With the Delta coronavirus variant on the march and the common cold making headway due to some going maskless, there is no better time than today to start taking care of your immune system. The way to do that is to eat immune-boosting foods.

Yes, instead of asking your immune cells to take care of you, you can help strengthen your immune system's ability to respond–through healthy lifestyle choices and diet–by arming them with nutrients such as vitamins and minerals, antioxidants and phytochemicals that give your immune "killer" cells the ammo they need to complete their mission: To keep the body safe from invaders and disease.

According to a report in Harvard Health, the publishing arm of the Harvard Medical School, the best way to boost your body's immune system is to live a healthy lifestyle: Don't smoke, exercise daily, maintain a healthy weight, and eat more fruits and vegetables. But which ones are best at arming your immune system? Those high in vitamins A, B, C, and D vitamins, as well as beta carotene and minerals like Zinc and Iron, selenium, and more.

How to boost your immune system by choosing the right foods

Your immune system is like an army with different cells on missions to search and destroy invaders in the form of bugs that cause bacterial infections as well as viruses that are much, much smaller and can sneak by and go undetected for 24 hours or longer, by emitting proteins that fool the host. The Delta virus enters your lungs and bloodstream by latching on to cells and multiplying until these virus cells grow in numbers to become a threat. By that time, it's a race.

Which army will win? The good guys who are defending you or the bad guys who are attacking you? Here's how to tilt the game in your favor. Eat as many immune-boosting foods in a day as you can, and avoid the inflammation-causing foods such as processed meat, dairy, added sugar, and overly-processed foods (especially junk food) that make it harder for your armies to do their job.

Inflammation gets in the way of your immune cells, essentially causing what could be considered a traffic jam in every single major intersection and byway, creating havoc so the body's killer cells are too busy disposing of cellular waste to try and fight off invaders and can't do everything all at once. If your immune system gets overwhelmed it starts to lose out on the important task of keeping you healthy, from inside threats such as inflammation and disease and outside threats such as viruses.

Keep all systems clear and your immune cells strong, armed, and able to fight both internal threats such as diseases and external invaders with these 10 foods that use naturally occurring defenses (such as broccoli, which uses natural gas to fight off actual bugs in the garden, or grapefruit, trying not to burn up in the hot sun) to enter your body and protect it from bugs and oxidative aging.

Here are the top 10 foods to boost your immunity and reduce inflammation

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1. Leafy Greens, like Spinach, for vitamins A, C, and E and beta carotene

When researchers study the role of micronutrients and immunity they get encouraged by vitamin A's ability to boost both "innate" immunity and "adaptive" immunity, meaning the type that fights what's already happening in our body as cells grow, replicate and die (and the immune system carries them off to a safe demise) when cancer can take hold, as well as the immunity we need to fight off what's in our surroundings. Eat leafy greens such as spinach, kale, arugula, and chard, to enhance your immune function and boost your defense against infectious diseases.

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2. Red bell peppers, which provide the highest levels of vitamin C

Vitamin C has been studied ever since Linus Pauling, a chemist and doctor who won the Nobel Peace prize in 1954, suggested that large doses of C (upwards of 2,000 mg) could cure everything from the common cold to cancer. His research has been largely refuted since C is not the cure for heart disease, but what it does, by lowering inflammation, can contribute to lowering the risk of every major disease.

Studies show that moderate amounts of C lowers inflammation and even blood pressure, so perhaps Pauling was more right than wrong. "A moderate amount of vitamin C can significantly treat and reduce the inflammation, as measured by [C Reactive Protein] and [Interleukin-6] in hypertensive and/or diabetic adults and also helps to reduce [Fasting Plasma Glucose] levels. So not only does C reduce inflammation but also blood pressure and even blood sugar, this study found.

Now scientists believe that lower doses of vitamin C do just as well, or even better, to help support the body's immune system, and the vegetable with the most vitamin C is the red bell pepper. Each pepper contains152 mg of vitamin C, or three times as much as an orange (51 mg), as well as beta carotene and vitamin A, folic acid and fiber. Eat just half a red bell pepper a day and you'll get the recommended daily dose of 65 to 90 mg of vitamin C in a day.

