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Several lifestyle factors influence the health and resilience of both innate and adaptive immune function. This series addresses them in three parts: Nutrition and Supplementation, Exercise and Movement, and Lifestyle.

Each of these categories is important for immune health, but it’s difficult to argue any single category is more or less critical than the others. They’re all intertwined in such a complex way that even modern science struggles to tease out what’s actually happening with acute and long-term immune function when certain interventions are implemented.

The process of achieving better immune health is simple. It may not be easy, but it is simple. We hope this guide helps.

Don’t “Diet”

To best support a strong, resilient immune system, eat a nutrient-dense diet. What does that mean?

  • Eat enough calories to maintain normal metabolic function.
  • Get most of your essential nutrients — vitamins, minerals, essential fatty acids, and amino acids — from wholesome, minimally processed foods whenever possible.
  • Supplement your food intake with high-quality dietary supplements so your body has a consistent supply of critical nutrients your diet may not be providing enough of.
  • Stay well hydrated by drinking more water than any other beverage.

Aiming for optimal nutrition means not approaching each day or each meal with a restrictive “dieting” mindset. You don’t need to fear of calories, fat, or certain food categories. Choose sources of nutrition based on their ability to provide more optimal amounts of nutrients to help you feel and function at your best and satisfy your energy and appetite needs.

Researchers have observed that prolonged calorie restriction, defined as two years of following a low-calorie diet, lowers white blood cell counts, which lowers immune system resilience.

Either over-training or under-nutrition may lead to an increased risk of infections.

Venkatraman, 2002

Without sufficient energy or quality nutrition, innate and adaptive immune resilience against any potential infection suffers. Your first lines of defense against pathogens cannot function as designed.

Training hard and dieting to get leaner may make you more susceptible to common cold viruses.

Put another way, nutrition and supplementation promote well-being, which includes enhancing your immune system function.

Eat a Nutrient-Dense Diet

Vegetables and fruits are critical sources of key vitamins, minerals, fiber, and phytonutrients, essential for innate and adaptive immunity.

Every major health organization has been urging us to consume an abundance of produce for decades. Yet, recent evidence from the CDC suggests only ten percent of adults eat the recommended amount of fruit and vegetables each day.

It’s important to note that the Recommended Dietary Allowances for each nutrient (RDA’s) are not based on specific requirements of the immune system and its ability to fight infection or control inflammation.

In the case of several nutrients, for example, optimal nutrient intake levels are actually higher for other body systems and cell types. For example, vitamin E, vitamin B-6, and zinc needs increase when the immune system is more active than normal.

Interestingly, the “Five A Day” vegetable and fruit recommendation doesn’t even get you to your optimal micronutrient levels.

You’d be better off eating upward of nine or more cups of produce per day, but even that amount might not be enough.

Don’t worry about measuring exact amounts of produce. Just fill at least half your plate at each meal with colorful vegetables and fruits. Or, eat a pile of produce the size of your head each day.

The following are some of the most important nutrients you need to maintain a strong immune system.

Immune System-Supporting Essential Nutrients

Vitamin A

Technically Vitamin A isn’t a single vitamin. It’s a group of fat-soluble, biologically active compounds known as carotenoids. Carotenoids support healthy mucus membranes (innate immunity), and are also critical for production and proliferation of white blood cells (adaptive immunity).

The top 5 food sources of these compounds are:

High-quality supplements should contain both pre-formed (retinyl palmitate) and vitamin A precursor (beta-carotene).

Vitamin C

Also known as ascorbic acid, vitamin C is a water-soluble compound humans cannot make so we must consume it through diet or supplements.

As an antioxidant, it supports your immune response by helping regenerate other antioxidants, particularly vitamin E. It also supports the absorption of non-heme iron.

The top 5 food source of vitamin C are:

  • bell peppers
  • citrus fruit
  • broccoli
  • strawberries
  • Brussels sprouts

Evidence suggests the current RDA (60mg/day) is far too low to produce immune-enhancing benefits. To fully support your immune system, you need at least 200 milligrams per day.

