Immune health, nutrition and performance.
Optimising immune health has a central role in athlete’s performance, given the potential for missed training and competitions related to illness. It’s widely accepted that moderate training enhances immune function. However, there has historically been considered to be a ‘tipping point’ whereby high training loads suppress immune defenses, increasing the risk of infection (especially upper respiratory tract infections (URTIs)) (Walsh et al., 2011).
More recent research is reshaping how we think about the effects of heavy training on immune function — moving away from believing it directly suppresses immunity, and recognizing a more complex, multi-factorial interplay. Infection risk around training and competition often relate more to secondary stressors: travel, poor sleep, inadequate nutrition and psychological factors (stress, anxiety, depression) rather than to exercise itself (Walsh, 2019).
Therefore, exercise itself does not necessarily weaken immunity. Instead, immune health depends on how training and competition interplay with lifestyle, environment, and recovery. Nutrition is a key modifiable factor for athletes’ immune health. Proper sports nutrition should not only support training adaptation and athletic performance but also optimise immune function.
Core principles in nutrition and immune health
Fuel adequately: Under-fuelled training can increase stress on the immune system, exacerbating transient post-exercise immune dysregulation. Chronic low energy availability weakens innate and adaptive immune responses (alongside numerous other health parameters) (Gleeson, 2016). Insufficient total energy intake also increases the potential for macro- and micro-nutrient deficiencies.
Carbohydrate timing and quantity: Fuelling long or intense sessions with sufficient carbohydrates maintains blood glucose levels, reduces stress hormones and regulates immune function. Low-carb training may sometimes be useful for adaptation, but should be strategically implemented to mitigate impacts on immunity (Walsh, 2019).
Protein + micronutrients: Protein supports recovery and is essential for immune cell synthesis and repair. Key micronutrients to consider for most athletes include iron, vitamin C (for iron absorption and secondary functions) and vitamin D, as these carry the highest risk of deficiencies. Zinc, Vitamins A, E, B6, and B12 are essential but can typically be met through a balanced diet without significant risk of deficits (other than for those following plant-based diets or with certain clinical conditions) (Phillips & Van Loon, 2011; He et al., 2016).
Supplements are often not needed (and may be harmful): A food first approach should always be the foundation – supplementation is often not required in the presence of a balanced diet. Importantly, taking supplements in the absence of diagnosed deficiencies carries notable health risks. If in doubt, discuss concerns with a dietitian or doctor (Nieman, 2019).
Gut health counts: Some probiotics have been shown to reduce illness risk in athletes, especially during travel or high training loads. However, effects are modest and further research on dose and strains is required. Promoting a healthy gut microbiota through diet is likely to have immune benefits: aim for diversity, varied vegetables and fruits, and fermented options (Kimchi, plain yoghurt, Kefur etc) (West et al., 2015).
Lifestyle is key: Sleep, stress, and recovery are as important as what’s on your plate (Walsh, 2019).
What Periodized Nutrition Adds
Just as training is structured into cycles, nutrition should also adapt:
Macro: Align energy and nutrient goals with the base, build, and peak phases.
Meso: Adjust food intake to match heavier or lighter training blocks.
Micro: Plan around the specific session—fuel hard days well, allow lighter fuelling on recovery days if appropriate (Stellingwerff et al., 2025):
This adaptive approach prevents chronic under-fuelling, whilst ensuring that nutrition supports both performance and immunity at crucial points in the training and competition cycle.
How periodized nutrition can benefit immune health:
Heavy load/competition weeks: Prioritise carbs before and during training, ensure total energy intake is high enough, and don’t skimp on sleep. These are peak illness risk times (Walsh, 2019).
Off-season/lower stress blocks: Safe moments to experiment with metabolic strategies (like “train-low” sessions), as the immune system is under less strain (Stellingwerff et al., 2025).
Stay adaptable: Monitor how you’re feeling and responding to training. If illness symptoms or fatigue spike, switch back to conservative fuelling and focus on recovery (Gleeson, 2016).
Practical recommendations
Monitor training, illness, and recovery markers.
Fuel adequately, especially around key sessions.
Supplement Vitamin D from October to April in the UK (Athletes may have increased requirements: 1,000-4,000IU daily)
Be mindful of iron deficiency risk (high-volume runners, women who menstruate, vegans/vegetarians) and symptoms. Include dietary sources and seek clinical input if deficiency suspected.
Prioritise structured recovery, tapering, and practice sleep hygiene.
Consider use of probiotics strategically during high‐risk periods.
Include omega‐3s, fruits, and vegetables as part of a varied, balanced diet.
Adapt strategies dynamically in response to lifestyle risk factors and symptoms of illness.
In summary
High training loads, particularly in the presence of other lifestyle risk factors, may increase athletes vulnerability to illness. Nutrition isn’t fixed – it should be adapted around training and lifestyle demands to maximise strength, endurance and immune health. Food-based dietary adjustments are sufficient for most, without the need for additional supplementation (with the exception of Vitamin D). By integrating smart fuelling in a periodized approach, athletes can optimise immune resistance and tolerance, sustain performance and reduce illness risk at critical points.
References
Campbell, J.P., & Turner, J.E. (2018). Debunking the myth of exercise-induced immune suppression: Redefining the impact of exercise on immunological health across the lifespan. Frontiers in Immunology, 9, 648.
Gleeson, M. (2016). Immunological aspects of sport nutrition. Immunology and Cell Biology, 94(2), 117–123.
He, C.S., et al. (2016). Vitamin D status and its influence on mucosal immunity in athletes. Exercise Immunology Review, 22, 38–62.
Nieman, D.C. (2019). Exercise, infection, and immunity. International Journal of Sport Nutrition and Exercise Metabolism, 29(2), 117–127.
Phillips, S.M., & Van Loon, L.J. (2011). Dietary protein for athletes: From requirements to metabolic advantage. Applied Physiology, Nutrition and metabolism, 36(5), 647–654.
Stellingwerff, T., et al. (2025). A framework for periodized nutrition for athletics. Journal of Sports Nutrition.
Walsh, N.P., et al. (2011). Position statement. Part one: Immune function and exercise. Exercise Immunology Review, 17, 6–63.
Walsh, N.P. (2019). Nutrition and athlete immune health: New perspectives on an old paradigm. Sports Medicine, 49(2), 153–168.
West, N.P., et al. (2015). Probiotics, immunity and exercise: A review. Exercise Immunology Review, 21, 107–146.