Nutrition for Cold and Flu: Evidence-Based Strategies to Support Recovery

Nothing ruins momentum faster than waking up with a sore throat, blocked nose, and low energy.

And while nutrition isn’t a magic bullet, specific nutrients can indeed help support your immune response, potentially speeding up your recovery.

So, let's dive into exactly what you need to know, to bounce back faster.

First, Don’t Skip the Basics

Nutrition is important, but it won't replace essential recovery strategies. A strong immune system depends firstly on adequate sleep, managing stress, reducing training intensity, and good hygiene practices (e.g. food hygiene, regular handwashing, avoiding touching your face) (Gleeson, 2016).

Maintaining sufficient calories (particularly if you've been in a deficit) also ensures your body has enough energy available for immune support and recovery. So, if appetite permits, temporarily increasing calories towards maintenance levels during illness can help support immune function and recovery (Mountjoy et al., 2018).

And once you’ve nailed those fundamental recovery strategies, you might start looking into certain nutrients can give you an extra edge. However, instead of chasing every new supplement trend with limited or sketchy evidence, in this blog we're going to focus on Vitamin C, Zinc, Vitamin D, and Probiotics - the nutrients that have the strongest, most consistent support from recent and evolving research.

So, let’s dig into what the latest research actually says, how these nutrients could practically help, and how to use them to bounce back to full fitness faster.

Vitamin C: Not Just Old School Advice

Vitamin C (ascorbic acid) enhances immune function by boosting white blood cell activity, such as neutrophils and lymphocytes, and reducing inflammation through its antioxidant effects (Carr & Maggini, 2017).

For athletes and physically active individuals, maintaining regular vitamin C intake (~200 mg/day) is especially valuable, as intense training can temporarily weaken immunity (Hemilä & Chalker, 2013). This level, whether through diet or supplements, can reduce the duration of colds by about 8% in adults, roughly translating to half a day shorter symptoms - valuable when every training session counts (Hemilä & Chalker, 2013).

Supplementing with higher doses (500-1,000 mg/day) when symptoms first appear may slightly reduce cold severity or duration, though evidence is less consistent, and individual responses vary (Hemilä & Chalker, 2013; Abioye et al., 2023).

Dietary sources: Oranges (~70 mg), kiwis (~85 mg), strawberries (~85 mg per cup), bell peppers (~120 mg), broccoli (~80 mg per cup), spinach (~30 mg per cup), and kale (~80 mg per cup) are also practical ways to reach the 200 mg / day target.

Zinc: A Potential Edge When Used Early

Zinc plays a key role in immune health, with zinc ions blocking viral replication in the throat and nasal passages while boosting white blood cell activity (Hemilä, 2011). This makes it a popular choice for fighting colds, especially for active individuals keen to get back to training.

Research shows zinc lozenges, started within 24 hours of symptoms, may shorten colds by 1-2 days, though the 2024 Cochrane review flags the evidence as low-certainty due to study inconsistencies (Singh & Das, 2013; Nault et al., 2024). However, a high quality analysis of zinc acetate lozenges (80–92 mg/day) found a consistent 33% reduction (about 2-3 days), when used early, suggesting it’s still worth considering with the right approach (Hemilä, 2017).

Therapeutically, a dose of ~75 mg/day elemental zinc, split throughout the day, is practical and frequently used in studies showing benefits (Hemilä, 2017). However, also note, while it could trim days off your cold, side effects like metallic taste issues or nausea are something to consider. 

Note, dietary sources like oysters (~76 mg/3 oz), beef (~7 mg/3 oz), poultry (~2–3 mg/3 oz), beans, lentils, nuts, and whole grains provide zinc, but lozenges are key for therapeutic levels. 

Practical tip: At the first sign of a cold, consider ~15 mg elemental zinc lozenges every 2–3 hours (~75 mg/day) for up to 5 days (Nault et al., 2024).

Vitamin D: The Essential Immune Regulator

Vitamin D plays a pivotal role in immune regulation, notably by promoting the production of antimicrobial peptides such as cathelicidin, which help defend against respiratory pathogens (He et al., 2019). 

Athletes often exhibit suboptimal Vitamin D levels, primarily due to limited sun exposure from indoor training routines, potentially increasing their susceptibility to illnesses (Owens et al., 2018). A 2017 meta-analysis indicated that Vitamin D supplementation could offer modest protection against acute respiratory infections, particularly in individuals with baseline deficiencies (Martineau et al., 2017). However, a more recent 2025 meta-analysis encompassing 46 trials with over 64,000 participants found no statistically significant overall benefit of Vitamin D supplementation in preventing such infections (odds ratio 0.94), suggesting that its efficacy may be more pronounced in correcting deficiencies rather than in universal application (Jolliffe et al, 2025).

Mechanistically, maintaining optimal serum 25-hydroxyvitamin D levels (30-50 ng/mL) ensures effective antimicrobial peptide production and cytokine regulation, whereas deficiency (<20 ng/mL) can impair these immune defences, increasing infection risk - especially in athletes undergoing intense physical activity (He et al., 2019; Owens et al., 2018).

Practical Tip: To support immune function, consider supplementing with 1,000–2,000 IU of Vitamin D daily during periods of low sun exposure, ideally with blood monitoring to maintain appropriate serum levels (30–50 ng/mL) without exceeding safe limits (up to 4,000 IU/day per Endocrine Society guidelines).

