We’ve all heard the phrase “An apple a day keeps the doctor away,” but is there actually some truth to this and if so, how does this work? Well, to be fair, you do need much more than just an apple to be healthy and to stay out of the doctor’s office, but the overall theme here is that a nutritious diet can keep you healthy for longer and that is true! But what is the actual science behind this concept? How does your nutritional intake really impact your health and more specifically, your immune function? We will explore how nutrition affects you on a cellular level, but first, we have some important questions to answer about immunity below.
Why is immunity important and how does it work?
Well, the first question is simple: immunity keeps us healthy and allows our body to fend off pathogens that could otherwise wreak havoc on our bodies or at worst, end our life. The answer to the second question is not so simple: to answer that question fully we may need to write a 5,000 page book on the topic because that is how complex and sophisticated the immune system is! Although a lot is known about the immune system, to this day researchers and scientists are still rigorously working to understand the immune response in its’ full capacity. For now, we won’t focus on the unknowns, but rather the knowns about the immune system. Having a basic understanding of immunity will help us understand specifically how nutrition impacts its’ ability to function properly.
Your immune system is comprised of 3 different layers: The first is physical which includes barriers, both internal and external. These include your skin and the epithelial lining of your GI tract and your respiratory tract. (2) The second layer is biochemical which is made of secretions and gastric acids. The third layer of immune protection comes from the cellular level such as B cells, T cells, antibodies and granulocytes to name a few (2). All of these layers work in conjunction together as either an innate response or an adaptive response. These are the 2 main branches of the immune system in terms of function. The innate system is the first and immediate response to a threat to our body. The innate system uses phagocytes, neutrophils, eosinophils, mast cells and dendritic cells to function. (1) This response is immediate which is important in addressing pathogens right away, but it is not specialized which is where the adaptive system shines. The adaptive system, as you may guess, adapts over time to different pathogens. This system recognizes pathogens, learns them and remembers them for future use so that if the pathogen invades your body again your immune system will know how to protect you. The adaptive immune system uses T cells and B cells to mediate the immune response (8) Nonetheless, both systems are imperative for a healthy immune response.
Why is nutrition important?
The relation to immunity and nutrition has been clearly established in the sense that the immune response is compromised when nutrition is not adequate. This can lead to an increased chance that you will develop an infection or illness. (2) An overall healthy diet is important for immune function, but more specifically is the importance of caloric intake, micronutrients and gut health.
When you think of a difficult workout you are going to embark on, you usually consider what you have eaten for the day and evaluate if what you have eaten is going to be enough for you to have a successful workout- your immune function is no different! When getting ready to “gear up” to address infection, your body must have proper nutrition to carry out all of the complex functions it needs to address the infection or illness properly. When your immune system is activated it requires a much higher need for energy for optimal function. Proper nutrition during times of infection or illness allows for your cells to function at their highest capacity on the cellular level, increasing the likelihood that your body will be able to properly address and eliminate the pathogen or threat to your body. Without proper nutrition your immune response will not be as strong as it requires which can lead to longer recovery times and ongoing infection and illness. (1)
Not only is your immune system impacted by the amount of calories you consume, but the type of calories and foods you consume matters just as much! Micronutrients have been widely known to have a positive influence on health and be necessary for the prevention of disease. Regardless of your age, it has been established that Vitamins A, C, D, E, B2, B6, B12, folic acid, beta carotene, iron, selenium and zinc all have an imperative role in immunity. (2) Examples of how specific micronutrient deficiencies can alter the response of the immune system can be seen with zinc, vitamin A and vitamin C. A deficiency of vitamin C can increase the likelihood of developing infections like pneumonia due to the absence of the antioxidant effects addressing the oxidative stress the infection is causing. A zinc deficiency can lead to a reduction of lymphocytes, one of the main immune cells, and it can also increase inflammation and oxidative stress. This is due to its’ effect on cytokine production, an important component of modulation of the immune response. (2) A deficiency of Vitamin A can lead to a reduction or alteration of function for macrophages, T cells, B cells and neutrophils; all important cells that assist in immune function. Evidence suggests that supplementation for these specific examples of micronutrients discussed can improve outcomes and immune response. (2)
The bacteria in your gut have a strong influence on your immunity as they are closely linked together. The gut microbiome is so complex that researchers are having a hard time making exact conclusions on how the gut microbiome is related to immunity, but we do know that there is a link and it is important to consider when discussing nutrition and immune function.
The epithelial walls of our gut serve as one of the layers of immunity that we discussed earlier. This is considered part of the physical and biochemical aspects of our immunity. Our gut is filled with trillions of bacteria, some good and some bad, however, we need to have an abundance of good bacteria to act as a first-line defense of foreign pathogens that may enter our body and to eliminate them appropriately without doing us much harm. If you do not have a healthy gut microbiome you may develop leaky gut syndrome; a condition that may lead to outside pathogens entering you fully instead of being eliminated through your digestive tract- this may lead to immune responses such as inflammation and other diseases. (11). Focusing on fermented foods such as yogurt, kefir and kombucha can help replenish the good bacteria in your gut due to their probiotic content. Supplementation with a daily probiotic can also help replenish the good bacteria in your gut.
Overall, we can see how important nutrition is for our immune function! The best thing to remember is that there is no one food that is going to be the key to preventing disease and supporting your immune system. It’s important to focus on a wide range of foods full of different nutrients! Be sure to get plenty of colorful fruits and vegetables throughout your day and consider supplementation if you are not meeting your needs through diet alone.