What Does It Even Mean to Have a Healthy Immune System?

The basics are complex.

Immune cells

We've all got friends and family who brag about their immune systems. Online, there's no end to the trolls who cite "diet and exercise" as their secret weapon against every disease. They have cabinets filled with supplements and extracts. And yet, parents everywhere are scrambling for something in a bottle to keep their kids from getting sick so often.

Does anyone in your family know what a lymphocyte is?

Probably not.

I've spent my entire life hearing phrases like "strong immune system," but I never really knew what that meant. Then I got a lymphocyte panel done. I figured out how to interpret the results, and they fit with my experiences. I have a decidedly average immune system. I have one that's prone to an inflammatory response, and it doesn't have a great memory. It tends to forget what it saw recently, and it launches an all-out assault. In a strange way, it's comforting to see what you've lived reflected in actual lab results.

If I had to grade my immune system, I'd give it a C.

I also got curious about what exactly it means when someone talks about their diet and their immune system. By and large, Americans overestimate their health, and they describe their diet as healthier than it really is. I have cousins who think it's healthy to eat bacon and steak all the time. Often, these grandstands about diet and exercise are just platitudes thrown in the faces of the vulnerable as excuses for why they get sick. They think they know what makes a healthy immune system. I don't think they do. I think they're all guessing.

I wonder what people would think if you subjected their "healthy immune system" to a full analysis, including a breakdown of their diet.

Would they be so confident then?

For example, if you want to build up your B cells then you need to eat carbs. A 2021 study in iScience found that keto and protein diets inhibit B cell growth because they deprive your body of quick energy.

Does the average American know that?

Probably not.

Most westerners think of their immune system as a muscle, and they're wrong. You can't train your immune system by exposing it to diseases, especially ones that damage your immune system. You can eat your way to a healthier immune system, but it's not as simple as it sounds.

A 2023 article in Pharmaceuticals gives a good overview of the main nutrients and supplements that help your immune system. There's nothing too controversial here: vitamin C, vitamin D, vitamin B9 (folic acid), magnesium, zinc, and selenium. They recommend echinacea and garlic for improving gut health. Finally, they recommend melatonin for a range of benefits, including "increasing the proliferation and maturation" of T and B cells. This isn't the stuff of snake oil and fairytales. These are things your body needs.

Vitamin A

A 2019 article in Nutrition and Immunity says vitamin A "plays a crucial role in the development and regulation of the immune system." Several other studies over the last hundred years have shown that it's important "in the generation of innate and adaptive immune cell response." It stimulates the production of white blood cells, strengthens your internal organ lining, and helps your body produce mucous. At the same time, too much vitamin A can cause your immune system to "forget" pathogens it's seen.

Best sources: Kale, spinach, broccoli, carrots, sweet potatoes, pumpkin, butternut squash, cantaloupe, mango, eggs, milk.


Researchers have known for 20 years that your body needs iron to produce immune cells, especially lymphocytes. New research has also found that it helps regulate immune cells and contributes to a healthy gut microbiome. It's one reason why iron deficiency (anemia) results in more infections.

Best sources: Beans, lentils, spinach, nuts, seeds, enriched rice and bread, most meats, including fish, oysters, and mussels.

Vitamin C

You know you need vitamin C, but why?

A 2020 article in Frontiers in Veterinary Medicine addresses a range of nutrients and supplements your immune system needs. I know it's weird to get nutrition advice from vets, but they explain it well. They're specifically talking about Covid. We've all heard that vitamins C and D boost your immune system, but we don't think about the details. Well, vitamin C "takes part in the development and functionality of various immune cells and the production of antibodies." It also "enhances the epithelial barrier against pathogens." In other words, your immune system needs vitamin C to produce white blood cells. It's also good for the lining of your internal organs.

That's backed up by a 2018 study in Antioxidants. As the authors write, "an increasing body of evidence indicates that AA [vitamin C] positively influences lymphocyte development and function." A 2022 study at Ohio State also found that vitamin C plays a major role in B cell differentiation. You'll find evidence scattered across other studies. Most doctors acknowledge the importance of vitamin C. It's widely recognized that while vitamin C won't prevent you from getting sick, it absolutely helps you fight off pathogens. That's because your body needs vitamin C to produce T and B Cells. In fact, viral infections deplete your body of vitamin C, which is why it's important to keep those levels up.

Most people can handle about 1000 mg of vitamin C a day, but Harvard Health recommends 75-90 per day.

Best sources: Oranges, lemons, kiwis, bell peppers, strawberries, tomatoes, broccoli, cabbage, cauliflower, brussels spouts, potatoes.

Vitamin D

According to a 2020 article in Nutrients, almost every cell in your immune system has a vitamin D receptor, and vitamin D3 in particular can help your immune system fight off viruses like Covid. Unfortunately, a lot of us border on deficiency. According to Nutrients, 61 percent of American children and 40 percent of adults don't get enough vitamin D.

