises as a non-specific foreign invader. Afterwards, the inflammation is resolved, and the body repairs the damage. The innate system does not ‘remember’ the pathogen and so does not learn to increase speed and efficacy in dealing with repeated attacks by the same pathogen.

Adaptive Immunity

The adaptive immunity provides a specific, tailored response to a pathogen. It is slower to respond, but it generates an immunological memory, and so future exposure to the same pathogen generates a fast and specific response. This is the mechanism which makes vaccinations effective.

Nutrition and Immunity

Both the innate and adaptive immune systems rely on vitamins and minerals, including vitamins A, B (several of the B’s), C, D, E, zinc, iron, selenium, magnesium, and copper. Other nutrients are needed to help resolve the inflammatory response once the attack is complete, including omega-3 fatty acids. Low levels of these nutrients can decrease resistance to infections and lengthen recovery time.

Vitamins C and D play an essential role in the immune system. Vitamin C supports the strength of the physical barriers of the first line of defence, the functioning of the cells needed in both the innate and adaptive immune systems, the movement of white blood cells to infection sites, the killing of the pathogens, and the development of antibodies. Vitamin C deficiency can lead to increased susceptibility to respiratory infections like pneumonia. Supplementation can decrease the risk of infection and reduce the duration and severity of upper respiratory tract infections.

Vitamin D has a key role in supporting all aspects of immunity, as there are vitamin D receptors on various immune cells including B cells, T cells, and antigen presenting cells, meaning these cell types rely on the presence of the vitamin to work effectively. Supplementation has been shown to reduce the risk of upper respiratory tract infections.

A key component of the immune response is inflammation, which then resolves once the pathogen is cleared, allowing for healing. Key nutrients involved in this resolution of inflammation include omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Unresolved inflammation is a factor in the pathogenesis of many diseases and can lead to the cytokine storm and acute respiratory distress syndrome (ARDS) implicated in COVID-19 and other infections. EPA and DHA are essential in avoiding long-term lung injury.

Ideally sufficient levels of these nutrients would be achieved through a healthy diet, but that can be difficult to achieve at the levels needed to strengthen the immune system in times of increased need. Supplementation is an effective way to support the immune function and fill in nutritional gaps, reducing the risk of infection.

Conclusion and Recommendations

Calder et. al recommend the intake of key nutrients above the recommended daily amounts, but within the upper safety limits. Taking a multivitamin in addition to eating a balanced and healthy diet is recommended, as well as supplementing the key nutrients discussed above.

The authors recommend Vitamin C supplementation of at least 200mg/day daily for healthy individuals, and even more with those with increased needs. The tolerable upper limit (in the US) for adults is 2g/day, and 400mg/day in children 1-3 years old. 1-2g/day daily is recommenced for adults who are sick, at the onset of symptoms.

Daily or weekly vitamin D supplementation effectively reduces the risk of upper respiratory tract infections, and so the authors recommend 2000IU (50ug) per day. The tolerable upper limit is 2500-4000 IU over 1 year of age.

For effective resolution of inflammation, the authors support an intake of 250mg EPA+DHA daily.

A balanced, nutritious diet which includes supplementing above recommended levels for certain nutrients helps to promote optimal immune function, decreases the risk of infections, promotes the resolution of infection, and can help decrease the spread of disease.


The nutritional therapists at Julia Davies Nutrition do not recommend self-prescribing supplements. Everyone has unique, individual needs, and we strongly recommend contacting us for an appointment to discuss optimising your health and immune system with a review of your diet, health concerns, current medications, and supplementation.

Written by: Alissa Powell

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