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10 Dietitian-Approved Immune Boosters for Flu Season

Flu season has been out of hand this year. My usual strong immune system has been put to the test. Part of that change is having a toddler; kids seem to share germs better than anyone. Part of that is being so busy working on my forthcoming book, Real Food for Pregnancy, that I haven’t had as much downtime as I should.

I’ve had to rely heavily on my arsenal of natural remedies and nutritional strategies to fight this off. If you have the flu, remember that it’s a virus, so it will take some time to get better (the strain I got really seems to linger), but you can still use nutritional strategies to support your overall immune response.

Whether you’re suffering with the flu or want to avoid getting it (or at least try), I’ve compiled 10 dietitian-approved immune boosters for flu season.


10 Dietitian-Approved Immune Boosters for Flu Season

1. Ditch Sugar

It’s no secret that sugar is not a health food. In day-to-day life, I hope that you keep your intake minimal, but when you have even the tiniest inkling that you’re getting sick, I encourage you to go full stop.


Sugar suppresses the immune system and is the last thing you want to ingest while sick. I know a lot of people want comforting foods when they’re sick, but eating ice cream or cookies at this time is doing the opposite of what your body needs.

The rare exception I make to this is if I have a really bad cough or sore throat. In that case, I may eventually decide to have cough drops or some lemon-honey tea (fresh-squeezed lemon and raw honey in hot water… and maybe a little fresh-grated ginger).

Otherwise, I’m militantly anti-sugar until I’m 100% back to myself (meaning I wait several days with no cold or flu-like symptoms before indulging). Then you may or may not see some super dark chocolate sneak back in. 😉

2. Eat Less Dairy (at least temporarily)

Have you ever monitored your symptoms after eating dairy products? For some people, dairy products thicken mucus or lead to clogged sinuses. If this is you, try leaving dairy out of your diet at the first sign of symptoms (as you would do with sugar).

While I’ve never seen any “hardcore” scientific data to link dairy intake and mucus production, it’s a common school of thought in naturopathic medicine. For me, I observe a distinct difference in mucus and sinus congestion, so I opt to leave it out.

Next time you’re feeling under the weather, and especially if your symptoms include congestion, sinus pressure, or a productive cough, try going dairy-free and see if it makes a difference.

3. Bone Broth

Grandma’s chicken soup is a comfort food for a reason. Warm broths help loosen mucus and soothe a sore throat; they provide electrolytes to help you stay hydrated; and they have specific amino acids that feed the cells that line your gut. Since approximately 80% of your immune system is located in your gut, anything and everything you can do to keep your gut happy is worth doing.

It’s simple: support the gut, support the immune system.

If you’ve never made bone broth, check out my recipe. I now make bone broth in my Instant Pot, an electric pressure cooker, that gets the job done in 90 minutes or less.

You can drink broth on it’s own or make it into a soup. If drinking plain, you’ll need to season it up—some salt, coconut aminos, and a squeeze of lemon or lime juice is excellent. I mostly opt for making it into a full-on soup. I just make a batch of Carrot Ginger Squash Soup this weekend and it was incredibly soothing to my throat.

If you’re not into broth or want additional immune/gut support, you can incorporate gelatin or collagen protein powder into your diet. I like adding a tablespoon of collagen to my tea in the morning. For a treat that’s low in sugar and super nourishing, try my Tart Cherry Gummies.

4. Fermented Foods

Fermented foods are full of naturally-occurring, healthy bacteria (probiotics) that play a fundamental role in your immune system. Recent research has highlighted the ways that probiotics can impact the function of a variety of immune cells including: dendritic cells, epithelial cells, T regulatory cells, effector lymphocytes, natural killer T cells, and B cells. (Immunological Reviews, 2017)

While scientists work out the details and exact mechanisms behind the immune benefits, you can nosh on some kimchi and fermented veggies to experience the benefits firsthand.

Most people assume that supplements are always superior to foods when it comes to probiotics, but that’s not always true.

Many fermented foods contain probiotic counts far higher than most supplements.

For reference, probiotic supplements are measured in the number of colony forming units (CFUs) and provide anywhere from a few million to tens of billions of bacteria per serving. If you examine sauerkraut, yogurt, and kefir, they contain bacteria counts in the trillions in just a single tablespoon. For the research on fermented foods and their levels of probiotics, see this post.

If you notice congestion or worsening of symptoms when eating dairy, steer clear of yogurt and kefir, and instead opt for kimchi, sauerkraut, lacto-fermented veggies (like these fermented carrots with ginger and jalapeno), kombucha (choose one that’s low in sugar), or miso soup.

I’m certainly not opposed to probiotic supplements, but fermented foods should not be discounted as being “weaker” or less effective.

