What is The Immune System?
The immune system is a network of processes in the body that protects us from disease. It detects and defends our body against threats like, viruses, bacteria, and foreign bodies, by differentiating our tissue from foreign tissue. A number of cells and organs work together to protect our body, such as the lymphatic system, the spleen, white blood cells, antibodies and bone marrow.
White blood cells have a key role in the immune system and can be split into two types, known as phagocytes and lymphocytes. Phagocytes are used to “eat” foreign cells as they engulf and digest any foreign particles detected in the body. Lymphocytes are used to help the body remember past invaders to make the immune response quicker. Two types of lymphocytes are B cells and T cells. B cells create antibodies to be used to destroy foreign bodies. T cells are used in the destruction of any cells in the body that have been taken over by viruses or have become cancerous.
The Immune Response
The immune response is triggered when foreign substances are detected in the body. This can occur when a phagocyte or an infected cell in the body presents an antigen on its surface. Antigens are any foreign substance that triggers an immune response. Once these particles have been detected by the body B cells create antibodies, which are used to lock onto the antigens. Then, the T cells destroy the antigens that have been marked by antibodies. After the immune response, antibodies tend to stay in our system. This means that if our body faces the same threat again, the antibodies are already there to fight it off.
The Effect of Diet on the Immune System
Nutrition plays an important part in supporting immune function and poor nutrition can lead to a compromised immune system .
Meeting your five-a-day is one way to support your immune system. Fruit and vegetables contain micronutrients such as vitamins and minerals, as well as phytochemicals and antioxidants. Antioxidants are substances in foods that help to neutralise free radicals in the body. Free radicals are unstable atoms that cause damage to cells, which can lead to illness and cancer.
Antioxidants can be found in foods high in micronutrients, like vitamin A, vitamin C, vitamin E and selenium. Phytochemicals are what gives fruit and vegetables their colour. Some research has shown that they can play a similar role to antioxidants and help to prevent the formation and attack of carcinogens in the body. Phytochemicals can be found in fruits and vegetables high in micronutrients, such as carotenoids, flavonoids, indoles and isoflavones. You can read more about meeting your five-a-day on our previous 5-a-day blog.
There are a number of vitamins and minerals that have been found to support immune function.
Vitamin C can be found in foods such as:
It is recommended that adults between 19 and 64 years of age should consume around 40mg every day . In terms of the immune system, vitamin C has been found to support immune function in many ways. Firstly, vitamin C is an antioxidant, which can help to protect cells against free radical damage. Additionally, it helps to stimulate the production of phagocytes and lymphocytes, key components in the immune response. Vitamin C also promotes good skin health and, in some cases, faster wound healing . This may prevent foreign substances from entering the body through the skin.
Vitamin D is synthesised from sunlight on your skin when you go outside. It can also be found in foods like oily fish, egg yolks, mushrooms, and fortified food products. Low levels of vitamin D have been found to be associated with a reduced immune response .
Vitamin D has been found to enhance the function of cells involved in the immune response, including T cells. It has also been found to benefit the function of cells known as macrophages, a type of phagocytes, used to engulf bacteria and cause inflammation at the area of damage. Inflammation helps to alert other cells in the immune system to respond to this area of the body. However, too much inflammation can cause inflammatory diseases or excess cellular and tissue damage, therefore vitamin D’s anti-inflammatory properties can be useful to prevent excessive inflammation from happening .
Zinc is a mineral found in whole grains, chickpeas, nuts, and meat. The recommended amount of zinc needed by adult men is 9.5mg and 7mg for adult women .
Zinc has been found to support the immune system by activating enzymes that break down proteins in viruses and bacteria. This helps to prevent the spread of these substances through the body. Furthermore, it increases the activation of macrophages, neutrophils, another type of white blood cell that helps to heal tissue and address infections, and NK cells, a type of lymphocyte, to fight infection. Similarly to vitamin C, it also promotes wound healing, to prevent foreign bodies from entering the body through wounds and causing infection.
Whilst zinc, vitamin C and vitamin D help to support the immune system, it is important to note that there isn’t an individual nutrient that can “boost” the immune system. Multivitamins are often advertised as a way to meet our micronutrient needs but a healthy and balanced diet is recommended over these supplements to support your immune system. Consuming multivitamins may lead to overconsumption of micronutrients, which can have negative side effects. Some micronutrients, such as vitamin D, may benefit from supplementation. During spring and summer, the body should be able to create enough vitamin D from sunlight but during darker months it may be beneficial to supplement with around 10 micrograms of vitamin D a day. However, it is important to consult with a medical professional before beginning to take supplements.
Top Tips for Supporting the Immune System
- Meet your 5-a-day to increase your intake of antioxidants and phytochemicals.
- Eat foods high in zinc to increase the activation of cells within your immune system.
- Eat foods containing vitamin C to promote good skin health and increase the production of phagocytes and lymphocytes.
- Eat foods containing vitamin D for its anti-inflammatory effects and enhanced function of cells involved in the immune response.
- Eat a healthy, balanced diet to meet all of your micronutrient needs rather than reaching for unnecessary supplements.
Written by Libby Grimshaw (nutrition intern) and reviewed by Caroline Hill (Dietitian)