The immune system is a complex network of cells, tissues, and organs in the body that work together to keep us healthy and protect us against infections and diseases. When our immune system isn’t functioning properly, we are more vulnerable to picking up viruses and any other ‘bugs’ that are going around. This is why it’s important to strengthen your immune system.
There are no ‘superfoods’ or supplements that can ‘boost’ the immune system, so alarm bells should ring when these kinds of claims are being made. Also, we don’t actually want to boost the immune system, as an over-active immune system can cause as many problems as one that is under-functioning.
Having said this, a healthy diet does play an essential role in supporting and strengthening the proper functioning of our immune systems. In fact, more than 20 different nutrients are necessary for it to function efficiently. Through a healthy balanced diet, we can ensure the immune system is working at its best and is able to do its job of protecting us.
1. Balanced and Varied Diet
The foundation for a healthy immune system (and health in general) is a balanced and varied diet. This means a diet based on whole, unprocessed foods with the vast majority of your food coming from plants.
Fruits, vegetables, pulses, wholegrains, nuts and seeds should be eaten in plentiful amounts, forming the bulk of the diet with small amounts of good quality animal foods, such as dairy and fish if you choose to include them.
This will provide the range of different vitamins, minerals, antioxidants and other nutrients required by the body as a whole and the immune system. The fibre from plant foods is also important for keeping the gut healthy, including maintaining a healthy microbiome (see number 3 below).
This is how a typical day on a high-fibre, plant-based diet might look:
Breakfast: Bircher muesli with berries, nuts, seeds and dried fruits
Lunch: rye bread sandwich with hummus, watercress and grated carrot
Dinner: spiced lentil daal with brown rice and broccoli
Snacks: fruit, nuts and oatcakes
2. Vitamin C
Vitamin C is involved in several aspects of immunity. Firstly, it has been shown to increase the levels of substances called interferons in the body. Interferons are a group of proteins produced by white blood cells, involved in the body’s defence against viruses and other harmful pathogens.
Vitamin C also has antioxidant and anti-inflammatory actions – both of which are beneficial to overall health and immunity. Inflammation is in fact, one cause of the unpleasant symptoms during viral infections, such as aches and pains. Finally, vitamin C is essential for collagen synthesis in the body which gives structure to tissues including the skin, gut and respiratory tract that form a physical barrier to harmful organisms entering the body.
The best way to ensure adequate vitamin C intake is to eat plenty of different fruits and vegetables every day; include 7 or more servings ideally if you can. The richest sources are peppers, citrus fruits, kale, spinach, broccoli, berries, tomatoes, peas, blackcurrants, kiwi, guava and papaya, so be sure to include some of these.
3. Look after your Microbiome
The trillions of bacteria located in our gut, known as the microbiome, influence many aspects of health including our immunity. The microbiome communicates with the immune system, helping it to respond effectively to threats and a healthy microbiome is crucial for protecting us against harmful pathogens, including viruses. The microbiome has many roles in immunity, many of which are still being revealed. For example, regulating inflammation, producing many beneficial chemicals and activating vitamin A (see below).
Increasing the numbers and diversity of ‘good’ bacteria in the gut can strengthen our body’s defences. There are two ways of doing this; firstly, we can eat foods that contain the beneficial bacteria themselves, known as probiotics. Natural live yoghurt, artisan cheeses and fermented foods such as sauerkraut, kimchi, kefir and kombucha all contain probiotics. Secondly, we can consume foods that feed the gut bacteria and encourage them to multiply, known as prebiotics. These are found in plant foods, and the best way to get plenty is to eat a varied, high-fibre plant-based diet
Beta-carotene is converted in the body to Vitamin A, which is an essential nutrient for immune system function. Vitamin A is necessary for the production of a type of white blood cells called T-lymphocytes, which help the body identify dangerous cells such as viruses. Vitamin A deficiency is well known to lead to impaired ability to fight off infectious diseases.
Beta-carotene (and other carotenoids) has also been shown in studies to have effects that appear to be separate from its role as a precursor to vitamin A. These include increasing the numbers and activity of various immune cells, such as increasing white blood cell count and enhancing the activity of natural killer cells, which kill virally infected cells.
The richest food sources of beta-carotene are orange, yellow and dark green fruits and vegetables, such as sweet potatoes, carrots, spinach, kale, butternut squash, peppers, cantaloupe melon, apricots and mango.
5. Vitamin D
Vitamin D deficiency is associated with an impaired immune response. Our main source is sunlight, which accounts for approximately 90% of our total vitamin D, with the remaining 10% coming from dietary sources.
From October to March, it is difficult to obtain enough vitamin D, due to the lack of sunshine, so supplementation is recommended. Being indoors during self-isolation could increase this need for a supplement and the NHS are advising everyone on lockdown to take one.
There is even some preliminary research being carried out in Ireland, suggesting that countries with more sunshine, such as Australia, may have lower mortality rates from COVID-19, due to higher vitamin D levels.
For this reason, it is advisable to take the following three measures to maximise your vitamin D status and strengthen your immune system:
1) take a vitamin D supplement
2) take your daily exercise outside whenever safe and possible to do so, keeping some skin exposed and
3) include dietary sources of vitamin D; oily fish, eggs and some fortified foods.