Winter Nutrition and Supplements for Immune Support

As the temperatures drop, our bodies face unique challenges during the winter months. Colder weather, limited sunlight, and the prevalence of seasonal illnesses can impact our immune systems, potentially leaving us more vulnerable to colds, flu, and other infections. Fortunately, proper nutrition and supplements play a crucial role in supporting immune health during this time of year. Maintaining healthy habits can serve as a stepping stone to increased energy, disease prevention, and improved mood, to name a few. 

Immune System¹

Our immune system is highly effective in protecting the body from pathogenic microorganisms. However, pathogens can still successfully bypass these defenses, leading to illness. Questions remain regarding whether specific interventions, such as dietary modifications, supplementation with specific vitamins or herbal compounds, or other lifestyle adjustments, could optimize immune function. As a whole, the immune system is quite complex, and researchers are still investigating the various interactions within the body. For now, limited evidence-based studies exist proving a direct link from lifestyle modifications and boosting the immune system. However, this does not diminish the significance of studying the impact of lifestyle factors on immune system function. Adopting these strategies is prudent, as they are likely to support immune function and confer additional, well-documented health benefits. 

The Role of Nutrition in Immune Function

Nutrition is fundamental to maintaining a well-functioning immune system. Specific vitamins, minerals, and bioactive compounds support the various processes that contribute to immune defense. Consuming adequate amounts of several vitamins and minerals—including vitamin C, vitamin D, zinc, and probiotics—is important for proper immune function, and clinical deficiencies of these nutrients weaken immunity and can increase susceptibility to infections. 

Evidence-Based Key Nutrients for Immune Health

Vitamin C: Vitamin C, also known as ascorbic acid, is a water-soluble antioxidant that is widely recognized for its role in immune defense.² It is a crucial component to support blood vessel, cartilage, muscle, and collage formation. It also supports various immune functions, including the activation and proliferation of white blood cells, and enhances the skin’s ability to act as a barrier to pathogens. While vitamin C does not prevent colds, it has been shown to reduce the duration and severity of cold symptoms.

• Scientific Evidence: A meta-analysis published in Cochrane Database of Systematic Reviews demonstrated that regular vitamin C supplementation (1-2 grams per day) reduces the duration of common cold symptoms by approximately 8% in adults and 14% in children.³ In addition, vitamin C supplementation may reduce the severity of symptoms such as fever, cough, and nasal discharge.
• Sources: Citrus fruits (oranges, grapefruits), strawberries, kiwi, bell peppers, and broccoli.
• Supplementation: The RDA for vitamin C is 15 to 115 mg for infants and children, depending on age, and 75 to 120 mg for nonsmoking adults, including those who are pregnant or lactating; people who smoke need 35 mg more per day.⁴

Vitamin D: Vitamin D plays a pivotal role in immune modulation. It is involved in the activation of immune cells such as T-cells and macrophages, which are crucial for the body’s defense against pathogens.⁵ Vitamin D deficiency affects the body’s susceptibility to infection, partly by weakening tissue barriers, and it has been associated with an increased risk of influenza and other respiratory tract infections, hepatitis C, HIV, and other viral infections. It also impairs macrophage function and interleukin-10 production.

• Vitamin D exists in two forms: vitamin D2 and vitamin D3. It is biologically inert until it undergoes two hydroxylations in the body for activation. The first hydroxylation, which occurs in the liver, converts vitamin D to 25-hydroxyvitamin D [25(OH)D]. The second hydroxylation occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D]. The body can also synthesize vitamin D as a result of sun exposure. 
• Scientific Evidence: A systematic review published in The Lancet Diabetes & Endocrinology concluded that vitamin D supplementation significantly reduces the risk of acute respiratory infections, particularly in individuals with low baseline vitamin D levels.⁶ This is especially relevant during the winter months when sunlight exposure is limited and the body’s ability to synthesize vitamin D from sunlight is reduced.
• Sources: Fatty fish (e.g., salmon, mackerel), fortified dairy products, egg yolks, beef liver, cheese, and fish liver oils. 
• Supplementation: The RDA for vitamin D is 10 to 15 mcg (400 IU to 600 IU) for children, depending on age, and 15 to 20 mcg (600 to 800 IU) for adults, including those who are pregnant or lactating.⁷ 

Zinc: Zinc is an essential trace mineral that is involved in numerous aspects of immune function, including cell signaling, inflammation regulation, and the production of white blood cells.⁸ Zinc has been found to play a role in both innate and adaptive immunity, helping the body to mount a response to infections.