Probiotics: Supporting Immunity from the Gut

Approximately 70% of the immune system resides in the gut, making it a critical hub for combating infections like colds and flu. Probiotic supplementation enhances immune function by reinforcing gut barrier integrity and mucosal immunity, aiding defence against respiratory infections (Jäger et al., 2019).

Regular intake may reduce the frequency, severity, and duration of colds and flu, especially during intense training, stress, or seasonal shifts, with emerging evidence suggesting benefits for viral clearance in conditions like COVID-19 (Hao et al., 2015; Olaimat et al., 2024). 

Effectiveness varies by strain and dose, with Lactobacillus and Bifidobacterium strains - such as Lactobacillus rhamnosus, Lactobacillus plantarum, and Bifidobacterium lactis - among the most studied (Jäger et al., 2019; Hao et al., 2015). 

New research also highlights next-gen probiotics like Faecalibacterium duncaniae for influenza protection (Chollet et al., 2024). 

Practical Tip: Start with 5-20 billion CFU daily of well-researched strains at least 2 weeks before peak exposure to stress, continuing consistently. Pair with probiotic-rich foods like yogurt, kefir, kimchi, or sauerkraut for ongoing gut and immune support.

Practical Takeaways:

Preventative Strategies:

• Vitamin D: 1,000-2,000 IU daily to maintain immune resilience, especially in low sun seasons.
• Probiotics: 5-20 billion CFU daily (e.g., Lactobacillus rhamnosus, Bifidobacterium lactis) via supplements (start 2 weeks before stress or exposure), or daily probiotic foods (yogurt, kefir etc).

At First Sign of Symptoms:

• Vitamin C: 500-1,000 mg/day, taken at symptom onset, to potentially shorten cold duration.
• Zinc Lozenges: ~75 mg/day total (split into 15 mg doses every 2-3 hours within 24 hours of symptoms) to potentially shorten cold severity.

Overall, remember that nutritional strategies play a supportive role rather than acting as a silver bullet when it comes to illness. And when you’re sick, always prioritise your doctor’s advice first. 

However, nutrition should be seen as an important piece of the puzzle for proactively maintaining a robust immune system and reactively supporting your recovery. 

That said, fundamentals like sleep, stress management, rest, and good hygiene will have the biggest impact. Think of nutrition as means to complement these foundations, helping to keep you resilient and, when needed, get you back to training faster.

References

Carr, A. C., & Maggini, S. (2017). Vitamin C and immune function. Nutrients, 9(11), 1211.

Chollet, L., et al. (2024). Faecalibacterium duncaniae as a novel next-generation probiotic against influenza. Frontiers in Immunology.

Gleeson, M. (2016). Immunological aspects of sport nutrition. Immunology and Cell Biology, 94(2), 117-123.

Hao, Q., Dong, B., & Wu, T. (2015). Probiotics for preventing acute upper respiratory tract infections. Cochrane Database of Systematic Reviews.

He, C. S., Aw Yong, X. H., Walsh, N. P., & Gleeson, M. (2019). Is there an optimal vitamin D status for immunity in athletes and military personnel? Exercise Immunology Review, 25, 42-64.

Hemilä, H. (2011). Zinc lozenges may shorten the duration of colds. Open Respiratory Medicine Journal, 5, 51-58.

Hemilä, H., & Chalker, E. (2013). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews.

Hemilä, H., Fitzgerald, J. T., Petrus, E. J., & Prasad, A. (2017). Zinc acetate lozenges may improve the recovery rate of common cold patients: An individual patient data meta-analysis. Open Forum Infect Dis.

Jäger, R., Mohr, A. E., Carpenter, K. C., Kerksick, C. M., Purpura, M., & Moussa, A. (2019). International society of sports nutrition position stand: probiotics. Journal of the International Society of Sports Nutrition, 16(1), 62.

Jolliffe, D. A., et al. (2025). Vitamin D supplementation to prevent acute respiratory infections: A systematic review and meta-analysis of 46 trials. The Lancet Endocrinology.

King, S., Glanville, J., Sanders, M. E., Fitzgerald, A., & Varley, D. (2014). Effectiveness of probiotics on the duration of illness in healthy children and adults who develop common acute respiratory infectious conditions. British Journal of Nutrition, 112(1), 41-54.

Martineau, A. R., Jolliffe, D. A., Hooper, R. L., Greenberg, L., Aloia, J. F., Bergman, P., Dubnov-Raz, G., Esposito, S., Ganmaa, D., Ginde, A. A., Goodall, E. C., Grant, C. C., Griffiths, C. J., Janssens, W., Laaksi, I., Manaseki-Holland, S., Mauger, D., Murdoch, D. R., Neale, R., Rees, J. R., Simpson, S. Jr., Stelmach, I., Kumar, G. T., Urashima, M., & Camargo, C. A. Jr. (2017). Vitamin D supplementation to prevent acute respiratory tract infections: Systematic review and meta-analysis of individual participant data. BMJ.

Mountjoy, M., et al. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. British Journal of Sports Medicine, 52(11), 687-697.

Olaimat, A. N., et al. (2024). Probiotics in the management of COVID-19: A systematic review. Nutrients, 16(3), 412.

Owens, D. J., Allison, R., & Close, G. L. (2018). Vitamin D and the athlete: Current perspectives and new challenges. Sports Medicine, 48(Suppl 1), 3-16.

Singh, M., & Das, R. R. (2013). Zinc for the common cold. Cochrane Database of Systematic Reviews.