Every winter, as temperatures drop lower, your chances of getting sick climb higher. According to research from the Centers For Disease Control, in one sample year, nearly 14% of adults got a cold in October through December, while just 7% did in July to September.
“Winter really is the season of giving and, unfortunately for us, this often includes a microscopic gift, like a virus or bacteria,” says Lifeforce Clinician Vanessa Clark, PA-C, RDN.
Clark notes that viruses are believed to replicate more rapidly in colder weather, which coincides with a reduced function of our cilia — the hairs lining our upper respiratory tract that are tasked with sweeping pathogens out of our system.
Environmental factors can also leave us in the cold. “In the winter months, we are exposed to less sunlight, more indoor time, and more circulating viral illness, which can make our immune system more vulnerable to threats,” warns Lifeforce Clinician Barbara Dougherty, MSN, CRNP.
One of our leading defenders is our diet. In fact, certain foods have science-backed, immune-boosting benefits, while others can impair immunity. This is food for thought, especially this season. “With greater energy and nutrient needs, and less natural vitamin D production, it is much more crucial to stick to a healthy diet as the weather gets chilly,” Dougherty says.
We’ll show you how. Our experts dish on 12 foods that support a healthy immune system.
Immunity 101
First, a quick explainer on immunity. Our immune system is made up of two distinct parts — the innate and the acquired immune system. Clark says, “The innate system is the components we are born with — the organs, tissues, and proteins that make up our immune system, like our tonsils, adenoids, lymph nodes, bone marrow, and spleen, and the proteins or components these systems form, such as white blood cells. Our acquired immune system is the part that creates antibodies in response to a microbial exposure, whether through vaccines or illness.”
Together, these systems are responsible for defending our bodies from invading illnesses. “Our immune system is both the physical barrier to invaders as well as the cellular components and messengers, acting like soldiers, that attack foreign invaders,” Clark explains. “In order to optimize immune function, we need to give our body not only the nutrients it needs to build a strong fortress, but also the ability to enact a swift and mobile response if it does come in contact with a fungus, virus, or bacteria.”
The Diet/Immunity Connection
Food gives us the raw ingredients to defend immunity. Some foods deliver compounds that have anti-inflammatory, antimicrobial, antioxidant, and immune-boosting effects.
Managing inflammation is especially important for immunity. “Inflammation is actually a necessary part of fighting off germs,” Clark explains. “What we don't want is for this inflammation to become prolonged (chronic) or systemic. Inflammation is very much about just the right amount and for just the right amount of time. Enough to fight off the bugs, but not enough to send our whole bodies into chaos. This is where your diet comes in. A diet rich in antioxidants and anti-inflammatory compounds can help improve the body's killing capacity by neutralizing free radicals during the fight, but also by tamping down the inflammation when the infection is cleared to then give your body a chance to recover and restore balance.”
12 Foods to Boost Your Immune System
So, which foods provide these powers? The truth is, “there is no one magic food that ultimately defends you against any virus or bacteria,” says Lifeforce Clinician Johanna Lancaster, a Functional Medicine Nurse Practitioner. Instead, the best strategy against sickness is an overall balanced diet full of whole, unprocessed foods.
“A diet rich in whole grains, fruits, vegetables, nuts, seeds, and lean protein will provide most of the key building blocks of a healthy immune system,” Clark adds.
While they’re not magic, these 12 foods are scientifically shown to help bolster immunity.
1. Yellow peppers.
“Vitamin C has been a standout in the immunity world for a long time,” Clark says. It earned its rep for good reason: vitamin C may help reduce the duration and severity of a cold by improving the response of white blood cells — our main defense cells — to a virus, Clark explains. In trial research, vitamin C helped reduce the duration of a cold by about 8%. “Eating more yellow peppers is a very efficient way of upping your vitamin C intake,” Clark suggests. “One large yellow pepper contains about 342 mg of vitamin C. That's 380% of the recommended daily intake!”
2. Citrus fruits.
Fruits like lemons, oranges, and limes are also standout sources of vitamin C. Lancaster recommends, “Use citrus juices to make salad dressings, and add a splash to season food or flavor water.”
3. Mushrooms.
Shrooms like shitake, maitake, and reishi are a good source of beta glucans, which have been shown to modulate our gut health and immune system, Dougherty says. “Beta glucans are polysaccharides — naturally occurring sugars — that can activate immune cells to help fight infection and support our overall health in the winter months.”
4. Ginger.
“Ginger contains antimicrobial and anti-inflammatory compounds, which may enhance the activity of immune cells,” Dougherty says. “We can incorporate ginger into our diet by using fresh ginger in soups and baked goods. Ginger tea or adding a slice of ginger to your water is an easy way to reap the benefits for immune health.”
