Nutrition and Immunity: During the flu season or times of illness, people often seek specific foods or vitamin supplements that are believed to boost immunity. Vitamin C and foods like citrus fruits, chicken soup, and tea with honey are popular examples. Yet the design of our immune system is complex and influenced by an ideal balance of many factors.
Nutrition and Immunity
WHAT IS OUR IMMUNE SYSTEM?
On a daily basis, we are constantly exposed to potentially harmful microbes of all sorts. Our immune system, a network of intricate stages and pathways in the body, protects us against these harmful microbes as well as certain diseases. It recognizes
foreign invaders like bacteria, viruses, and parasites and takes immediate action. Humans possess two types of immunity: innate immunity (protective barriers such as our skin, mucus, stomach acid, enzymes, and immune system cells) and adaptive
or acquired immunity (a system that learns to recognize and attack a pathogen that enters our body).
However, a range of factors can depress the immune system, such as environmental toxins (e.g. smoke and other particles contributing to air pollution), certain diseases (e.g. autoimmune and immunodeficiency disorders), excess weight, chronic stress, lack of sleep, and poor diet.
DOES AN IMMUNEBOOSTING DIET EXIST?
Eating enough nutrients as part of a varied diet is required for the health and function of all cells, including immune cells. Certain dietary patterns may better prepare the body for microbial attacks and excess inflammation, but it is unlikely that individual foods offer special protection.
Each stage of the body’s immune response relies on the presence of many micronutrients. Examples of nutrients that have been identified as critical for the growth and function of immune cells include vitamin C, vitamin D, zinc, selenium, iron, and protein (including the amino acid glutamine). 1,2 They are found in a variety of plant and animal foods.
Diets that are limited in variety and lower in essential nutrients, such as vitamins and minerals, can negatively affect a healthy immune system. There is growing evidence that a Western diet high in refined sugar and red meat and low in fruits and vegetables can promote disturbances in healthy intestinal microorganisms, resulting in chronic inflammation of the gut, and associated suppressed immunity.
The microbiome is an internal metropolis of trillions of microorganisms or microbes that live in our bodies, mostly in the intestines. It is an area of intense and active research, as scientists are finding that the microbiome plays a key role in immune function. The gut is a major site of immune activity and the production of antimicrobial proteins.4,5 Our diets play a large role in determining what kinds
of microbes live in our intestines. A high-fiber plant-rich diet with plenty of fruits, vegetables, legumes, and whole grains appears to support the growth and maintenance of beneficial microbes.
Certain helpful microbes break down fibers into short chain fatty acids, which have been shown to stimulate immune cell activity. These fibers are sometimes called prebiotics because they feed microbes. Therefore, a diet containing probiotic and prebiotic foods may be beneficial. Probiotic foods contain live helpful bacteria, and prebiotic foods contain fiber and oligosaccharides that feed and maintain healthy colonies of those bacteria.
- Probiotic foods include kefir, yogurt with live active cultures, fermented vegetables, sauerkraut, tempeh, kombucha tea, kimchi, and miso.
- Prebiotic foods include garlic, onions, leeks, asparagus, Jerusalem artichokes, dandelion greens, less-ripe bananas, and seaweed. However, a more general rule is to eat a variety of fruits, vegetables, legumes (such as beans, peas, lentils), and whole grains for dietary prebiotics.
DO VITAMIN OR HERBAL SUPPLEMENTS HELP?
A deficiency of just a single nutrient can alter the body’s immune response. Animal studies have found that deficiencies in zinc, selenium, iron, copper, folic acid, and vitamins A, B6, C, D, and E can alter immune responses.
These nutrients help the immune system in several ways: working as an antioxidant to protect healthy cells, supporting growth and
activity of immune cells, and producing antibodies. Epidemiological studies find that those who are poorly nourished are at greater risk of bacterial, viral, and other infections.
Eating a good quality diet can prevent deficiencies in these nutrients. However, there are certain situations in which one cannot always eat a variety of nutritious foods, and certain populations that have increased nutrient needs. In these cases a vitamin and mineral supplement may help to fill nutritional gaps.
These supplements are relatively inexpensive, typically costing less than 10 cents per day. Studies have shown that vitamin supplementation can improve immune responses in these populations. 6-8 Low-income households, pregnant and lactating
women, infants and toddlers, and the critically ill are examples of groups at risk.
The elderly are a particularly highrisk group. The immune response generally declines with increasing age as the number and quality of immune cells decreases. This causes a higher risk of poorer outcomes if the elderly develop chronic or acute diseases.
In addition, about one-third of elderly individuals in industrialized countries have nutrient deficiencies. Some reasons include a poorer appetite due to chronic diseases, depression, or loneliness; multiple medications that can interfere with nutrient absorption and appetite; malabsorption due to intestinal issues; and increased nutrient needs due to hypermetabolic states with acute or chronic conditions. Diet variety may also be limited due to budget constraints or lower interest in cooking for one person; poor dentition (e.g. missing teeth, ill-fitting dentures); mental impairment; or lack of transportation and resources to obtain healthy food.
A general multivitamin/mineral supplement providing the recommended dietary allowances (RDA) may be used in these cases, unless otherwise directed by one’s physician. Megadose supplements (many times the RDA) do not appear justified, and can sometimes be harmful or even suppress the immune system (e.g. as with zinc). Remember that supplements are not a substitute
for a good diet because no supplements contain all the benefits of healthful foods.
We have known for a long time that nutrition is intricately linked to immunity and to the risk and severity of infections. Poorly nourished individuals are at a greater risk of various bacterial, viral, and other infections. Conversely, chronic or severe infections lead to nutritional disorders or worsen the nutritional status of affected people. Therefore, it is imperative for all of us to pay attention to our diet and nutritional status during the ongoing COVID-19 pandemic.
– Dr. Wafaie Fawzi, Dr. Walter Willett, and Dr. Ibraheem Abioye