There’s never been a more critical time to create and maintain a healthy immune system.
I’ve long approached immune health from a different perspective: The gut. If you’ve read my blogs or book Happy Gut ® , you know the crucial roles that your gut plays in immunity.
Most of your immune system, after all, is in your gut. Your small intestine lining houses about two-thirds of your body’s lymphocytes, the small white blood cells that create an immune response. Those lymphocytes form a powerful army that seeks out and destroys pathogens. These are the bacteria, viruses, and other microorganisms that cause illness. As lymphocytes travel throughout your body, they rally your immune system in other organs.
To keep a strong immune system, start with your gut. Dysbiosis — an imbalance between favorable and unfavorable bugs in the gut — can wreak havoc on your immune system. The patients I see with gut problems oftentimes get sick more often. When we fix their gut, their immune system becomes stronger, too.
What you put on the end of your fork dramatically impacts both your immune system and your gut, for better and worse. Eating a wide variety of foods with protective nutrients and phytochemicals helps support a healthy immune response. I’ve talked about many of those foods in Happy Gut ® .
Even when you’re eating the right diet — and let’s face it, most of us aren’t — you may not be getting the key nutrients you need to support immune health. My patients frequently ask me what key nutrients they need to defend against viruses and other bugs to keep a strong immune system.
I’ve found that most people are deficient in at least one of these nutrients . These are my top five go-to nutrients when I feel a cold or the flu coming on. They’re the ones I frequently “prescribe” to my patients when they want to do everything possible to keep their immune system strong. Following each of them are recommended doses for prevention and to increase your immunity.
Vitamin D was actually named before its mechanism of action was known. It is not a vitamin; it’s a hormone!
That distinction is important, because whereas vitamins act as cofactors for enzymes, hormones like vitamin D cross right into the nucleus of the cell where they influence gene expression. This workhorse nutrient plays a big role in your immune response.
Vitamin D carries a long history for fighting infections 1 . Interestingly, before antibiotics, vitamin D from cod liver oil and sunlight was used to fight tuberculosis 2 . In fact, since one of the main ways your body makes vitamin D is by the effect of UV light on the skin, it’s no surprise that even before they knew vitamin D existed doctors placed patients outdoors to get sunlight to help them recover from the 1918 flu pandemic.
Vitamin D is crucial for your gut , too. Optimal levels of vitamin D keeps your gut barrier strong. A strong gut means that things meant to stay within your gut, such as large proteins, do . When these things slip through your gut wall, on the other hand, an immune reaction can occur.
Vitamin D can also impact your microbiome, the diverse ecosystem living inside you comprising of trillions of probiotic gut bacteria that help maintain a healthy digestive system. The right quality and quantity of probiotic gut bacteria impacts your immune system, for better or worse 3 .
Vitamin D does a lot of other things: It also helps the gut absorb calcium and mobilize it to your bones, for instance, and lowers the inflammation levels that contribute to many diseases 4 . Unfortunately, many of us are:
Deficient in Vitamin D
42% of adults in the U.S
. in fact, according to a 2011 study
- 69% for Hispanics
- 82% for African-Americans
These deficiencies can impair your body’s ability to fight bacterial and viral infections, including respiratory infections 6 . Vitamin D deficiencies could trigger viruses such as influenza 7 . One report looked at almost 19,000 people. Those with lower vitamin D levels were more likely to self-report a recent upper respiratory tract infection than those with sufficient levels, even after adjusting for other variables 8 .
Ideally, you’ll get vitamin D from diet and sunlight. Unfortunately, very few foods contain good amounts. Those that do, such as fatty fish and egg yolks, are foods that most of us don’t eat regularly. Likewise, most people don’t spend enough time in the sun to make sufficient amounts. That makes a supplement the ideal way to get vitamin D.
Vitamin D comes in two different forms:
- Vitamin D3 , or cholecalciferol
- Vitamin D2 , or ergocalciferol
Vitamin D3 is the superior form to replenish vitamin D levels, because it is absorbed better orally 9 . Always check your levels 4 – 8 weeks after starting a supplement to assess your response.
Recommended vitamin D dose: 5,000 IU daily
Your body needs vitamin A , another fat-soluble vitamin, for vision, growth, development, healthy skin, reproduction, and a strong immune system 10 .
When you think about a strong immune system, you might include things like your spleen and gut. But so many other parts of your body protect against viruses and other foreign invaders that can create illness. Consider the mucous barriers that trap bacteria and other infectious invaders in your eyes, lungs, gut, and genitals. Vitamin A plays a key role in keeping these mucus barriers strong 11 .
Vitamin A supports white blood cells, which help capture and remove bacteria and other foreign invaders 12 . Supplementation can help reduce infectious diseases such as viruses 13 . Vitamin A can also support your immune system in other ways, such as lowering inflammation 14 .