Interestingly, supplemental vitamin C only appears to help reduce the frequency of common colds in physically active populations, and much higher doses may be needed to help shorten colds in anyone infected with one.

Vitamin D3 (cholecalciferol)

To be precise, vitamin D isn’t an essential nutrient, meaning we don’t need to consume it. We synthesize cholecalciferol when exposed to sufficient amounts of UVB sunlight without protective sunscreen.

Vitamin D is more of a pro-hormone than a vitamin. Regarding immune system function, vitamin D supports innate immunity by inducing antimicrobial proteins and is involved in adaptive immune response by supporting normal inflammation levels.

The top food sources of cholecalciferol (Vitamin D3) are:

  • fatty fish like wild salmon or tuna
  • beef liver
  • egg yolks
  • fortified foods such as dairy and orange juice (although it’s almost impossible to achieve optimal intakes through any of these sources)

High-quality vitamin D supplements should supply the active Vitamin D3 (cholecalciferol) form of this nutrient.

Vitamin E

Vitamin E is actually a family of eight related fat-soluble compounds, classified as tocopherols and tocotrienols, that have roles in protecting the integrity of cell membranes from free radical damage (innate immunity). Vitamin E also helps regulate inflammation as part of your immune response to infection (adaptive immunity).

The top food sources of vitamin E are:

  • wheat germ
  • nuts and seeds
  • peanuts
  • spinach
  • broccoli

High-quality supplements should supply natural mixed tocopherol forms of vitamin E rather than cheap synthetic forms.

Folate

Folate is a water-soluble vitamin involved in replication of all cells, including immune system cells. It’s also important for producing sufficient cell-mediated antibodies and natural killer (NK) cells (adaptive immunity).

Top food sources of natural folate are:

  • beef liver
  • spinach and other leafy greens
  • black-eyed peas
  • asparagus
  • Brussel’s sprouts
  • avocado

Despite mandatory food fortification of grain products with synthetic folic acid, folate status in most of the population is still likely inadequate to promote optimal health. Un-metabolized synthetic folic acid may even be harmful to long-term cognitive health.

Quality supplement sources should include methylated folate rather than synthetic folic acid.

Vitamin B6 (Pyridoxine)

Vitamin B6 is a water-soluble vitamin involved in energy metabolism, helps regulate inflammation and has an influence on NK cell activity.

It’s critical for the synthesis of amino acids, the building blocks of antibodies. It also has roles in white blood cell production and differentiation.

Top natural food sources of Vitamin B6 are:

  • chickpeas
  • beef liver
  • fatty fish like wild salmon or tuna
  • poultry
  • potatoes

High-quality supplements of vitamin B6 provide the biologically active Pyridoxal-5-Phosphate form of B6.

Vitamin B12 (Cobalamins)

Another water-soluble B vitamin, B12 is important for energy metabolism and red blood cell formation. It also helps immune function in partnership with folate to modulate cellular immune response.

Top food sources of B12 are:

  • clams
  • beef liver
  • trout
  • wild salmon
  • tuna
  • beef
  • nutritional yeast

The best form to supplement is the methylated form called methylcobalamin rather than synthetic cyanocobalamin.

Copper

Copper has antimicrobial and antioxidant properties. It’s also involved in antibody production.

The best food sources of copper are:

  • beef liver
  • oysters
  • unsweetened cocoa powder
  • potatoes
  • mushrooms
  • cashews

While copper deficiency is rare, needs increase in physically active people. In supplements, look for chelated forms.

Iron

Iron is a mineral involved in cytokine production and can form highly toxic free radicals that can help kill bacteria. It’s a coenzyme for immune cell function.

The best natural sources of iron are:

  • oysters
  • white and kidney beans
  • dark chocolate
  • beef liver
  • lentils
  • spinach
  • tofu

Not everyone should supplement with iron, but if blood tests show you need more it’s best to use chelated iron.

Selenium

Selenium is a trace mineral that’s critical as an enzyme cofactor. It’s also used for DNA repair – part of NK cell function (innate immunity).

Selenium supports immunoglobulin production.