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3. Citrus fruits including kiwis and papayas, for C and other vitamins

While red peppers may be king when it comes to vitamin C (with 152 mg per red pepper) you can get plenty of C from oranges (51 mg), grapefruits (38 mg), kiwis (64), papayas (234), and lemons (31 mg) or limes (20 mg), so pile these into your fruit salads throughout the day to reach your recommended amount of 65 to 90 mg of vitamin C a day.

Studies show that vitamin C is a powerful anti-inflammatory agent in the body since it interferes with the "pro-inflammatory cytokines" which we know now after the coronavirus pandemic are drivers of inflammation, and can over-react in the face of invaders like viruses, causing more problems for the host than the bug itself.

"Moreover, vitamin C is an antioxidant that protects the immune cells," wrote the authors of one study into how C works to support the immune system. "Vitamin C as an enzymatic cofactor is extremely important in maintaining tissue integrity and plays a crucial role in formation of skin, epithelial and endothelial barriers."

Citrus fruits are also full of other vitamins from A to metabolites that help your body fight infections, studies have found. Those beneficial compounds include flavonoids, alkaloids, coumarins, limonoids, carotenoids, phenolic acids, so eat the fruit (rather than just the juice) for the full array of benefits, including fiber.

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4. Apples, rich in soluble fiber, which has been shown to boost immunity

Apples are the reigning prince of fruit when it comes to fiber, with 4.4 grams per fruit, which helps shift your microbiome to lower inflammation and fight diseases from heart disease to diabetes and even cancer. The more fiber in your diet, the more your immune cells can sweep for "other problems" including attacking agents like viruses or other infections.

To understand the role of soluble fiber and immunity, scientists studied how fiber can help shift the gut microbiome to lower inflammation in the body and strengthened immunity in a study that showed the immune cells "change" from having to work on inflammatory diseases to instead focus on invaders from outside.

"Soluble fiber changes the personality of immune cells -- they go from being pro-inflammatory, angry cells to anti-inflammatory, healing cells that help us recover faster from infection," said Gregory Freund, a professor in the U of I's College of Medicine and a faculty member in the College of Agriculture, Consumer and Environmental Sciences Division of Nutritional Sciences, quoted in Science Daily. This happens because soluble fiber causes increased production of an anti-inflammatory protein called interleukin-4, Freund added.

Soluble fiber is in apples, oats, as well as black beans, broccoli, pears, sweet potatoes, figs, avocados, nectarines, and flax seeds, sunflower seeds as well as other fruits and vegetables.

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5. Broccoli, with sulforaphane to help fight bugs in the garden and in your body

Sulforaphane is released when the broccoli stem or leaf is damaged, to help repair it and also fight off whatever damaged it in the first place. It also is found in other cruciferous vegetables like cauliflower, cabbage, and Brussels sprouts and it's what gives these vegetables their distinctive odor when cooked. To get the most benefit, don't overcook your broccoli since it essentially kills and deactivates the gas, so instead lightly steam it and eat it nearly raw.

In one study, broccoli was found to have the highest sulforaphane effect on cells and was most effective in fighting off the pro-inflammatory responses in the body. This, combined with other powerful antioxidants in broccoli, make it a powerful disease-fighting immune booster.

In one study, published in the journal Cell, called "Eating green veggies improves immune defenses," researchers studied the protective cells that lie under the skin and all the surfaces of your body, called epithelial cells that act as protective layers. They found that when mice were fed a vegetable-poor diet for two to three weeks, 70 to 80 percent of these protective cells disappeared. "It is still surprising to me," said Marc Veldhoen who was the study's lead author, of The Babraham Institute in Cambridge. "I would have expected cells at the surface would play some role in the interaction with the outside world, but such a clear-cut interaction with the diet was unexpected."

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6. Blueberries, beets, pomegranate, and other purple fruit with phytochemicals

That beautiful blue hue that makes berries so enticing is created by a phytochemical called anthocyanins which also gives other purple fruit their coloration. Studies have shown that "regular, moderate intake of blueberries and/or anthocyanins with reduced risk of cardiovascular disease, death, and type 2 diabetes, and with improved weight maintenance and neuroprotection."

Just one-third of a cup of blueberries a day is enough to see all the benefits, research has shown. Blueberries also have anti-inflammatory, antioxidant, and vasoprotective effects, the studies have found, and have a "regulating effect on glucose delivery to insulin-sensitive tissues" so they help regulate the cells' metabolic function.

