What is Your Immune System and How Does it Work?
- to fight disease-causing germs (pathogens) like bacteria, viruses, parasites or fungi, and to remove them from the body,
- to recognize and neutralize harmful substances from the environment, and
- to fight disease-causing changes in the body, such as cancer cells.
When your immune system is running smoothly and doing its job, you don’t notice that it’s there because you feel fine. But if it becomes weak or can't fight particularly aggressive germs – you can become ill. Germs that your body has never encountered before are also likely to make you ill until your immune system can create antibodies to fight them. That's why some germs will only make you sick the first time you come into contact with them, such as childhood diseases like chickenpox.
Basically, there are two small subsystems that make up your immune system. These are scientifically known as the innate (non-specific) immune system and the adaptive (specific) immune system (2). Both of these subsystems are closely connected to one another, and work together whenever a germ or harmful substance triggers an immune response.
The innate immune system works as a defense against harmful germs and substances that enter the body through the skin or digestive system. It uses immune cells such as natural killer cells and phagocytes (“eating cells”) to fight pathogens in our bodies.
The adaptive (specific) immune system is the part that actually makes antibodies and uses them to specifically target and fight certain germs that the body has previously come into contact with. This is an “acquired” (learned) or specific immune response. The adaptive immune system is constantly learning and adapting so that the body can fight bacteria or viruses that change over time.
How We Get Sick
Today, we know that there are two major kinds of diseases: non-infectious and infectious. Non-infectious diseases aren't caused by pathogens and can't be spread person-to-person. These diseases are more likely to be caused by a variety of factors including the environment, a person's lifestyle choices, and genetics. For example, skin cancer is usually the result of people spending too much time in the sun without protection from the sun's UV rays, which is considered an environmental factor. A condition like heart disease may be caused by a sedentary lifestyle and a poor diet, or it may be caused by a family history of the disease. (4)
Infectious diseases, on the other hand, are caused by pathogens such as bacteria, viruses, fungi and parasites, which can enter the body through the air we breathe, the food we eat and drink, or through openings in the skin, such as cuts. For example, a person who has a cold may cough into their hand and then touch a doorknob, placing the cold virus on that doorknob. The virus may die on the doorknob, but it's also possible that the next person to touch the doorknob will pick it up. If that person then touches food with the unwashed hand and consumes the food, the virus is now inside the body.
Not every germ that enters the body results in illness. Have you ever noticed that some people are always getting sick while others rarely get sick? That’s because people that have a strong immune system have a better chance of fighting off sickness, while those who have weakened or compromised immune systems will find it harder to fight off an invading pathogen.
The good news is that there are plenty of things that we can do to prevent illness. A proactive approach would include adopting healthy lifestyle choices, avoiding risk factors, and choosing to eat healthy foods that contain key nutrients to strengthen and support our immune system.
7 Key Nutrients that Support Our Immune System
1. Vitamin A
Vitamin A is a powerful anti-oxidant with a critical role in enhancing immune function. This micronutrient is involved in cellular immune response and provides enhanced defense against multiple infectious diseases.(4)
Vitamin A is found in bright orange and yellow foods like sweet potato, mango, carrots, bell peppers, and dark leafy greens like kale, spinach, and broccoli.
2. Vitamin C
Vitamin C is probably the most well-known anti-oxidant, and thousands of people take high-dose supplements with hopes of "boosting" their immune system. However, research shows that vitamin C from food at a dose of 100 mg to 200 mg per day is effective at preventing respiratory infections.(5)
You can get vitamin C from whole food sources like citrus fruit, cabbage, strawberries, cauliflower, red bell peppers, garlic, mushrooms, and mango.
3. Vitamin D
It is now clear that vitamin D has an important role in supporting the immune system. Research has demonstrated that Vitamin D can modulate the innate and adaptive immune responses. Deficiency in vitamin D is associated with increased autoimmunity as well as an increased susceptibility to infection.
Vitamin D is often taken in supplemental forms, but can also be obtained from responsible sun exposure and foods such as fatty fish, beef liver, egg yolks, cheese, and mushrooms.
4. Vitamin E
Vitamin E plays an important role in immune function and supplementation has even been shown to reduce respiratory infection in the elderly.(4) Most typical diets do not provide adequate vitamin E, but symptoms of a deficiency can be so subtle that individuals may not know if they are deficient.(6)
Rather than relying on supplements, deficiency can be prevented through adequate dietary intake of foods like nuts, seeds, leafy greens, and healthy, plant-based oils as a way to keep the immune system functioning optimally. One reason for a significant decline in cellular immunity associated with aging could be due to inadequate intake of anti-oxidants like vitamin E. Diets high in vitamin E naturally improve immune function, even without supplementation.(7)
Selenium is an essential mineral that acts as a powerful anti-oxidant. Adequate dietary selenium is required for the function of almost every aspect of the immune system and deficiency can have serious consequences when it comes to fighting infections.(8)
Brazil nuts are extremely high in selenium, but can easily exceed the daily required limit and can even cause toxicity if eaten frequently. Two Brazil nuts a day can easily satisfy your daily requirement. Sardines are also an excellent source of selenium that can be eaten more frequently (if you can handle the taste) and provide anti-inflammatory omega-3 fats which also have beneficial effects on the immune system. Pork, beef, turkey, chicken, fish, shellfish, garlic, mushrooms, dairy, and eggs also contain high amounts of selenium.
Like selenium, zinc is an essential mineral critical for immune function. Even mild to moderate zinc deficiency can weaken your immune function and increase the risk of respiratory infections. Adequate dietary zinc should be a priority for anyone looking to protect their immune system.(9)
Zinc is found in nuts, seeds, dairy, eggs, shellfish, mushrooms, and meat so eating a diet high in these whole foods is key to getting enough zinc. Like vitamin C, zinc supplements are often used once a person becomes ill, but keeping zinc levels up through your diet means supplements won’t be needed to reverse a deficiency later on.
7. Probiotics (Bonus Tip)
Although probiotics are not actually micronutrients, they are important living microorganisms that reside inside our digestive track (gut microbiome) that help to support our immune system. Specifically, our gut "microbiome" has been found to positively influence our immune system and can induce regulatory T cell activation (10).
A healthy human being should have approximately 100 trillion good gut bacteria living in the digestive tract, which equals about 3-5 pounds of friendly flora. While taking a probiotic supplement is useful, including naturally fermented foods in your diet such as cultured coconut, sauerkraut, kimchi, pickles, and other fermented vegetables is a better alternative.
Food sourced probiotics will benefit your immune system by providing a higher inoculation, a wider array of strains, and built-in prebiotics which they feed on.
What You Can Do Now
It’s important to remember that while no single food or nutrient can prevent or cure viral infections or other illnesses, consistently meeting requirements of key nutrients will support your immune system every day and reduce the risk of health issues.
What you eat on a daily basis matters!