Immune System Booster Foods – Sharon Palmer, The Plant Powered Dietitian

What are immune support vitamins? What are immune boosting foods? And what are the worst food ingredients for immune system? I’m answering all of these questions on eating to boost immunity in this guide.

Immune boosting foods that power up your immune defense are a hot marketing tool. From food products and dietary supplements that claim to “support immunity” to magazine articles that recommend top “immune superfoods,” it seems the idea of eating to boost immune function is everywhere. Perhaps it’s a good thing, as infectious diseases are the leading cause of morbidity in the world. And given pandemic outbreaks, along with cold and flu season, it’s tempting to buy into the hope of eating your way to a stronger immune system. While good nutrition can indeed help support immune system, it’s important to separate hype from fact. So, let’s dive into the science on vitamins for immune system for adults, immune support vitamins, and immune boosting foods.

This Is Your Immune System

You can credit your immune system for allowing you to thrive within a busy, interactive world. The immune system is your body’s protective network that fends off invasion by harmful substances, such as bacteria, viruses, and chemicals, as well as guarding against the development of cancer. When your immune system is healthy, you have multiple barriers to protect against invaders, including your skin, inflammatory responses, and specific immune responses, such as certain types of white blood cells that destroy pathogens.

Your gut plays a very important role in your immune system; it is the largest immune organ in the body, accounting for 25 percent of your immune cells. More than 400 species of bacteria reside in the gut, and they have important symbiotic (beneficial) relationships with your body. Simin Meydani, D.V.M., Ph.D. director of the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) and the Nutritional Immunology Laboratory at Tufts, calls the gut flora (the collection of microorganisms, mostly bacteria) “the forgotten body organ.” Learn more about your gut microbiota here

As you age, your immune system diminishes. Meydani reports that there is an increased incidence of infectious disease (and morbidity and mortality from infectious disease) in older adults because they are more susceptible, the pathogens are more virulent, and there is a negative change in the gut bacteria. To top it off, marginal nutritional deficiencies also are common in older adults.

And once you have an infection, a vicious cycle kicks in—the infection obstructs your ability to boost nutrition because of loss of appetite, fever, and diarrhea, thus your immune system weakens. To make matters worse, scientists now know that nutritional deficiencies can cause a virus to become more virulent.

This Nourish Lentil Bowl is packed with vitamins and minerals important for immune health.

Nutrition and the Immune System

One of the most important ways to maintain a healthy immune system is to power up on good nutrition. “When a pathogen enters the body, the immune system recognizes it and the body produces an army of specialized immune cells to get rid of the pathogen,” explains Meydani. And what do the immune cells need in order to grow in numbers? “Essential nutrients like vitamins, minerals, amino acids and essential fatty acids,” she adds. This is the root of the diet-immunity connection. “Nutrients are essential for the optimal function of the immune response and to prompt a defense against pathogens. Deficiencies of nutrients, as well as aging, can impair the host’s defense and increase the occurrence of pathogens,” says Meydani.

Build Up Your Immune Defense with Diet

The following nutrients show promise for their effects on the immune system.

This Chipotle Tomato Rice Power Bowl is packed with vitamins and minerals linked with immune health.

1. Vitamin C

Many people believe fervently that high levels of vitamin C boosts their immune function and helps fight colds. Unfortunately, the science has been far from concrete, with some studies showing that it enhances immune function, and other studies showing no effect. According to the National Institutes of Health, more than 30 clinical trials have examined the effects of vitamin C on cold prevention, yet overall they do not support a significant reduction in risk. Still, it’s important to get enough of this antioxidant vitamin in your diet through foods, so make sure to include daily sources of vitamin C-rich foods, such as papaya, red peppers, broccoli, strawberries, citrus and tomatoes as part of your healthful diet.

2. Vitamin E

It’s documented role in the immune system has led immunology researchers to study vitamin E. In a study led by Meydani and published in The Journal of the American Medical Association, vitamin E supplementation was found to reduce the risk of upper respiratory infections, in particular the common cold. Foods packed with vitamin E include nuts, olives and leafy greens.

This recipe for Tofu Mole with Brown Rice contains zinc.

3. Zinc

Studies show that people with low serum zinc levels experience twice the frequency of pneumonia (as well as longer duration and more antibiotic use,) compared with those who have adequate zinc levels, according to Meydani. In a study in the American Journal of Clinical Nutrition, zinc supplementation resulted in 65 percent fewer occurrences of infection. But when it comes to the common cold, Meydani says, “The jury is still out. Some studies show zinc helps and reduces duration of colds, while other studies don’t show that effect.” It’s still a good idea to make sure you are getting adequate zinc in your diet to support a healthy immune system, including plant-based sources like beans, nuts, and whole grains. 

4. Vitamin D

While we need more evidence, scientists recognize that the sunshine vitamin may have important functions within the immune system. Research shows that patients with tuberculosis respond better when treated with vitamin D or sunlight. In addition to sunlight, you can find vitamin D in fortified foods and beverages, as well as mushrooms exposed to light. Pescatarians can find it in salmon and sardines.

5. Calories

The potential immune benefits of calorie restriction have attracted the interest of researchers. In the CALERIE Study (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy Study) overweight participants divided into two groups reduced their calorie intake by 10 percent and 30 percent, for six months, resulting in significant improvements in immune response in both groups, with the best effects seen in the 30 percent group. “I’m not recommending that people who are not overweight would benefit from calorie restriction. Eat enough, but not too much,” urges Meydani. If you decrease calories too much and it results in nutritional deficiencies, it’s not good for the immune system.

6. Probiotics

These live microorganisms can exert health benefits by improving the number of beneficial bacteria in the gut. “Several studies show that the right types of probiotics increase the immune response,” says Meydani. A study in The Journal of Nutrition found that a fermented milk drink containing the probiotic lactobacillus casei strain Shirota significantly increased natural killer cell (an important immune cell) activity. However, only certain strains of probiotics have been tested for immune benefits; thus, it’s important to look for clinical proof.

Sonoma Kale Salad with Red Grapes and Mushroom-Red Wine Vinaigrette

7. Mushrooms

Mushrooms have captured scientists’ attention in immune research. When mice were fed a powder made of white button mushrooms, the natural killer cell activity increased significantly, according to a study published in The Journal of Nutrition. It’s a good idea to include mushrooms in your diet more often.

The bottom line

So should you take mega-doses of essential nutrients to boost your immune system?  “We can’t say with certainty. Sometimes if you supplement at more than the required level of nutrients, the immune function can decrease. It’s not always the case that more is better,” says Meydani. In addition, nutrients appear to impact people’s immune systems differently. Meydani explains that people can be “responders” or “nonresponders” to particular nutrients, based on genetic differences.

Many food companies and the media have made overly exuberant claims about the ability of particular foods to power up your immune system. It’s important to keep in mind that foods contain a synergy of nutrients that work in unison to provide health benefits versus supplements which only provide one or two nutrients. The best approach for fostering a healthy immune system is to eat a nutrient-rich diet that meets all of your body’s needs. Here’s more reason to make every bite count, with delicious, whole foods bursting with nutrients.

Check out the following blogs on how to build up your immune defense:

Top 5 Ways to Use Mushrooms
Learning All About Probiotics
Feed Your Gut Micobiota for Health

Written by Sharon Palmer, MSFS, RDN 

Image: Watermelon Poke Quinoa Tofu Bowl, Sharon Palmer, MSFS, RDN

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