How does good nutrition affect our immune system?
Good nutrition is not the sole determinant of our health, but neither is our immune system on its own. Our nutrition status and immune system are meant to work together. For example, malnutrition can lead to poor immune function. However, over-nutrition does not necessarily indicate stronger immunity.
Imagine your body is like a castle. Some castles may have an inherently stronger defense system built in, like a moat, just like how some people are genetically born with better immune systems. Castles also train their soldiers to be prepared, similar to how we can train ourselves with healthy habits, such as washing hands frequently or coughing into your elbow. Lastly, castles are better prepared for potential invasion when they have adequate supplies and soldiers, just like how sufficient nutrition can better prepare your immune system for potential illness.
As we explore the current research surrounding nutrition and the immune system in this article, it is important to note that we cannot generalize recommendations – advice for disease prevention may not apply to disease treatment and vice versa. This article will discuss prevention strategies, so stay tuned for treatment strategies in our next article!
At the New Crown Epidemic Briefing held on February 10th, the President of Wuhan Jinyintan Hospital said that the COVID-19 virus is a self-limiting disease. In other words, many patients can overcome this disease through their own immune system. Therefore, we need to ensure that our immune system is in its optimal state to fight illnesses.
The immune system is complex and is affected by many factors, including lifestyle, sleep, stress, smoking, and diet. Current nutrition immunological research found the following nutrients to be beneficial in regulating the immune system.
Nutrient mechanisms in immune regulation
Vitamin D can enhance the elimination of certain bacteria, viruses, and fungi by stimulating our inherent antimicrobial immune response. Vitamin D can be used clinically to alleviate autoimmune and inflammatory diseases. Adequate intake of vitamin D can help maintain/enhance the body’s ability to fight infections by promoting the innate immune response. Ultraviolet rays are limited during winter and most people become deficient in vitamin D during this time, which may reduce their immune function. Foods high in vitamin D include the following: eggs, milk, fish, and mushrooms. The elderly population, whose absorption of vitamin D is low, and people with limited sun exposure can consider vitamin D supplements under the guidance of a doctor or a registered dietitian nutritionist.
Vitamin E is a fat-soluble vitamin present in cell membranes and also acts as a chain-breaking antioxidant. The concentration of vitamin E in immune cells is high, thus protecting them from oxidative damage associated with high metabolic activity and high dietary polyunsaturated fatty acids. Early animal experiments found that vitamin E deficiency can weaken immune function while vitamin E supplementation can reverse this effect. Due to the presence of multiple interfering factors in human experiments, there is no concluding evidence regarding the influence of vitamin E on the immune system. Some studies found that supplementation with 200 mg/day of vitamin E for one year reduced the incidence of upper respiratory tract infections in the elderly who lived in nursing homes and were over 65 years of age. A double-blind study of elderly, conducted in the Netherlands, revealed that there was no relationship between vitamin E and the incidence of respiratory diseases; in fact, there was evidence that reported a greater degree of infection with vitamin E supplementation. Vitamin E rich foods include: nuts, such as almonds, sunflower seeds, vegetable oils, and avocados.
Zinc deficiency is common in developing countries and is the fifth major risk factor associated with bacteria induced diarrhea and pneumonia. Zinc is a key nutrient that maintains homeostasis of the immune system. Correcting zinc deficiency by supplementing zinc can reverse some damage to the immune system and reduce mortality from certain infectious diseases. According to current research, children and elderly are at high risk for zinc deficiency, which is related to an impaired immune function. This leads to increased morbidity and mortality in these populations. Zinc supplements may help solve this problem, especially for people with low serum zinc levels. Zinc rich foods include: shellfish, seafood, beef, pork, poultry, nuts, and whole grains.
Fish oil and omega-3 unsaturated fatty acids
There is ample evidence that omega-3 unsaturated fatty acids can help to regulate the cellular and molecular events involved in the activation of immune cells, especially those related to cell-mediated immunity. Omega-3 unsaturated fatty acids can regulate and protect against chronic inflammation. Foods rich in omega 3 unsaturated fatty acids include: salmon, sardines, linseed oil, nuts, and mustard oil.
Some studies observed beneficial effects of probiotics on immune and defense functions. The general consensus indicates that the beneficial effects of probiotics are related to their abilities to strengthen the intestinal barrier by maintaining normal permeability, to prevent the growth of pathogenic microorganisms in the intestine by competing for nutrients, and to attach to the intestinal epithelium to help regulate immune cell function and clear infection. Meanwhile, it also protects against infection through a variety of mechanisms/pathways. Probiotic rich foods include: yogurt, natto, kimchi, kefir, fermented soy products, etc.