The best food sources of selenium are:

  • Brazil nuts
  • tuna
  • halibut
  • sardines
  • ham
  • shrimp
  • beef

Zinc

Zinc helps maintain skin and mucosal membrane integrity. It also plays critical roles in cellular growth and differentiation of immune cells.

During acute illness, zinc is especially important. Research has shown the use of zinc lozenges (75mg of elemental zinc per day) may reduce the duration of the common cold by about 3 days.

The top natural food sources of zinc are

  • oysters
  • beef
  • crab
  • lobster
  • pork
  • baked beans
  • (dark meat) chicken
  • pumpkin seeds
  • yogurt
  • cashews

When supplementing with zinc, look for bisglycinate chelate zinc since this form has high bioavailability.

EPA and DHA Omega-3 Fatty Acids

EPA and DHA Omega-3s are long-chain fatty acids that are critical for healthy cell membrane function.

In addition to being structural components of cell membranes, EPA and DHA have roles as signaling molecules to promote healthy inflammatory response to injury or infection.

Once thought to be only immune-suppressive, some evidence suggests omega-3s are also capable of boosting adaptive immune response.

The best dietary sources of EPA and DHA are:

  • wild salmon
  • herring
  • sardines
  • mackerel
  • trout
  • oysters
  • sea bass

Fiber

Fiber can be generally classified into soluble and insoluble types. Soluble fibers can be fermented by microbes in your large intestine while insoluble fibers largely pass through our intestines simply providing bulk to stool.

Fermentable soluble fibers are also known as “prebiotics.” They provide an energy source for microorganisms in your gut.

Microbes ferment certain prebiotic fibers to produce short-chain-fatty-acids (SCFA’s), which are then used by the immune system.

Prebiotic ingestion allows beneficial microbes to flourish in the gut, which also helps maintain the integrity of the gut barrier and gut-associated lymphoid tissue (GALT), which supports both innate and adaptive immunity.

Some helpful prebiotic fibers include pectins, glucans, inulin, and isomalto-oligosaccharides. These are found naturally in many plants, so depending on the volume of produce, whole grain, and legumes you eat, you may not need to add supplemental fiber to your diet.

Eat High-Quality Protein With Every Meal

In addition to eating a produce-rich, nutrient-dense diet packed with vitamins, minerals, and essential fatty acids, it’s imperative to eat high-protein to promote optimal immune system health.

Protein-energy malnutrition and/or deficiencies of single nutrients can impair production of key proteins involved in immune function.

Beisel, 1996

If you’re following a calorie deficit (whether through diet, exercise, or a combination of the two), protein intake is even more important. Energy and protein deficits break down healthy muscle tissue to supply amino acids needed to maintain immune function.

Severe cases of protein or energy malnutrition have been known to cause serious immune suppression, mostly in developing nations, but milder forms of such conditions are certainly possible in people who exercise intensely on a consistent basis while under-nourished.

The amino acids that makeup protein are critical as building blocks for everything our immune system relies on.

They are the building blocks of cellular organelles, cell membrane receptors, enzymes, antibodies, signaling molecules and structural tissues that make up protective barriers such as skin and mucus membranes.

Optimal protein needs are 1.4 to 2.0 grams per kilogram body weight per day, about double the current RDA at 1.4 to 2.0 g/kg/day.

At least one study investigating higher protein intakes and immune response showed better immune resilience and wound healing compared to lower protein intakes.

To simplify these protein recommendations, estimate your individual protein needs for more optimal immune function and exercise adaptation using 1 gram of protein per pound of body weight, or at least 1g/lb of ideal body weight per day.

Concerned about over-doing protein? Unless you have a medical condition warranting protein restriction there are several other benefits to consuming a higher protein diet.

Read more: High-Protein Diets: Health Benefits and Controversies.

Avoid Inflammatory Foods and Beverages

Alcohol

Alcohol can disrupt the structural integrity and permeability of the gut lining itself, allowing other inflammatory compounds to cross into the bloodstream. It can also alter the gut microbiome and all the downstream inflammatory and immune cascades influenced by our gut microbes.