5. Vitamin D

Ever notice how cold and flu season coincides with the time of year that offers the least amount of sun exposure? Some researchers suggest that this is not a coincidence. In the winter months, vitamin D levels take a seasonal dip and our immune systems are more vulnerable to infections. Vitamin D plays a very important role in your overall immune response. A recent meta-analysis of 25 randomized controlled trials (read: big, well-designed study) found that vitamin D supplementation protected against acute respiratory tract infections. (BMJ, 2017)

Vitamin D also appears to “dampen the damaging effect of cell stress response and of the immune reaction,” meaning it allows your body to fight off an infection without too much collateral damage. (Clinical Therapeutics, 2017)

Where you live can help predict your risk for vitamin D deficiency. If you live above 33 degrees latitude north (or below 33 degrees latitude south), it’s physically impossible to make vitamin D from sun exposure for a portion of the year. The further you go north (or south, if you live in other hemisphere), the longer that time period extends. So, if you’re in Boston, you won’t be able to make any vitamin D from late fall to early spring (if you happen to get a day warm enough to bare any skin!).

->>> For more on this topic, see this evidence-based article to learn 10 things you didn’t know about vitamin D.

Before we move on, please take a moment to read the above article. Newer research suggests that vitamin D recommendations are incorrect and have woefully underestimated the body’s need for vitamin D (by a factor of 10).

Diet plays a very small role in meeting your vitamin D needs and without sun exposure to help you out, that leaves you with supplements to carry you through the winter months (outside of certain vitamin D UV lights/tanning beds). In other words, I highly encourage a vitamin D supplement in the winter months unless you live in a warm, sunny, southern (meaning equatorial) climate. The above linked article talks more about dosing, lab testing to determine if you’re deficient, and more.

6. Vitamin C

This powerhouse of an antioxidant is widely recognized for its role in immune health. Found in citrus fruit, broccoli, bell peppers, and many other kinds of fresh produce, vitamin C improves the function of neutrophils (white blood cells), which play a key role in fighting off pathogens.

Studies have shown that neutrophil activity is optimized with vitamin C intakes of at least 250 mg/day. (Nutrients, 2017)

I usually take ~1,000 mg/day when fighting off an infection and certainly higher doses are ok (some get diarrhea with high doses, so beware).

I also tend to prioritize high-vitamin C foods, such as grapefruit, lemon juice in water, broccoli (not overcooked), and rose hip tea. (Pro tip: the white pith of citrus fruits is more concentrated in vitamin C than the flesh. Yes, it’s bitter, but it’s good for you!)

Vitamin C-rich foods also come packed with complementary nutrients that may be beneficial, like bioflavonoids, which may not be present in supplements. Think food first, but feel free to add a supplement if needed.

7. Zinc

Referred to as a “gatekeeper to the immune system” by some researchers, zinc is required to maintain a normal immune response.

As one review article explains,

“Zinc ions are involved in regulating intracellular signaling pathways in innate and adaptive immune cells.” (Nutrients, 2017)

Your best dietary sources of zinc are red meat and oysters. All other meat, fish, and poultry are good sources as well.

Plant sources include whole grains, nuts, seeds, and legumes, however the presence of phytic acid and tannins significantly hinder zinc absorption from these foods. Due to the differences in bioavailability, vegetarians and vegans are at high risk for zinc deficiency; and recommended intakes for zinc are 1.8x higher for vegetarians to make up for this. (Pro tip: One way to enhance zinc absorption from plant foods is to soak, sprout, or ferment them before consuming. These Crispy Cashews are an example of this.)

If you don’t regularly consume these foods, a zinc supplement can be used, however be aware that long-term use can deplete the body of copper. A week or two of zinc supplementation is A-ok, but be careful with long term use. Food sources of zinc are naturally balanced in zinc:copper. (Nature is smart, right?!)

Vitamin A

Like so many other nutrients, vitamin A is involved in immune health and overall resistance to infections. Those with vitamin A deficiency face a significantly higher risk for multiple types of infections.

To enhance your immune response, consuming foods rich in preformed vitamin A is your best defense.

I specify “preformed” because vitamin A comes in many different forms in food; some forms require conversion inside your body to become metabolically active (carotenes), and others come in the already active “preformed” variety (retinols). Your ability to convert carotenes into retinol is partly determined by genetics, and a huge proportion of us lack the ability to do this conversion efficiently (if you want to nerd out, look up BCMO1 SNPs). Preformed vitamin A circumvents this problem entirely. (AJCN, 2010)

You find preformed vitamin A exclusively in animal foods, like liver (the #1 food source), butter, egg yolks, cod liver oil, and other fatty animal foods. (You’ll notice carrots and sweet potatoes aren’t on this list; they contain carotenes, not retinols. They’re great foods for other reasons, but unless you know your genetics, they’re not a reliable way to meet your vitamin A needs).

The other option is to take a vitamin A supplement, however large doses over a long period of time can result in toxicity, so I highly recommend working with a healthcare provider with extensive knowledge of nutrition before blindly supplementing.

9. Herbs

I keep an arsenal of herbs on hand in my home “farmacy.” From the mild support of herbal teas to the more targeted help of concentrated tinctures, herbs are extremely helpful in managing symptoms of colds and flus.