One of the superpowers blueberries have is to help your immune system's T-cells recognize cancer cells, so blueberries are being studied as a way to support and promote cancer treatments in patients. "Their wide spectrum of phytochemicals suggests that they might influence the functions of multiple immune cells and different aspects of cancer immunity," the researchers wrote in a study called An immunological perspective for preventing cancer with berries. "Therefore, the potential of berries to aid cancer immune-therapies by, for example, regulating dendritic cells, warrants further investigation in animal and human studies."

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7. Mushrooms, high in minerals such as zinc, selenium and B vitamins

Mushrooms may be the most overlooked food when it comes to immunity and boosting our natural anti-inflammatory response to disease and infections. In a study into the effects of fungus (yes it sounds gross but that is what mushrooms are), researchers found "immuno-modulatory and/or antitumor activity have been isolated from mushrooms." this means mushrooms may have the power to fight off both invaders and growing cancer cells.

Mushrooms contain zinc, selenium and B vitamins, all of which help support immunity. "The major immunomodulating effects of these active substances derived from mushrooms include mitogenicity and activation of immune cells, such as hematopoietic stem cells, lymphocytes, macrophages, dendritic cells (DCs) and natural killer (NK) cells, resulting in the production of cytokines. The therapeutic effects of mushrooms, such as anticancer activity, suppression of autoimmune diseases, and allergy have been associated in many cases with their immunomodulating effects," the authors wrote.

Eating white "button mushrooms" has been shown to boost immunity, according to researchers who found that white button mushrooms may promote immune function by "increasing the production of antiviral and other proteins that are released by cells while seeking to protect and repair tissue." So while they are out looking for cancer cells these immune cells will destroy anything that doesn't look familiar, including viruses.

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8. Carrots for beta carotene, which converts to vitamin A in the body

Beta carotene is one of the "server" antioxidants that helps your body convert it into vitamin A, which is a vital nutrient for cell growth and in supporting your vision, heart, lungs, and kidney function. A large carrot contains six milligrams of beta carotene in one large carrot -- enough to convert to 1,000 mcg of vitamin A.

Drinking 16 ounces of carrot juice a day for three months helped to significantly increase the total antioxidant status in the body, one study showed, and lowered markers for inflammation and heart disease, including lowering blood pressure. Carrot seeds and extract have been studied and shown to have powerful anti-bacterial and anti-fungal properties. Carrot seed extract has been shown to lower inflammation and provide wound-healing benefits.

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9. Garlic for allicin and to fight inflammation

There's a reason that garlic has been widely used in cooking for centuries, since it lowers inflammation, raises immunity, and kills many of the bacterial invaders that could be lurking in food and cause you problems, according to studies. "Garlic has been used for centuries in various societies to combat infectious disease," the research authors noted. "Historically, it is believed that Louis Pasteur described the antibacterial effect of garlic in 1858 for the first time, although no reference is available.

More recently, garlic has been proven to be effective against Salmonella, E-coli and even fight dental plaque, the authors wrote. All of the antibacterial activity of garlic is due to the fact that it contains allicin, a compound that gets released when garlic is chopped or chewed. Allicin has been shown to reduce inflammation and have antioxidant benefits.

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10.Turmeric to fight inflammation and infection

Turmeric has been used for centuries as a way to fight off infection and inflammation, and in recent studies, the powerful spice (which contains curcumin) has been shown to equip the immune cells with the ammo they need.

Specifically, one review of the research on curcumin states: "Traditionally known for its anti-inflammatory effects, curcumin has been shown in the last two decades to be a potent immunomodulatory agent that can modulate the activation of T cells, B cells, macrophages, neutrophils, natural killer cells, and dendritic cells."

In other words, if you're equipping these cells, you want curcumin in your arsenal. Curcumin's many benefits "might be due in part to its ability to modulate the immune system," the authors note. "Together, these findings warrant further consideration of curcumin as a therapy for immune disorders."

Bottom Line: Eat more fruits and vegetables to equip your immune cells with the nutrients they need to fight off bacterial and viral invaders and keep inflammation low. By eating a diet high in plant-based foods and low in inflammatory foods like meat and processed foods, you can support a healthy immune system, that will support you back.