• Scientific Evidence: A 2021 systematic review and meta-analysis found that zinc appears to reduce the duration of the common cold but has mixed effects on the severity of signs and symptoms.⁸ In participants who used products containing zinc, symptoms resolved an average of 2 days earlier than in those who took a placebo. Zinc also reduced the severity of symptoms on the third day of illness. However, average daily symptom severity did not differ between those who were and were not treated with zinc supplements. In addition, zinc did not affect the risk of developing a cold after rhinovirus inoculation.
• Sources: Meat, shellfish, legumes, seeds, nuts, and whole grains.
• Supplementation: The RDA for zinc is 2–13 mg for infants and children, depending on age, and 8–12 mg for adults, including those who are pregnant or lactating.⁹

Probiotics: Probiotics are live microorganisms that confer health benefits when consumed in adequate amounts. They play a critical role in maintaining gut health, which is intrinsically linked to immune function.¹⁰ Approximately 70% of the body’s immune cells reside in the gut, highlighting the importance of a healthy microbiome for effective immune defense.

• Scientific Evidence: A randomized controlled trial published in Frontiers in Microbiology demonstrated that probiotics, particularly strains like Lactobacillus and Bifidobacterium, can reduce the incidence and duration of upper respiratory tract infections in both adults and children. Probiotics enhance mucosal immunity by increasing the production of immunoglobulin A (IgA), an antibody that helps protect mucosal surfaces such as the respiratory tract.
• Sources: Fermented foods such as yogurt, kefir, sauerkraut, kimchi, and miso.
• Supplementation: Although there are no current guidelines surrounding recommended dosing for immune function, probiotics are measured in colony forming units (CFU), which indicate the number of viable cells.⁵ Amounts may be written on product labels as, for example, 1 x 10⁹ for 1 billion CFU or 1 x 10¹⁰ for 10 billion CFU. Many probiotic supplements contain 1 to 10 billion CFU per dose, but some products contain up to 50 billion CFU or more. However, higher CFU counts do not necessarily improve the product’s health effects.

Other Healthy Ways to Strengthen the Immune System¹

• Don't smoke.
• Eat a diet high in fruits and vegetables.
• Exercise regularly.
• Maintain a healthy weight.
• If you drink alcohol, drink only in moderation.
• Get adequate sleep.
• Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly.
• Try to minimize stress.
• Keep current with all recommended vaccines. Vaccines prime your immune system to fight off infections before they take hold in your body.

Considerations for Supplement Use

While supplements can be beneficial, it is important to use them judiciously. Excessive intake of certain nutrients can lead to toxicity and adverse health effects. Furthermore, certain supplements may interact with medications or underlying conditions. Below are a few crucial tips to consider before starting any supplement. 

• Consult with a healthcare professional or pharmacist before starting any new supplement regimen. 
• Balance supplementation with food sources to ensure a holistic approach to nutrition.
• Be mindful of possible interactions between supplements and medications.

Conclusion

Although the winter season can increase risk for infections, taking proactive steps to maintain a healthy lifestyle can help prevent diseases, maintain high energy, and improve mood. Specifically, vitamin C, vitamin D, zinc, and probiotics are among the most commonly-studied supplements found in our diet that can support immune health. Along with a balanced diet rich in fruits, vegetables, and whole grains, these strategies can offer a holistic approach to wellbeing. Always consult with a healthcare professional before introducing new supplements, especially if you have preexisting conditions or take other medications.

References: 

1. Harvard Health Publishing. How to boost your immune system - Harvard Health. Harvard Health. Published February 15, 2021. https://www.health.harvard.edu/staying-healthy/how-to-boost-your-immune-system. 
2. Mayo Clinic . Vitamin C. Mayo Clinic. Published August 10, 2023. https://www.mayoclinic.org/drugs-supplements-vitamin-c/art-20363932. 
3. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;2013(1):CD000980. Published 2013 Jan 31. doi:10.1002/14651858.CD000980.pub4. 
4. Office of Dietary Supplements - Vitamin C. ods.od.nih.gov. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/#h2. 
5. National Institutes of Health. Office of Dietary Supplements - Dietary Supplements for Immune Function and Infectious Diseases. ods.od.nih.gov. Published June 27, 2023. https://ods.od.nih.gov/factsheets/ImmuneFunction-HealthProfessional/. 
6. ‌Jolliffe DA, Camargo CA Jr, Sluyter JD, et al. Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials. Lancet Diabetes Endocrinol. 2021;9(5):276-292. doi:10.1016/S2213-8587(21)00051-6.
7. Office of Dietary Supplements - Vitamin D. ods.od.nih.gov. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/#h2. 
8. Hunter J, Arentz S, Goldenberg J, et al. Zinc for the prevention or treatment of acute viral respiratory tract infections in adults: a rapid systematic review and meta-analysis of randomised controlled trials. BMJ Open. 2021;11(11):e047474. Published 2021 Nov 2. doi:10.1136/bmjopen-2020-047474. 
9. Office of Dietary Supplements - Zinc. Nih.gov. Published 2017. https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/#h2. 
10. Wiertsema SP, van Bergenhenegouwen J, Garssen J, Knippels LMJ. The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies. Nutrients. 2021;13(3):886. Published 2021 Mar 9. doi:10.3390/nu13030886.

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