Flu season is here, and everyone is looking for ways to boost their immune system. But with so much information out there, how do you know which nutrition advice actually works? As a dietitian, I want to help you understand the role that specific nutrients play in immune health—what’s truly evidence-based, and what might be more conjecture or a little overhyped. Here's an overview of what really works for supporting your immune system, with a focus on flu season.

Australia's 2024 winter flu season peaked later in the year and lasted longer than in 2023, according to new data from the National Notifiable Disease Surveillance System. With this extended flu season, keeping your immune system strong has become more important than ever to help prevent and combat illness effectively.

Nutrients Proven to Support Immune Health

1. Vitamin C: A Supportive Ally, Not a Cure-All

Vitamin C is one of the most popular nutrients for immune health, and it does have some benefits. Regular vitamin C intake might reduce the duration of colds, especially for people under physical stress like athletes. However, the evidence doesn't show that it will prevent colds or flu for most people. Sources like citrus fruits, strawberries, and bell peppers are great for meeting your vitamin C needs.

Bottom Line: Vitamin C may help shorten the duration of a cold, but it's not a magic bullet for prevention. The benefit is modest but still worth including as part of a balanced diet.

2. Vitamin D: More Than Just the Sunshine Vitamin

Vitamin D is crucial for regulating immune responses. During the winter months, when sunlight exposure is limited, many people experience Vitamin D deficiency, which can weaken the immune system. Studies suggest that people with adequate levels are less likely to experience respiratory infections, and those with a deficiency may benefit the most from supplementation.

Bottom Line: Maintaining adequate Vitamin D levels is essential for immune health. If you are deficient, consider supplementation, especially during the winter months.

3. Zinc: Timing Is Everything

Zinc is another essential mineral that plays a key role in immune health. Research shows that taking zinc within the first 24 hours of cold symptoms might help reduce the duration of a cold. However, caution is needed with the dosage—too much zinc can lead to side effects like nausea and can interfere with other nutrients.

Bottom Line: Zinc can help reduce the duration of cold symptoms if taken early, but be mindful not to overdo it. Focus on dietary sources like shellfish, beans, and nuts to ensure you're getting enough.

4. Probiotics: Supporting Your Gut, Supporting Your Immune System

The connection between gut health and immune function is well-established. Specific strains of probiotics, such as Lactobacillus and Bifidobacterium, have been shown to help support immune health and may reduce the risk of respiratory infections. However, not all probiotics are the same, and effectiveness depends on the strain and individual response.

Bottom Line: Probiotics can support immune health, but their effectiveness depends on the strain and individual factors. Foods like yogurt, kefir, and fermented vegetables are good sources to include.

5. Protein: Building Blocks of Immune Cells

Adequate protein intake is necessary for the production of antibodies and immune cells. A lack of protein can impair immune function, especially in those who are elderly or have other health conditions. Protein-rich foods like lean meats, legumes, dairy products, and nuts should be a staple in your diet to support immunity.

Bottom Line: Ensure you're getting enough high-quality protein daily to support immune health. Aim for a balanced intake from a variety of sources.

What to Avoid or Limit During Flu Season

Refined Sugar:

High sugar intake is linked to chronic inflammation, which may weaken immune responses over time. Although the evidence linking sugar directly to impaired acute immune function during an infection is still inconclusive, it makes sense to limit refined sugars and focus on nutrient-rich foods.

Bottom Line: Reducing sugar is always a good idea for overall health, but there's limited direct evidence of its role in short-term immune suppression.

Alcohol:

Excessive alcohol can impair immune function and disrupt sleep, both of which are crucial for staying healthy. Alcohol should be consumed in moderation or avoided if you are trying to support your immune system during flu season.

Bottom Line: Limit alcohol to maintain strong immune function. Focus on staying hydrated with water or herbal teas instead.

Hydration and the Importance of Fluids

Hydration Works:

Staying well-hydrated helps maintain mucous membrane health, which is important for trapping pathogens and reducing the risk of infection. Warm fluids like broth-based soups and herbal teas can also be comforting if you have the flu. The "chicken soup effect" might not cure the flu, but it helps with hydration, and the warmth can soothe symptoms.