Alcohol metabolism also depletes several vitamins and minerals, which may have indirect immune health impacts due to competing for nutrient uses with the immune system.

On top of that, alcohol consumption alters sleep quality or quantity in most people, which may have both short and long-term negative effects on immune resilience.

In the context of all the factors involved with healthy or optimal immune function, the evidence isn’t clear enough to recommend any alcohol use to promote immune health. In other words, it’s not necessary for proper immune function and may have too many potential ways of disrupting optimal immune function to justify regular drinking to help immune function.

Sugar and Sweeteners

Processed or added sugars are ubiquitous in modern diets and are widely recognized as less nutritious than whole-food sources of simple and complex carbohydrates.

Excess consumption of added sugars has been shown to encourage systemic inflammation and possibly suppress white blood cell counts or activity.

In mouse studies, short-term exposure to high sugar altered gut microbiota and monocyte function.

Artificial sweeteners are almost as common as added sugars in modern diets, but they’re known to not just lend calorie-free sweet taste to foods and beverages.

Aspartame, sucralose, and saccharin alter the gut microbiome in rodents and humans, so much so they are implicated as a causative factor in the development of insulin resistance. If the effects on the microbiome are this disruptive to insulin function, might they also shift gut and immune resilience as well? More research is needed in this area for sure.

Like added sugars and alcohol, there’s little to no evidence showing artificial sweeteners support optimal immune function, so they also fall under the “minimize or eliminate” intake category.

Take High-Quality Supplements

Why are supplements so important?

Supplementation with micronutrients may facilitate the immune system and compensate for [dietary] deficits in essential nutrients.

Venkatraman, 2002

Modern dietary patterns lack nutrient-dense foods. Even if we choose wholesome, minimally-processed foods, modern food is often less-nutritious than it was a few decades ago due to soil nutrient depletion and growing practices.

Nutrient needs to support optimal health and immune function are often significantly higher than established RDAs, especially in individuals who exercise regularly and are seeking optimal function.

A vitamin is a substance that makes you ill if you don’t eat it.

Albert Szent-Gyorgyi, Nobel Prize in Physiology & Medicine, 1937

Supplements can be confusing, and unfortunately there isn’t just one supplement that can optimize immune function by itself under all conditions (although vitamin D is a remarkable supplement on its own).

This section covers the most-well understood supplements for supporting immune health in order of relative priority.  There may be others that have shown promise or have anecdotal support, but if they’re not included in this guide they aren’t worth covering just yet. As always, we encourage people to start their supplement plan with our Foundational Five.

High-Quality Multivitamin

High-Quality Multivitamins are the most convenient way to consistently help cover essential micronutrient needs (vitamins and most minerals).

Remember from earlier that many of these nutrients come in different forms with different absorption and bioavailability characteristics, and that amounts needed to optimize immune health may be much higher than established RDAs.

Well-formulated multivitamins will not only use the best forms of essential nutrients, they’re also delivered via stable and easy-to-digest methods, namely as capsules instead of tablets gummies, or liquids.

Inadequate micronutrient intake, sometimes at borderline levels of deficiency, has been linked to stunted growth and neurocognitive deficits, as well as increased risks of various symptoms and [health] conditions. Most nutrients act in all tissues, and all tissues need all nutrients; therefore, inadequate intakes may adversely affect every body system.

Ward, 2014)

Read more: High-Quality Multivitamin: What to Look For. Why It Matters.

Fish Oil

EPA and DHA pmega-3s from fish oil. Most people fail to consume enough dietary sources of these essential fatty acids so supplements are critical for managing inflammation, supporting cell membrane function and supporting immune response.

The best outcomes appear when total EPA + DHA intake is at least 2000mg per day, so look for a highly-concentrated supplement with at least 600mg of EPA+DHA per softgel from triglyceride form omega-3s.

Read more: Fish Oil: Benefits of Supplementing For Your Body and Brain.

Vitamin D

Vitamin D is important to supplement for several reasons; there aren’t many foods rich in active vitamin D3, most people don’t get adequate sun to produce their own, and insufficient vitamin D has direct and widespread negative effects on innate and adaptive immunity.

