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Does what we eat help us fight the coronavirus disease?

Getting enough of the right nutrients means you're better equipped to combat disease.

It’s debatable whether Hippocrates really said, “Let food be thy medicine”, but what’s not under debate is the evidence that a nutritious diet will support our immune system. And although there are no guarantees we can avoid Covid-19 altogether, there’s no better time to seriously consider the effect of what you eat on your health.

Across the globe there have been widely varying rates of illness and death in different countries as a result of Covid-19. It’s been hypothesised that France’s higher smoking rate may partially explain that country’s higher-than-expected illness rates, for example. Certainly considering the environment, demographics and nature of the virus itself are crucial. But are the lifestyle and diet of individuals within each population also appreciably affecting their risk?

A typical Western diet is energy-dense and rich in refined sugars, salt, white flour, processed meats, purified animal fats and food additives, with low amounts of fibre, vitamins, minerals and other plant-derived molecules such as antioxidants.

In addition to being low in important micronutrients, a typical Western diet also triggers inflammatory responses both directly and indirectly via alterations in the gut microbiome, says a review published in the journal Immunity late last year. It’s this type of chronic inflammation that has been linked to an increased risk of a number of serious conditions, such as Alzheimer’s disease, cancer, heart disease and diabetes.

Interestingly, Covid-19 is a disease that is characterised by an “overexuberant inflammatory response”. Whether this dietary-influenced inflammation would worsen outcomes for virus-afflicted patients is unknown, but a 2014 review concluded that Western-style diets reduced the ability to control infections.

In contrast, traditional diets with more wholefoods and unprocessed ingredients can reduce inflammation and optimise our immune system. The Mediterranean diet, for example, is based on the consumption of high amounts of vegetables, fruits, cereals, legumes, nuts, fish and the use of olive oil. Several human trials have shown that a Mediterranean dietary pattern is associated with reduced metabolic and cardiovascular risk and lower levels of inflammation.

A number of important micronutrients found in these types of wholefoods can also help our immune system to operate at an optimum level. These include vitamins A, C, D, E, B2, B6, and B12 and folic acid, along with the minerals iron, selenium and zinc, noted a 2018 review published by the journal Nutrients (a review conducted by Bayer HealthCare staff). When we have optimal levels of these micronutrients, resistance to infection is increased and this supports a faster recovery if we do become infected.

All these micronutrients play differing but important roles in both our innate immune system and our adaptive immune system. The former is the non-specific part of our immune system that defends us against anything foreign (this includes our skin, for example). Our adaptive (acquired) immune system is highly specific and identifies pathogens.

Vitamin A is found in the form of provitamin A (which our body can convert into vitamin A) in many vegetables. The richest sources are green leafy vegetables, along with orange and yellow vegetables (for example, carrots, kumara, pumpkin, squash) and certain fruits such as mangoes and oranges. Preformed vitamin A is also found in foods of animal origin such as milk, cheese, fish and liver.

Vitamin C is found in fruits and vegetables, and although citrus fruit are often heralded as the richest of sources, SunGold kiwifruit contain almost twice as much vitamin C (130mg per fruit) as an orange (72mg) that is twice the size. Along with kiwifruit and citrus, red and green capsicums, broccoli, strawberries, brussels sprouts and rock melon are also rich sources.

Vitamin D is produced in our body through sun exposure, but during winter this can be difficult, which is why the Ministry of Health recommends vitamin D supplements for certain population groups. Vitamin D is also found in eggs, fish and some fortified milks and margarine brands.

Vitamin E is found in nuts, seeds, green leafy vegetables and vegetable oils. And if you include two brazil nuts in your daily handful of nuts, you’ll also meet your selenium requirements (a mineral deficient in New Zealand’s soils and therefore our food supply), another important micronutrient required for our immune system.

Water-soluble vitamin B2, also known as riboflavin, is found in high amounts in eggs, offal, lean meats, milk and milk products. Note that plant-derived milks do not naturally contain vitamin B2, though some manufacturers add it to their products. Check the ingredients list to confirm if your plant-derived milk contains vitamin B2.

Vitamin B6 is found widely distributed in our food supply in meats, breakfast cereals, wholegrains, fruits and vegetables.

Folate or vitamin B9 is found only in small amounts in many foods. Good sources include green leafy vegetables such as broccoli, brussels sprouts, cabbage and spinach, along with liver, peas, legumes and fortified breakfast cereals.

Vitamin B12 is found only in foods of animal origin, including meat, dairy products and seafood. Vegans are therefore at risk of vitamin B12 deficiency and should supplement their diet. Those who avoid many animal-derived foods and drinks should also be aware that their vitamin B12 level may be affected.

Iron in food can come in either haem or non-haem forms. Meats, fish and poultry contain haem iron, which is easily absorbed by our body. Non-haem iron is found in wholegrain cereals, nuts and other plant-derived foods. The haem form is more easily absorbed and used by our bodies.

Zinc is widely distributed in our food supply, with meat, fish and poultry major contributors to our intake, though cereals and dairy foods also provide appreciable amounts.

This article appears in the upcoming issue of the Listener, which is on sale Monday, but we are releasing timely stories early.

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