Bottom Line: Proper hydration is key during flu season. Keep your fluids up with water, herbal teas, and broth.

Managing the Flu with Nutrition

If you find yourself coming down with the flu, here are some nutrition strategies to help support your recovery:

1. Warm, Easy-to-Digest Foods:

When you're sick, focus on foods that are easy on the digestive system, like soups, broths, and herbal teas. Adding ginger and garlic can provide some anti-inflammatory benefits, though these foods should be considered supportive rather than curative.

2. Vitamin C and Zinc:

Once symptoms start, consider moderate vitamin C and zinc supplementation. While neither will cure the flu, they may reduce symptom duration if taken early. Stick to moderate doses to avoid side effects like digestive upset.

3. Avoid Heavy, Greasy Foods:

During illness, it's best to avoid heavy, greasy foods, which can be harder to digest and contribute to discomfort. Stick with light and balanced meals, and focus on maintaining hydration.

4. Herbal Teas :

Herbal teas like chamomile or peppermint may help ease symptoms such as sore throat and aid relaxation.

What is not well-supported by evidence?

“Superfoods” Like Turmeric or Kombucha:

While foods like turmeric and kombucha have their benefits—such as anti-inflammatory properties and gut health support—they are not a cure for the flu. Including these in your diet can be part of a supportive approach to overall health, but it is essential to set realistic expectations.

Bottom Line: Turmeric and kombucha may support general health, but they are not treatments for the flu. Use them as complementary parts of a balanced diet.

Mega-Dosing Vitamin C:

Taking extremely high doses of vitamin C (over 2000 mg/day) has not been proven to prevent the flu, and can lead to side effects such as diarrhoea. It's best to stick to moderate supplementation or dietary sources.

Bottom Line: Mega-dosing vitamin C isn't necessary and could cause more harm than good. Moderate intake may help during illness, but more is not always better.

Conclusion

A well-balanced diet rich in vitamin C, D, zinc, protein, and probiotics is the best strategy for supporting immune health during flu season. With Australia's 2024 winter flu season peaking later and lasting longer, it's more important than ever to take proactive steps to support your immune system.

While no single food or nutrient can guarantee you won't catch the flu, supporting your immune system with the right nutrients can certainly improve your body's ability to defend itself and recover faster.

Remember, stay hydrated, limit refined sugars, and consume alcohol in moderation to keep your immune system functioning at its best. And if you do catch the flu, rely on broths, light meals, and good hydration to support your recovery.

Disclaimer: This article is for informational purposes only and does not replace professional medical advice. Always consult with your healthcare provider before making any significant dietary changes or starting new supplements.

Summary: Boosting Your Immune System with Nutrition During Flu Season

As flu season stretches longer in Australia this year, it's more important than ever to boost your immune system. A balanced diet rich in vitamin C, D, zinc, protein, and probiotics can effectively support your immune health.

• Vitamin C may help shorten the duration of colds, but it's not a magic bullet for prevention. Include sources like citrus fruits (lemon, lime, oranges), capsicum and kiwi fruit ideally.

• Vitamin D helps regulate immune responses, especially for those deficient—consider supplementation during winter.

• Zinc can reduce the duration of cold symptoms if taken early but must be used in moderation.

• Probiotics support gut health, which is linked to immunity, though effectiveness varies by strain.

• Having adequate dietary fibre and fluids (e.g. oats, seeded bread, psyllium husk) is the cornerstone of a healthy gut microbiome and is likely more beneficial than probiotics but you could do both.

• Protein is crucial for producing antibodies and immune cells, so ensure enough daily intake from sources like lean meats and legumes.

Avoid refined sugars and limit alcohol to reduce inflammation. Stay well-hydrated with water and herbal teas to maintain mucous membrane health. If you do catch the flu, focus on easy-to-digest foods, adequate rest, and light meals to support recovery.