Half the world’s population may be deficient, and even more have sub-optimal levels. Many multivitamins contain minuscule amounts of vitamin D so look for a supplement with vitamin D3 as cholecalciferol combined with vitamin K2 (menaquinone) as these nutrients interact to support several aspects bone and cardiovascular health along with immune function.

The Vitamin D Council recommends at least 5,000 IU per day for most adults.

Read more: Vitamin D: Deficiency Symptoms and Benefits of Supplementation.

Magnesium

Magnesium is recommended as an additional supplement because even high-quality multivitamin/mineral formulas often can’t physically fit enough of this mineral without increasing the number of capsules.

It’s critical for several aspects of innate and adaptive immune function as well as literally hundreds of other metabolic reactions.

Magnesium is also helpful for promoting sleep onset and sleep depth, which we’ll cover later. Look for chelate or malate forms of magnesium for best absorption and aim for at least 300 mg per day in addition to dietary intake for best effects.

Read more: Magnesium: Health Benefits and Best Ways to Supplement.

Digestive Enzymes

Digestive Enzymes aren’t nutrients per se, but they do play a vital role in helping us access the nutrition from the food and supplements we consume.

Enzymes, including digestive enzymes are also part of our innate immune system; they play a role in intercepting and destroying pathogens we may ingest.

Digestive enzyme supplements make this list because the nutrients we eat and take can only lend their benefits if we digest, absorb and assimilate them completely.

Take a broad-spectrum digestive enzyme that includes hydrochloric acid (Betaine HCl) along with carbohydrases, lipases, and proteases to help with breakdown of carbohydrates/fibers, fats, and proteins.

Read more: Digestive Enzymes: What Are They? How Do You Use Them?

L-Glutamine

L-Glutamine is the most abundant amino acid in our bodies, and while we can synthesize it from other amino acids it’s a “conditionally essential” amino acid, which means under certain conditions our needs are elevated to the point where optimal health can only be achieved if we take in extra sources.

Most importantly for immune health, L-Glutamine serves as fuel for most immune cells and immune response can be impaired when glutamine reserved become depleted and dietary intake is inadequate.

It’s an inexpensive, odorless, tasteless powder that can be easily added to any food or beverage, 5 grams twice a day as a general recommendation.

Probiotics

Probiotic supplements are sources of microorganisms that can shift the microbial balance of our lower intestine.

A recent meta-analysis showed that probiotic supplementation reduced the incidence of upper respiratory infections (URIs) by approximately half, shortened URI duration by approximately 2 days, and reduced antibiotic prescription rates.

Researchers are just scratching the surface of understanding which strains of bacteria are most helpful to each individual, so the type and amounts of colony-forming units (CFUs) to look for in a supplement isn’t as clear.

Well-researched strains will be indicated on supplement labels with a specific letter-number code after the name of the strain, such as Bifidobacterium bifidum (BI-04), which is a clinically studied strain shown to support healthy immune function (just one of the strains in Life Time’s MultiPro 30B Probiotic).

Other Supplements to Consider

Spirulina evidence that suggests that supplementing with the blue-green algae spirulina promotes mucosal immunity.

Melatonin may be a helpful nutrient to supplement to promote immune health indirectly through improving sleep onset and sleep depth.

Curcumin, a component of turmeric root may be powerful botanical ingredient that could help modulate immune response and cell signaling.

Overwhelmed? Don’t be.

The main takeaways regarding nutrition and supplementation are to eat a nutrient-dense diet with plenty of vegetables and fruit, get ample protein (probably more than you consume now), and upgrade/optimize your supplement routine.

Simple. Maybe not easy, but simple.

Keep the conversation going.

Leave a comment, ask a question, or see what others are talking about in the Life Time Training Facebook group.

paul-kriegler-registered-dietician-life-time
Paul Kriegler, RD, CPT

Paul Kriegler, RD, LD, CPT, CISSN, is the director of nutritional product development at Life Time. He’s also a USA track and field coach.

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