Thoughts from our High-Value Nutrition Chief Scientist, Professor Richard Mithen

Our last HVN newsletter was on 16 December 2019. It was about the time that the first case of a new coronavirus was identified in Wuhan. How the world has changed…

One of the questions I am regularly asked is whether certain foods can ‘boost the immune system’, and this is particularly relevant during the present Covid-19 pandemic. Unfortunately, there is not a simple answer to this straightforward question. The human immune system is a complex affair. It can be divided into two major parts – the ‘innate’ immune system, and the ‘adaptive’ immune system. These two parts of the immune system work together, often with the innate system mounting an early response to infection, which is then complemented by the more effective adaptive immune system.

The innate system is a generalised response to pathogens or other substances that our bodies recognise as ‘foreign’. It is typified by an ‘acute inflammatory response’ that includes the release of a complex series of compounds. Among the compounds released are eicosanoids, which may cause blood vessel dilation and an increase in cell temperature at the site of infection, and cytokines that have a range of complex effects including the attraction of immune cells to the site of infection, the suppression of virus replication and cell healing.

Sometimes the innate immune system can misfunction. Many forms of allergy can be thought of as being due to an inappropriate innate immune response to proteins in certain foods, such as those in milk products and certain fruits, nuts, pollen, and insect stings.

The development of the immune system in infancy is critical to be able to mount an appropriate immune response and to prevent these allergic responses. There is much research worldwide seeking to understand how early exposure of babies and infants to potential allergens may help them develop a functional immune system.

Some of these issues are being addressed in the High-Value Nutrition National Science Challenge through the research by Professor Clare Wall at the University of Auckland, and Dr Olivier Gasser at the Malaghan Institute of Medical Research, who are investigating how exposure to certain foods at weaning may help infants develop a robust immune system. The innate immune system may also misfunction to produce a more systemic ‘chronic’ inflammatory response, as opposed to the short sharp acute response.

Chronic inflammation is characterised by the appearance of a long-term stimulation of cytokine and eicosanoid release, which can damage organs. This can predispose the human body to diabetes, cardiovascular disease and cancer. Chronic inflammation is often associated with obesity, but we are not sure if one causes the other.

Diets rich in omega-3 ‘fish oils’, such as those found in green-lipped mussels and oily fish, can suppress chronic inflammation and this is being investigated by HVN-supported research by Dr Matt Miller at the Cawthron Institute, and Professor Marlena Kruger and her colleagues at Massey University. Lastly, the innate system can misfunction and cause a ‘cytokine storm’, in which a massive overproduction of cytokines can lead to multiple organ failure. This is seen in some patients with Covid-19.

The ‘adaptive’ immune system is a system that mounts an attack to a specific pathogen, which the immune system has learnt to identify from previous exposure. ‘B’ cells and ‘T’ cells are produced from the bone marrow and mount specific attacks against invading pathogens that they have learnt to recognise. This ‘memory’ occurs via cells that recognise proteins on the outside of a particular pathogen from a previous encounter so that if the pathogen attacks again, the body can mount a swift response. This is, of course, the basis for vaccination, in which either an ‘attenuated’ virus (i.e., one with parts of the genome removed and thus not dangerous) or an isolated protein from the virus coat is introduced to train our cells to recognise the virus when it attacks.

Coronaviruses such as Covid-19 have protein spikes on their outside and these are currently being used to develop vaccines in many laboratories. ‘T’ cells kill our own cells if they have become infected with viruses and require vitamin D to be effective. This is one reason why it is important to maintain our vitamin D levels through appropriate exposure to sunlight and eating a diet rich in oily fish. Indeed, this is one of a few established connections between our diet and a functioning adaptive immune system. It is also likely that a number of trace elements in our diet such as zinc, selenium and copper, which may often be deficient in economically-developed societies such as in New Zealand, may be important for the functioning of our immune system.

We have much to learn about the links between our diet and how it may improve our immune system. A poor diet can lead to chronic inflammation and obesity, which are risk factors for diabetes, heart disease and cancer. We need to understand how certain foods may be able to suppress chronic inflammation, while enabling and enhancing an acute immune and inflammatory response at the sites of an infection.

New Zealand is well equipped to tackle this challenge. Dr Olivier Gasser leads the HVN Immune Health research programme at the world-leading Malaghan Institute of Medical Research in Wellington,collaborating with nutrition and biomedical scientists from across New Zealand, and with the commercial food sector. This programme is seeking to unravel many of the complexities of the relationship between our diet and our immune system.

It is unlikely that we will find a dietary ‘magic bullet’ to boost our immune system to protect us against emerging pathogens such as Covid-19. It is, however, without doubt that a healthy diet can lead to the prevention of chronic diseases such as Type II diabetes and hypertension, probably by the suppression of an inappropriate chronic immune response. This in turn will help our bodies fight off these new infections when they strike, as undoubtably they will…again and again.