Deficiencies, on the other hand, spell bad news for your immune system. Too little vitamin A can impair your body’s response to infection , for instance, so your immune cells can’t function as well 15 .
In food, Vitamin A comes in two forms:
- Animal Foods – including eggs and wild-caught seafood contain the active form of vitamin A 16
- Plants – provide inactive forms of vitamin A precursors called carotenoids 17
Your body contains two enzymes that convert carotenoids or inactive vitamin A into active vitamin A. Some people have genetic variations that can inhibit this conversion 18 , potentially creating vitamin A deficiencies. Gut health also plays a role here. Your small intestine converts beta-carotene into retinol 19 . Gut problems could inhibit this conversion.
To support gut and immune health, eat plenty of colorful plant foods , like:
- sweet potatoes
- broccoli sprouts
These provide the carotenoids that research shows can decrease your risk of heart disease, cancer, and more 20 .
But to get the most bioavailable, preformed vitamin A, you’ll want to choose animal sources such as eggs, grass-fed beef, and wild-caught seafood. If you’re not eating sufficient amounts of these foods, consider getting vitamin A from a fish oil source. Liver and fish oils are highest in preformed vitamin A 21 .
One word of caution: Too much vitamin A can be a problem for pregnant women. Always talk with your healthcare practitioner before you supplement during pregnancy.
Recommended vitamin A dose: 5,000 – 10,000 IU daily for immunity
When you feel a cold coming on, you might automatically reach for vitamin C. And for good reason: The cells within your immune system can accumulate and utilize this water-soluble vitamin. Optimal levels can even help reduce how long you’re sick 22 .
Among its specific benefits, supplementing with vitamin C can help prevent and treat respiratory and other infections 23 . But ideal levels of vitamin C can support your immune system in ways you might not immediately consider.
Consider your skin, the body’s largest organ and a barrier to the potentially damaging things you’re exposed to daily. Vitamin C helps protect your skin against pathogens and free radicals that can create damage 24 . Deficiencies, on the other hand, will reduce your immune system’s ability to fight pathogens. Low levels of vitamin C can make you more susceptible to infections . Infections, in turn, can significantly lower vitamin C levels 25 .
Healthcare practitioners are using intravenous (IV) vitamin C with patients with COVID-19 to support the immune system . Experts note that “intravenous high-dose vitamin C could be [a] safe and beneficial choice of treatment in the early stages of COVID-19.” 26 In fact, researchers in China are currently studying whether high-dose vitamin C is ideal for patients with severe COVID-19 27 . We expect those results in the fall of 2020.
Using high-dose IV vitamin C for infections isn’t new. One study published in 2019 looked at high-dose vitamin C infusions for people with severe infections. 28 These patients had sepsis, a potentially life-threatening condition when the body’s chemical response to an infection becomes out of balance. Sepsis can damage multiple organ systems. 29 They also had acute respiratory distress syndrome (ARDS), a severe condition that can lead to irreversible lung injury and death. 30
Researchers found a lower death rate at 28 days among people who received the high-dose vitamin C. This study didn’t look specifically at COVID-19 infections. However, the endpoints of severe infections are the same. Sepsis and ARDS are the most common conditions leading to intensive care unit admission, ventilator support, or death among those with severe COVID-19 infections. 31
With all the coverage about COVID-19, I’ve read some critics point out that not all studies support vitamin C’s benefits on the immune system.
Many of these studies had limitations , including:
- Not using enough vitamin C
- Taking vitamin C after a cold kicked in
- Using ascorbic acid, a synthetic version of vitamin C that usually comes from genetically modified corn. Many commercial brands of vitamin C also lack bioflavonoids.
In other words, getting ideal amounts of vitamin C is important, but so is getting the right form. Many oral forms of vitamin C are poorly absorbed, especially at higher doses. 32 The best form of oral vitamin C is liposomal C. This form adds a carrier to the vitamin C to help your body better absorb and utilize this vitamin. While IV-form vitamin C is better, research shows that liposomal vitamin C absorbs better than regular vitamin C supplements. 33
Because it’s water soluble, you can’t overdose on vitamin C. Your body will excrete any excess amounts. But don’t take too much at once! Vitamin C can cause loose stools and other gastric distress that can mess up your day! Start on the lower spectrum and gradually increase your intake.