A study in Japan found that children who took a 1200 IU supplement of vitamin D saw 40 percent less flu A than the placebo group. Generally, research shows a clear link between vitamin D and immune function.

Your body can generate vitamin D from safe exposure to direct sunlight. You can also get it from foods and supplements. Nutritionists recommend 600 IU per day, or 7-30 minutes of sunlight. You have to be careful. Too much vitamin D can lead to heart and kidney failure. Unless a doctor says otherwise, keep your intake well under 4000 IU per day.


According to the research, zinc helps regulate your immune system. A 2020 study in BBA confirms that zinc shows "broad antimicrobial activity." It can play a major role in "inhibiting viral replication," and it specifically "has been previously shown that zinc can inhibit SARS RNA polymerase."

Zinc deficiency can affect up to 20 percent of the global population.

Zinc works better with zinc ionophores that facilitate their uptake. Curcumin "acts as a natural zinc ionophore." So, zinc plus curcumin can fight "many RNA viruses." As they state, a daily 30 mg zinc supplement boosts T cell numbers and helps inhibit the replication of certain viruses.

Best sources: Fortified juices and cereals, cod liver oil, salmon, tuna, sword fish, fortified milks, liver, egg yolk.

Omega-3 fatty acids

Research has found that omega-3 fatty acids help your body produce and maintain a healthy number of macrophages. According to a 2022 article in Springer Nature, macrophages "function in the defense against pathogens and in the clearance of old senescent, or dead cells." They form a first line of defense against viruses and bacteria. They also help initiate your T and B cell response.

A 2019 article in the International Journal of Molecular Sciences reviews several studies showing omega-3 fatty acids can help your body produce more macrophages, but they can have an unintended impact on your T and B cells. They seem to help with autoimmune disorders, and that suggests they repress parts of your immune system, so you want to take a light approach.

Common sources: Fish oil, garlic, cranberries, broccoli


It's kind of a no-brainer, but your body needs sleep to function, and that extends to your immune system. Specifically, the Sleep Foundation cites studies that sleep promotes adaptive immunity. It builds your immune memory. If you aren't getting enough sleep, it can hurt your immune system's ability to remember and react to antigens it's seen before. A 2021 article in Communications Biology found that most people don't get enough sleep, and it puts them at a greater risk for all kinds of infections and chronic illnesses.

Other supplements

You can find plenty of information on supplements and remedies like elderberry and manuka honey. The research is mixed. They're generally good for you, but there's not strong evidence that they do much for infections. They can give you a little boost, but that's about it.

Consuming more polyphenols can help your immune system produce more T and B cells while protecting against free radicals (Nutrients). You can find these polyphenols in fruits and vegetables as well as green and black teas, roots, and seeds. Apart from protein, you can take arginine and glutamine to increase T cell production. Nucleotides can help build and protect T cells, including natural killer cells. They also help build resistance to secondary infections, especially candida, a post-Covid problem that's becoming more common.

Your immune system also needs B vitamins, selenium, phosphorous, and calcium to produce and regulate immune cells. They're essential. For example, B12 plays an important role in the development and activity of natural killer and CD8 cells. The Harvard School of Public Health's website gives you a breakdown of all these vitamins and where to get them.

What about probiotics?

Doctors do find probiotics useful, but you have to be careful. You have to match probiotics with needs. There's generally no problem with lactobacillus, and it can enhance your gut health and diversity. They mostly seem to balance your body's inflammatory responses. Some doctors warn against them because they can disrupt your microbiome. If you want the benefits of probiotics without the risks, try yogurt and other fermented foods.

The bigger picture

We know what's not good for your immune system: Smoking, drinking, processed foods and sugars, lots of stress, and lots of work. We've all heard about the importance of sleep and a healthy diet. For many of us, the problem is access. It's hard to get enough sleep if you work multiple jobs or have to take care of someone. It's hard to eat healthy if you live in a food desert where stores don't sell fresh food. It's also hard to eat healthy if your workplace expects you to be in the office all the time.

Let's face it, the larger systems we live in make it difficult to do the right thing for our bodies. We get blamed for poor habits. And of course, everyone wants to take advantage of us, all the time. When you go to the store, the advertisers aren't pushing broccoli.

They're pushing supplemental oxygen.

My point here isn't to exhaustively explain everything that goes into an immune system. It's to make a point. All I did was explore a tiny piece and found there's a lot of nutrients your body needs. If you have too much or not enough, then it's not going to perform like it should.

Somehow, I doubt everyone who brags about their healthy diet is eating kale, spinach, and carrots every day. I doubt they know all the nutrients their immune system needs and where they come from.

Maybe I'm wrong.

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