5. Garlic.
“Garlic might keep more than just vampires away; it can also help keep viruses at bay,” Clark says. In a randomized trial, garlic reduced the incidence of colds. Garlic may also lessen the duration and severity of viruses, thanks to the direct antimicrobial and antiviral properties of its sulfur-containing compounds, particularly allicin. Clark explains that these compounds help improve the response of white blood cells when they’re mobilized to fight pathogens.
6. Leafy greens.
Leave it to leafy greens to improve your immune response. “Spinach and kale contain several beneficial immune boosting compounds, including flavonoids, carotenoids like beta-carotene, Vitamin C, and Vitamin E,” Clark explains. “Flavonoids may help decrease the likelihood of getting sick, particularly from upper respiratory tract infections. Carotenoids exert an anti-inflammatory response in the body. Vitamins C and E have known anti-inflammatory properties and are important in regulating and modulating immune system responses. Greens also contain zinc, which has been shown to help reduce incidence and severity of colds.”
7. Purple sweet potato.
These bright spuds contain polysaccharides that are known to activate the immune system to reduce inflammatory processes and fight sickness, according to Lancaster. “They support immune cells in the gut, increase beneficial gut bacteria, and support intestinal barrier function,” says Lancaster.
8. Turmeric.
“This spice is rich in a particular polyphenol called curcumin. Curcumin is the workhorse behind the anti-inflammatory properties often attributed to turmeric,” Clark says. She notes that the body absorbs curcumin better when it's paired with piperine, an alkaloid in black pepper. Sprinkle black pepper into dishes with turmeric to boost its benefits, help reduce inflammation, and support a healthy immune system.
9. Greek yogurt and kefir.
In addition to immune boosting vitamin D, Greek yogurt contains beneficial probiotics and good bacteria to support gut health, Dougherty says. “Since an estimated 70% of our immune system is located in our gut, it is important that we eat foods that feed our microbiome with both prebiotic and probiotic properties such as fiber and fermented foods.” Try mixing Greek yogurt with berries for extra fiber. Dougherty recommends choosing 2% or full fat yogurt with live and active cultures and no added sugar. Bonus: “This also helps us meet our protein and healthy fat macros!”
Clark is also a fan of kefir’s probiotic punch. “Due to its lower lactose content, it tends to be better tolerated by people with lactose intolerance as compared to yogurt,” she says. She also notes that kefir, yogurt, and fermented vegetables have direct antiviral properties.
10. Cranberry.
Another berry good pick for gut health. According to Lancaster, cranberries are rich in polyphenols, flavonoids, and agavins — antioxidant- and prebiotic-packed compounds that support mucosal immune modulation in the gut and a diverse healthy microbiome. “Cranberries are also rich in proanthocyanidins, a compound that supports white blood cell function,” she says. “With holidays around the corner, try out some delicious, low-sugar cranberry recipes.”
11. Broccoli.
When we chew cruciferous vegetables like broccoli, cauliflower, and broccoli sprouts, it releases a chemical called sulforaphane, which helps increase antioxidant and glutathione production. “Glutathione is a very powerful antioxidant and acts as an immune system modulator,” Clark says. “It does this by helping to maintain normal levels of cytokines, increasing the number of T cells, and supporting mast cell function.”
12. Green tea.
“Tea can be a significant contributor to your immune arsenal,” Clark says. “It provides both hydration and beneficial phytonutrients that can be significant contributors to the overall functioning of your immune system. Green tea especially tends to be a standout in this department.” That’s because green tea is particularly high in an antioxidant called epigallocatechin gallate (EGCG), which helps eliminate free radicals, preventing them from damaging healthy cells and tissues. The soothing sip also delivers L-theanine, which helps boost immune function and reduce inflammation, perhaps in part by reducing cortisol levels.
Foods to Watch Out For
Just as there are foods that strengthen the immune system, there are others that weaken it. “In addition to maximizing immune boosting foods, try to minimize foods that promote inflammation, such as added sugars, refined grains, saturated fat, and ultra-processed foods,” Clark notes. “Now is a good time to start thinking about strategies to curb our intake of some of these common pro-inflammatory foods that are so often on our dinner tables and breakroom tables this time of year.”
While none of us are immune to temptation, Clark suggests some simple tips to stay on track. “You can bring a healthy dish like a side salad to a potluck or refrain from taking leftovers home,” she says. “Share your goals or intentions with others close to you and be clear if you do not want holiday cookies, breads, pies, etc. as a gift.”
Dougherty recommends having healthy snacks readily available at holiday festivities and eating a nourishing meal and hydrating before parties. “These tactics can help us stay healthy, improve our immune health, and avoid illness during the winter holidays!”
The gift of a healthy holiday season will truly keep on giving.
This article was medically reviewed by:
Barbara Dougherty, APRN, FNP-BC
Vanessa Clark, PA-C, RDN