Although viral infections, like the flu, just have to “run their course,” some herbs have antiviral properties—like neem, olive leaf extract, and sambucus (black elderberry)—and as such, can be helpful when you’re battling the flu. Others are more general immune or adrenal support that just keep your stamina up for fighting off a lingering infection—echinacea, holy basil (tulsi), astragalus, and ashwaganda are some of my go-tos. Finally, I find it helpful to have some expectorants (aka: herbs that help you clear phlegm) to use as needed. Some examples are osha, usnea, and ginger. There are several dozen other immune-boosting herbs that I could list, but I’ll include some of my favorite combination formulas below.

I’m not big on taking pills, so I prefer herbal tinctures when possible. There are even some herbalists who believe that tasting the herb is an important part of its effects on the body. Whether that’s true or not, I’ll take that as an extra excuse to not force down horse pills.

The company Herb Pharm is one of my favorites. Their products are high-quality, reasonably priced, available OTC, and made with organic or wild-harvested herbs. Some products to check out:

Lung Expectorant
Rapid Immune Boost (used to be called Echinacea Goldenseal)

Safety note: I am comfortable using herbs after years of study (and both personal and professional use), but they are still powerful medicines, and as such, should be used under the guidance of a healthcare provider knowledgeable in herbs. This is especially important if you are pregnant or breastfeeding; not all are safe in these instances.

10. Sleep

Last, but certainly not least, sleep is absolutely essential to your immune health (and proper function of numerous other systems in your body). I’m sure you’ve had the experience of feeling like you’re somehow immune to the nasty bug going around the office, only to get up after a short/interrupted night of sleep to a sore throat or stuffy nose. Bad sleep has a huge carryover effect on your immune function.

As a mother to a young child, I know firsthand how precious sleep is (parents out there get it!). You really have to make an effort to turn out the lights early, disconnect from screens, and relax before you go to sleep. Whether that’s a cup of tea, a book, a bath, or something else, just do whatever you find necessary to get enough rest.

If you have trouble falling asleep, I encourage you to check out Yoga Nidra, also known as sleep yoga. There are countless recordings on YouTube that you can listen to while you lay in bed. If you fall asleep before the recording is up, even better.

And there you have it, 10 dietitian-approved immune boosters for flu season. Even if you incorporate only 2-3 of these into your daily life, your immune system will thank you.

Don’t underestimate the value of simple immune boosters to get you through flu season.

These are only 10 of my favorite natural immune boosters, but there are many others.

If you’ve found certain foods, nutrients, or habits helpful in fighting off the flu, please leave them in the comments below.

Until next week,

PS – To get a deeper understanding of several of the immune boosters in today’s post, read these articles:

10 Things You Didn’t Know About Vitamin D
5 Fermented Foods to Boost Your Intake of Probiotics
How to Make Bone Broth From Scratch

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Lily Nichols is a Registered Dietitian/Nutritionist, Certified Diabetes Educator, researcher, and author with a passion for evidence-based prenatal nutrition and exercise. Her work is known for being research-focused, thorough, and unapologetically critical of outdated dietary guidelines. She is the author of two bestselling books, Real Food for Pregnancy and Real Food for Gestational Diabetes.


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  1. Thanks for all the helpfull hints.
    Great to be reminded of all the things we should be taking timr to do in our busy lives.

    • You’re welcome, Ann. Hope you stay well this flu season!

  2. I’ve tried many different Vitamin D supplements. They always make me feel tired. The higher the dose, the more tired I feel. So tired I am unable to keep my eyes open. Have you ever heard of this before?

    • Hmm interesting. I’m not sure why that’s happening, Julie. Some possibilities: a sensitivity to an ingredient in vitamin D supplements (like the oil carrier), an issue with vitamin D metabolism (a genetic difference in your conversion of vitamin D), or maybe a matter of needing to consume/supplement with complementary nutrients involved in vitamin D metabolism (like magnesium, and others listed towards the end of this post). I’d suggest following up with a functional medicine practitioner to get to the bottom of this. Good luck.

  3. I am 70 and have never had a flu shot though I usually get a bad cold every winter which can last up to a month and could be the flu (not sure of the definition of flu) Anyway, I thought about how we call flu symptoms a cold and how we are much more likely to get a cold in Winter and though we endeavour to keep warm never as much as in Summer when we often get uncomfortably hot. I decided that when chilly for too long I would make sure I was uncomfortably hot for about half an hour to counteract it. By being conscientious I have avoided flu and colds for over a year. Last week I went to an alfresco restaurant and the evening was chilly. I developed quite pronounced cold symptoms and they lasted 3 days. However over that time I rugged up, got myself uncomfortably warm and VOILA ! no cold. Love to hear how this works for others.

  4. Great tips! Thanks so much for sharing! As a Mom of a 6 & 7 year old, I do my very best to eliminate as much sugar and dairy as possible especially during the so called “cold/flu season.” My husband and I have also eaten Juice Plus+ for 11 years (the research is pretty compelling) and our kiddos since birth. I took JP+ through both pregnancies and while nursing both. We very rarely get sick and if we do it is short lived. These tips and our daily JP+ have made a tremendous difference in our immune system’s ability to do its job among some other really incredible benefits! Again thanks for the great info!

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