The immune system is a complex network of organs, cells, proteins and tissues which all work together to protect the body from foreign invaders and disease.
The immune system is made up of two parts; the innate immune system, which we are born with, and the adaptive (or acquired) immune system, which is built over time from exposure to the environment.
The immune system is strongly influenced by nutrients. The following vitamins, minerals and specific foods are important to prioritise in the diet for optimum immunity and overall health.
Vitamin D
Vitamin D is vital for the immune system, it modulates both the adaptive and innate immune responses. Vitamin D deficiency has been associated with a greater risk of autoimmunity as well as an increased susceptibility to infection.
Vitamin D deficiency occurs with less than 30 nmol/L (nonomoles per litre).
In a study, individuals with lower vitamin D levels than this were more likely to self-report a recent upper respiratory tract infection than those with sufficient levels, even after adjusting for variables including season, age, gender, body mass and race.
Exposing your bare skin to sunlight is the best and most effective way to create vitamin D in the body.
However, if you live in the Northern Hemisphere, vitamin D deficiency is common due to the lack of sunlight during the winter months, so a supplement is usually required.
In food, vitamin D is found in fatty fish such as tuna, mackerel and salmon, and fortified foods such as orange juice and fortified cereals. Mushrooms are also a good source of vitamin D when they have been exposed to sunlight.
The NHS recommends all people in the UK take a vitamin D supplement of 10 micrograms per day minimum during the winter months. The most absorbable type of Vitamin D is Cholecalciferol (D3).
Vitamin A
Vitamin A is important for immune function, reproduction, vision and cell metabolism. It’s a powerful antioxidant which has been shown to provide enhanced defence against numerous infectious diseases.
Two forms of Vitamin A are found in the diet; retinol and beta-carotene.
Retinol is found in animal products such as meat (particularly liver) fish and dairy.
Beta-carotene is found in plants and fruits, especially carrots and colourful vegetables such as sweet potato, bell peppers, mango and dark leafy greens such as kale, spinach and broccoli.
Vitamin C
Many cells of the immune system need vitamin C to function. Vitamin C isn’t made or stored in the body so it must be included in your diet every day. Vitamin C is found in many fruits and vegetables, especially peppers, broccoli, kale, sweet potatoes, kiwi, citrus fruits, strawberries and cantaloupe melon.
During times of acute illness or stress, a Vitamin C supplement can be helpful to support the immune system.
Vitamin E
Vitamin E is a powerful antioxidant which plays an important role in immune function, for example research has shown its ability to reduce respiratory infections in the elderly.
Many foods contain this important antioxidant including nuts, seeds, plant-based oils, fish and leafy greens. Vitamin E deficiency in Western countries is uncommon, therefore supplementation isn’t usually necessary.
Vitamin E is stored in the liver before being released into the bloodstream.
B Vitamins
B Vitamins are water-soluble vitamins that play an important role in cell metabolism and immune response.
Each B vitamin has a special function and while most can be obtained through a healthy, varied diet, supplementation can sometimes be needed, such as for those following a vegan diet.
Top sources of B vitamins include meat (especially liver), seafood, poultry, eggs, dairy products, legumes, leafy greens, seeds, and fortified foods, such as breakfast cereal, milk and nutritional yeast.
Zinc
Zinc is a trace element required by the immune system to function effectively. Even a mild zinc deficiency can increase susceptibility to infections, therefore adequate dietary zinc should be emphasised to protect the immune system.
Oysters contain more zinc per serving than any other food but zinc is also found in whole grains, nuts, seeds, legumes and meat.
Many vitamin C supplements actually include zinc if you choose to supplement.
Selenium
Selenium is an essential mineral and a powerful antioxidant which is vital for many aspects of the immune system.
Low dietary intakes of selenium can be associated with a wide range of diseases, so it’s important to emphasise this vital mineral in the diet.
Brazil nuts are an excellent source of selenium but as it can be difficult to know precisely how much an individual nut can contain, you probably don’t want to eat a whole bag at once! Around five nuts per day is ideal.
Sardines are another great source of selenium and contain other essential nutrients including omega-3 fatty acids and vitamin B12.
Additional foods containing selenium are eggs, beef and oats.
Our immune system is perfectly designed to adapt and protect us from countless insults every day. But just like any other organ in the body, it needs nourishment to function at its best.
Consistently adding these foods into the diet will help it function as it was designed.