Strengthening The Immune System In Runners
Mako Running athlete Michael H. starting the recovery process immediately after training.
Distance runners are conditioned to tolerate stress. Mile after mile, we expose the body to controlled fatigue in pursuit of adaptation. But while the cardiovascular and muscular systems grow stronger through this process, the immune system can become temporarily vulnerable.
If you’ve ever trained hard for weeks only to be sidelined by a cold, sore throat, or lingering fatigue, you’ve felt this tension firsthand. Performance doesn’t exist in isolation from health. In fact, long-term performance is built on it. Understanding how endurance training affects immunity - and how to protect it - is essential for sustainable progress.
The Immune System and Endurance Training
Endurance training places a significant physiological load on the body. High-intensity sessions, long runs, and accumulated fatigue all stimulate adaptation — but they also create temporary stress on immune function.
Research describes this vulnerability as the “open window”: a short-term period following intense exercise where immune defences are suppressed. This window may last from a few hours up to 72 hours depending on session intensity, duration, and recovery quality (Walsh et al., 2011).
This temporary suppression is driven by oxidative stress, inflammation, hormonal shifts, and redistribution of immune cells. During this window, pathogens such as cold and flu viruses have a greater opportunity to gain a foothold (Gleeson et al., 2011).
Female athlete stretching and recovering after a run.
“Fitness improves through stress, but immunity survives through balance.”
Key Vitamins and Minerals for Immune Health
The immune system is nutrient dependent. Without sufficient building blocks, its ability to respond to stress, repair tissue, and fight infection becomes compromised. Runners in heavy training blocks must be especially attentive to the following micronutrients:
Vitamin C
A potent antioxidant that reduces oxidative stress and supports immune cell function. Found in citrus fruits, berries, peppers, and leafy greens (Carr & Maggini, 2017).
Vitamin D
Essential for immune regulation and inflammation control. Obtained primarily through sunlight exposure and foods such as fatty fish, eggs, and fortified dairy products (Calder et al., 2013). Deficiency is common in UK athletes during winter.
Zinc
Plays a direct role in immune cell development and antiviral defence. Rich sources include red meat, poultry, shellfish, legumes, and seeds (Gammoh & Rink, 2017).
Iron
Necessary for oxygen transport and immune cell proliferation. Runners can obtain iron from lean meats, fortified cereals, beans, and dark leafy vegetables (McClung & Murray-Kolb, 2015).
Omega-3 Fatty Acids
Anti-inflammatory compounds found in oily fish, flaxseeds, and walnuts. These help regulate immune signalling and tissue repair (Calder, 2013).
Immune supporting food include citrus fruits, salmon, leafy greens and nuts
Strategies to Enhance Immunity in Runners
Building a resilient immune system doesn’t require exotic solutions. It requires consistent execution of simple principles — done well.
1. Balanced Nutrition
A varied diet rich in fruits, vegetables, lean proteins, whole grains, and healthy fats forms the foundation of immune health. Athletes relying too heavily on ultra-processed convenience foods often undermine their recovery without realising it.
2. Timing of Meals
Consuming carbohydrates and protein within the post-exercise “open window” helps blunt immune suppression and accelerates tissue repair (Walsh et al., 2011).
3. Hydration
Even mild dehydration weakens immune responses. Runners should maintain consistent fluid intake before, during, and after training (Sawka et al., 2015).
4. Rest and Sleep
Sleep is one of the most powerful immune enhancers available. During deep sleep, immune cell production and tissue repair peak (Simpson et al., 2017). Chronic sleep restriction is one of the fastest routes to illness.
5. Supplement with Intelligence
When dietary intake is insufficient, targeted supplementation may help - particularly vitamin D during winter months. However, supplements should support, not replace, good nutrition and should always be taken with professional guidance (Gleeson, 2013).
“The immune system isn’t strengthened by extremes - it’s fortified by consistency.”
Coach’s Insight
Illness is rarely bad luck, it’s usually feedback. When runners fall ill repeatedly, it’s almost always a reflection of cumulative stress, under-fuelling, poor sleep, or inadequate recovery between sessions.
The strongest athletes I coach aren’t the ones training hardest, they’re the ones managing stress best. They protect sleep. They fuel deliberately. They respect recovery. And because of that, they train consistently while others cycle between fitness, fatigue and injury.
Final Takeaway
Your immune system is not separate from your performance, it is one of its foundations. Heavy training can temporarily weaken immune defences, but intelligent recovery, robust nutrition, hydration, and sleep can tip the balance back in your favour.
Protect your health with the same discipline you apply to your training, and you’ll build not just speed and endurance, but durability. Because the strongest runners aren’t just the fittest. They’re the ones who stay healthy.
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