Recommended vitamin C oral dose: 2000mg daily
Recommended IV dose: 7,500 – 15,000mg daily for 3 days (for sick patients) 34
This plant pigment — scientifically called a polyphenol — is found in foods including broccoli, apples, berries, grapes, some herbs, tea, and wine. 35
As a powerful antioxidant, quercetin helps the body fight the free radicals that can damage your cells and compromise immunity. Quercetin can help stimulate your immune system to fight viruses, reduce allergies, and lower inflammation. 36
Those benefits make quercetin ideal to fight the common cold, which is caused by several respiratory viruses. In fact, quercetin could be more effective than a vaccination to fight the common cold. 37 Quercetin can halt viral infections and replication with no serious side effects. 38
Studies show that quercetin could inhibit the early stage of influenza, the viral infection that attacks your respiratory system. 39 Other research shows that quercetin can halt respiratory viruses, including rhinovirus, which is responsible for most common colds. In athletes, quercetin can even reduce symptoms of upper respiratory infections after exercise. 40
One study found that Quercetin could:
- Lower inflammatory cytokines
- Lower lung inflammation
- Lower viral load
- Improve lung function
- Reduce susceptibility to influenza A virus infection and its severity 41
As a nutrient, quercetin works great on its own. I also like pairing it with other flavonoids such as epigallocatechin-gallate (ECGC), the active compound in green tea. These flavonoids act as signaling molecules.
Recommended quercetin dose: 1,000mg daily
Zinc is a trace mineral that plays a big role in your immune system on so many levels. In fact, researchers call zinc “a gatekeeper of the immune system” because nearly every immune cell is dependent on zinc . 42
Zinc helps regulate both the innate immune system, your body’s first line of defense against viruses and other potentially dangerous invaders. This mineral also helps out your adaptive immune system, a backup defense that kicks in when your innate immune system is overwhelmed.
Studies show that zinc can reduce the duration of cold symptoms, especially in adults. 43 Zinc status is strictly regulated by two transporting proteins. When either malfunctions, your immune system can become tremendously impaired. 44
Like with the other nutrients here, zinc deficiencies can hurt your immune system, impairing:
Process of phagocytosis
hen your immune cells destroy something harmful like a virus
- Think of phagocytosis as Pac-Man. The word — “phagos” = to eat; “kytos” = receptacle or basket — refers to the immune cell taking in the harmful organism, almost like swallowing it.
Production of cytokines
our immune cells secrete these messenger molecules
- Cytokines communicate inflammatory signals both inside and outside cells 45
Growth and function of lymphocytes
white blood cells and one of your body’s main types of immune cells
- Lymphocytes include T and B cells. B cells produce and secrete antibodies, which help activate the immune system to destroy pathogens. T cells can only recognize viral antigens outside the infected cells. B cells, on the other hand, can recognize the surface antigens of bacteria and viruses. 46
Zinc deficiencies can increase your risk of infections. 47 While deficiencies can create problems, more is not better. High amounts of zinc can impair the immune system similarly to zinc deficiencies. When it comes to nutrients, balance is always the key. 48
Zinc is also a powerful antioxidant. The inflammatory cytokines that certain immune cells release can increase free radical production. Increases in these cytokines could suggest zinc deficiencies. Supplementing with zinc can help your body better manage those free radicals and prevent the oxidative stress that damages your cells. 49
When your body is inflamed — say, when you’re sick — zinc can help prevent free radical overload. 50 Zinc can also indirectly impact your immune system in several ways. This mineral contributes to the production of many hormones, including thyroid and growth hormones. Your pancreas also contains a large amount of zinc, which helps regulate insulin secretion. 51
Zinc also supports your gut , too. Several studies show that this mineral can support the tight junctions within your gut wall for conditions such as crohn’s disease 52 and inflammatory bowel disease. 53 When those tight junctions become damaged, gut problems including leaky gut can surface.
Certain things can also inhibit how well you absorb this nutrient. Phytates are anti-nutrients found in certain foods including wheat. They can interfere with the absorption of zinc and other minerals. Since the production of stomach acid is dependent on zinc, having low stomach acid could be caused by a deficiency.
Getting the right form of zinc is essential, since this mineral does not cross the cell membrane easily. Quercetin can help zinc get into cells more easily, where this mineral has been found to block viral replication. 54 In other words, zinc is an essential mineral for blocking the spread of a virus once it enters and infects your cells .
Don’t take zinc supplements for more than three to six months without checking your zinc/ copper ratio. Taking too much zinc can deplete levels of copper, another important trace mineral. Be sure to ask your doctor to check both your zinc and copper levels, because it’s important to know what’s stored inside your cells.
Recommended zinc dose: 15 – 30mg daily with food
Even with the healthiest diet, I find that many patients lack one or more of these immune-supporting nutrients. The critical step is to replenish levels, since many people initially have deficiencies in at least one nutrient. Then, I focus on maintaining optimal levels of these nutrients to increase immunity.
Supplements make the most efficient way to get these vitamins, minerals, and other nutrients that support immune health and so much more. But you also want to choose the right supplements.
Unfortunately, many commercial brands contain poorly absorbed forms, don’t provide the right delivery system, and contain gut-damaging ingredients such as dairy and gluten. These and other problems mean that you’re not always getting the right amount of these nutrients to do their job.
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