Some people may ask, “does this mean that I have to take supplements to improve my immune system?” The answer is no, health supplements are not necessary. Excessive amounts or overdosing can have adverse side effects. Most studies found that natural food sources of the nutrients listed above are both safe and effective, whereas health products and supplements provide too highly concentrated amounts, easily leading to side effects. For example, most people believe that vitamin C has antioxidant effects and is often advertised as a supplement that can accelerate the recovery of colds (however there is no sufficient evidence behind this claim). Therefore, many people will take health products that contain a high concentration of vitamin C, thinking that because it is water-soluble, it will not be easily accumulated in the body. This belief is dangerous. Currently, the tolerable upper intake level of vitamin C is 2000 mg/day. Excessive doses of vitamin C increases the risk of kidney stone formation, especially for those with insufficient renal function. In special circumstances when a balanced diet cannot be achieved, such as food insecurity or severe food allergies and restrictions, then health supplements play a more crucial role in prevention and treatment of illnesses.
So what should we do?
In reality, it is impossible to calculate whether or not you have eaten enough of the nutrients mentioned above. In addition to including the above-mentioned nutrients in our diet, we can also practice other lifestyle habits that support a healthy immune system.
Ensure a balanced diet
This is the first principle of health and nutrition advocated by all registered dietitians world-wide. It does not matter if it is a domestic meal or a healthy dinner from abroad, the basic principle is to ensure health through a variety of foods. Please refer to the Chinese Dietary Guidelines for Health. The United States also uses a simple and easy-to-understand healthy plate concept for diet education to the general public. The healthy plate graphic illustrates that half the plate should consist of non-starchy vegetables and fruits, a quarter of the plate for starchy foods (with half of the starchy foods being whole grains), and the last quarter of the plate for high-quality protein. Of the three macronutrients (carbohydrates, fats, and proteins), carbohydrates should account for 45-65%, fats should account for 20-35%, and protein should account for 10-35% of total calories.
Eat colorful vegetables and fruits
Different colored fruits and vegetables usually contain different micronutrients to help reduce inflammation and regulate immune function. For example, anthocyanins, the compound that gives fruits and vegetables a red/violet/blue color, acts as a powerful antioxidant in the body. Orange and yellow fruits and vegetables are rich in β-carotene. This is converted into vitamin A to help maintain eye health (prevents macular degeneration and helps improve night vision), and has certain anti-cancer properties. Green vegetables and fruits are rich in folic acid and vitamin C. Many green leafy vegetables are also high in calcium. Most fruits and vegetables are rich in potassium, which helps improve blood pressure. In general, eating a variety of foods and minimizing selective eating habits can safely and effectively strengthen your immune system.
Probiotics are microorganisms that can enhance the health of the intestinal tract and help maintain the homeostasis of the gut microbiota. Approximately 80% of the body’s immune cells are found in the intestine. Emerging studies show that intestinal health has an effect on immune function. Therefore, when the intestinal tract lacks healthy bacteria or has imbalanced gut flora, the immune function may be reduced and the body will be more vulnerable to viral infection and minor diseases, such as the flu/cold. Increase your intake of probiotic-rich foods, including fermented dairy products such as yogurt, kefir, cheese, pickles, etc. Also pay attention to your intake of prebiotics (probiotic’s food source), which can help stimulate the growth of probiotics in the intestine and help maintain a balanced gut microbiome. This will benefit immune function/health.
Mushrooms are not only delicious and nutritious, but they also promote the division of immune cells. Some studies show that mushrooms can increase cytokine production, which helps the body fight off viral infections. They are also rich in polysaccharides which can enhance immune function. Similar to fruits and vegetables, mushrooms are rich in antioxidants that help reduce inflammation. Mushrooms also contain B-vitamins, including niacin and pantothenic acid, and the mineral selenium, all of which are beneficial to the immune system. Some common mushrooms include: flower mushrooms, maitake mushrooms, oyster mushrooms, cremini mushrooms, and white mushrooms.
According to a 2013 article published in the International Journal of Preventive Medicine, ginger is a powerful antioxidant with anti-inflammatory and anti-bacterial properties. Due to these reasons, ginger has a variety of dietary/health uses, which also includes fighting the common cold and flu. Ginger’s anti-inflammatory properties and anti-bacterial chemicals, including gingerol and shogaol, helps to relieve sore throats and fight cold/flu viruses. Ginger is a versatile ingredient; it is recommended to use ginger in stir-fried foods or stews and soups to help attain the health benefits mentioned above. If you have a cold, consider using a tablespoon of freshly chopped ginger for a cup of warm ginger tea!
Good nutrition can help the body achieve its ideal state and healthy habits can help us prevent illness. The information mentioned above is compiled based on existing data and emerging scientific research. As we become better informed of how to optimize our health and well-being, let us strive to continuously improve.
Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6340979/
Ascorbic Acid Supplements and Kidney Stone Incidence Among Men: A Prospective Study. https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/1568519
Immune Modulation From Five Major Mushrooms: Application to Integrative Oncology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4684115/
Anti–Oxidative and Anti–Inflammatory Effects of Ginger in Health and Physical Activity: Review of Current Evidence. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3665023/#ref13
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