What can you eat to support your immune system this winter?

Article by Marie Donnellan ANutr

What can you eat to support your immune system this winter?

As we come into the winter season, people start to look at ways to “boost” their immune system to guard against colds and flus! The idea that you can boost your immune system is tempting but the immune system is a complex system and there is no single food group or means that can boost your immunity! Whereas nutritious food and a healthy lifestyle are some of the best ways of supporting your immune system to function and keep you healthy, because a poorer diet can result in a weakened immune response (1).

No one food choice is to blame for poor health, in the same way that no single food choice is responsible for good health either!

We have previously written about immune fitness, what is it and what can you do to achieve it especially from a workplace perspective. To learn more, you can read What is Immune Fitness and what employers can do to support it?

What is the best dietary approach?

So, what is the best dietary approach to support the normal functioning of our immune system?

The Mediterranean diet is one that is primarily plant-based eating, which includes daily intake of whole grains, olive oil, fruits, vegetables, legumes, nuts, herbs, and spices. Animal proteins are eaten in smaller quantities and those preferred are fish and seafood with limited red and processed meat (2).  This diet contains lots of antioxidant and anti-inflammatory properties, these may help support our immune system’s healthy functioning. (3)

Plus eating a varied diet that contains enough nutrients is vital for the health and function of all cells of the immune system. Therefore, no one individual food choice offers greater protection, it’s the overall intake and the variety of micronutrients in a balanced healthy diet, that supports the best function of the immune system.

Key nutrients to support our immune system?

A diet that is limited in variety and lower in nutrients, can negatively affect the health of our immune system. This is because a poorer nutrient status has been associated with inflammation, and oxidative stress both of which negatively affect our immune system (4).

When we have a varied diet and regularly eat food that contains the vitamins and minerals below, we will support the normal functioning of our immune system.

• Vitamin A – is anti-inflammatory and supports immune cell production. It’s found in leafy green vegetables (kale, spinach, broccoli), orange and yellow vegetables (carrots, sweet potatoes, pumpkin and other squash), tomatoes, red peppers, cantaloupe, mango and beef, liver and milk as well as some fortified foods (5).
• Vitamin C – there isn’t robust evidence that it prevents you catching a cold, however it’s an antioxidant found in fruit and vegetables like peppers, kiwis, oranges and broccoli.
• Vitamin D – deficiency has been linked with a reduced immune response. It is found in oily fish such as salmon, sardines, trout, herring, egg yolk, offal and fortified foods like breakfast cereals, milk and yoghurts (6, 7).
• Iron – important for immune function and response. It is found in red meats (beef, lamb and pork) and offal are particularly rich sources of iron which is easily absorbed. Plant-based sources include pulses and legumes (such as beans, peas, and lentils), dark green vegetables (such as spinach, kale and broccoli) and nuts and seeds. (8,9)
• Zinc – aids the production of immune cells and is found in shellfish, red meat, eggs, nuts, seeds, lentils, chickpeas and whole grains.

As always, it’s about balance. When we eat a variety of foods these will provide the adequate amounts of the nutrients, required to support our immune function.
Just to also note, it can be difficult to obtain enough vitamin D in Ireland. Due to the lack of sunshine and intake from foods. Consequently, it’s good practice to take a vitamin D supplement daily during the autumn and winter months from around October to March, to help ensure that you have adequate levels.

The importance of the gut and our immune system

We now understand that our gut microbiome is pivotal in our health and one of its key functions is in regulating our immune system. Research now shows that between 70 and 80% of our immune system, resides in our gastrointestinal tract. The gut microbiome stimulates the intestinal immune cells, so the composition and health of this environment is important (10).

One of the best ways that we can support our gut health, is by increasing our fibre intake.

Aiming for between 25- 30g of fibre every day. The best way to achieve this is by eating a variety of fruits and vegetables, wholegrains (pasta, rice and bread) and by increasing other plant-based foods like beans and legumes, nuts, and seeds.

“Between 70%-80% of our immune system is located in our gut”(10)

There is always confusion around which prebiotic foods and probiotic foods best support gut health. Prebiotic foods are those that support beneficial bacteria growth like onions, leeks, shallots, garlic, banana, artichokes, oats, apples and asparagus and probiotic foods may contain beneficial live bacteria like natural yoghurt, kefir, kimchi, sauerkraut can help support the development of a healthy gut microbiome and therefore a healthy immune system.

Lifestyle factors can also play a part!

Besides what we eat, there are several lifestyle factors that can support the healthy functioning of our immune system, such as (11):

• Getting enough sleep
• Being physically active
• Managing stress levels
• Avoiding excess intake of alcohol
• Not smoking

One of best defences we have is to follow a healthy diet and lifestyle. By doing this we are taking the best approach towards naturally keeping our immune system working properly. Every part of our body, including your immune system, functions better when it has the nutrients to support optimal functioning to protect us every day.

References

1. Childs, Calder and Miles, 2019. Diet and Immune Function. Nutrients, 11(8).
2. The Nutrition Source. 2022. Diet Review: Mediterranean Diet.
3. Casas, R., Sacanella, E. and Estruch, R., 2014. The Immune Protective Effect of the Mediterranean Diet against Chronic Low-grade Inflammatory Diseases. Endocrine, Metabolic and Immune Disorders-Drug Targets, 14(4).
4. Iddir, M., et al., 2020. Strengthening the Immune System and Reducing Inflammation and Oxidative Stress through Diet and Nutrition: Considerations during the COVID-19 Crisis. Nutrients, 12(6).
5. Gürbüz, M. and Aktaç, Ş., 2022. Understanding the role of vitamin A and its precursors in the immune system. Nutrition Clinique et Métabolisme, 36(2).
6. Aranow, C., 2011. Vitamin D and the Immune System. Journal of Investigative Medicine, 59(6).
7. BDS.uk.com. 2022. Vitamin D
8. Cherayil, B., 2010. Iron and Immunity: Immunological Consequences of Iron Deficiency and Overload. Archivum Immunologiae et Therapiae Experimentalis, 58(6).
9. BDA.uk.com. 2022. Iron.
10. Wiertsema, S., et al., 2021. The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies. Nutrients, 13(3).
11. CDC., 2021. [online] Available at: <https://www.cdc.gov/nccdphp/dnpao/features/enhance-immunity/index.html>