By Performance Nutritionist, Tamara Walker book a 1-2-1 with Tam here

Winter brings colder temperatures, more time spent indoors and an increase in circulating viruses. This makes young athletes more vulnerable to the seasonal flu. Even a short-term illness, can reduce strength, stamina, motivation and performance. Understanding how the immune system works, how nutrition supports it and when it is safe to resume training helps athletes stay healthy and return stronger. 

1. Why Winter Increases Illness Risk

Flu viruses survive for longer in cold, dry air, and they spread more easily when people are indoors together during training, matches and travel situations such as minibuses or changing rooms (1). In these close-contact areas, germs can spread through the air and on surfaces, making it easier for people to catch them.

Reduced winter sunlight may also lower vitamin D levels. Vitamin D contributes to immune regulation, so insufficient levels can increase susceptibility to respiratory infections (2). Cold air can further dry out the airways and weaken natural barriers that normally help prevent viruses entering the body.

2. What Happens to Your Body When You Are Sick

Innate Immune System: Rapid Defence

The innate immune system reacts immediately when the flu virus enters the body. This includes:

·      Fever, which raises body temperature to slow viral replication (3)

·      Inflammation, producing tiredness and muscle soreness

·      Increased mucus production, helping trap viral particles

·      Activation of white blood cells, which attack infected cells

These symptoms often appear quickly and show that the body is actively working to control the infection.

Adaptive Immune System: Targeted Defence

The adaptive system builds a more specific response:

·      B cells produce antibodies targeting the influenza virus (4)

·      T cells destroy infected cells, reducing viral load

·      Memory cells form, helping with faster responses in future infections

A significant amount of energy is diverted to these processes, making athletes commonly experience decreased strength, reduced endurance and slower decision making during illness (3).

3. Nutrition for Strong Immunity

A. Adequate Energy Intake

Young athletes often under-eat during busy school and training schedules. Low energy availability increases stress hormones and suppresses immune function (2). Eating regularly and meeting energy needs is key during training blocks and illness.

B. Key Immune Nutrients

Nutrients that support immune cell function include:

·      Vitamin C (berries, peppers, citrus)

·      Vitamin D (oily fish, fortified foods, sunlight exposure) (2)

·      Zinc (meat, seeds, nuts)

·      Protein (supports immune cell growth and repair)

·      Omega-3 fats (salmon, walnuts, chia seeds), which help regulate inflammation

C. Hydration Is Essential

Fever and increased breathing rate cause the body to lose more fluids. Even mild dehydration can slow recovery and increase fatigue [1]. Drinking warm liquids, such as soups or herbal teas, can help keep you hydrated and soothe a sore throat. A small drop in hydration can also affect concentration and decision making, which are important for safe training and performance.

D. Support Gut Health

A well-nourished gut microbiome plays a key role in immune regulation and inflammation control. A healthy gut supports a more stable immune response and may help athletes respond better during winter months (2). Helpful foods include:

·      Yoghurt / kefir

·      Fermented vegetables (sauerkraut, kombucha)

·      High-fibre wholegrains and fruit

4. Sleep: The Ultimate Immune Booster

Sleep enhances immune function by supporting antibody production and regulating immune signalling. Poor sleep is linked to increased risk of respiratory infections and slower recovery (5). Young athletes should aim for 8 to 10 hours of sleep per night, with additional rest when unwell. Adequate sleep also improves focus, reaction time and movement coordination, all of which can decline during illness.

5. Return to Play: When Is It Safe?

Returning too early can prolong illness, increase injury risk and worsen overall fatigue. Sports medicine guidelines offer clear recommendations (6).

The Neck Rule

·      Above-the-neck symptoms (runny nose, mild headache or sore throat):

 Light activity may be acceptable.

·      Below-the-neck symptoms (fever, chest congestion, deep cough, body aches):

 Training should be avoided.

Fever Requires Complete Rest

Athletes should be fever free for at least 24 hours without medication before resuming exercise (6).

Gradual Return to Play Progression

1.        Light activity: Walking or gentle cycling

2.        Low intensity training: Relaxed aerobic exercise

3.        Moderate sport skills: Technical drills, non-contact

4.        Full training: Normal sessions

5.        Competition: Only once entirely symptom free

If symptoms worsen at any stage, athletes should step back to the previous level.

6. Protecting Team Mates

Prevention helps protect both individual athletes and the wider team (1). Recommended habits include:

·      Regular handwashing

·      Avoiding shared bottles and towels

·      Covering coughs and sneezes

·      Staying home when ill

·      Cleaning shared equipment

Summary

Winter flu season can make young athletes more likely to get sick because of colder weather, less sunlight and more time spent indoors. When athletes become ill, the body focuses on fighting infection, which can reduce energy, strength and performance. Eating well, staying hydrated, supporting gut health, and getting enough sleep all help the immune system work effectively. Returning to training should be gradual and only after symptoms improve, with fever-free rest being essential. Practising good hygiene protects both the athlete and their team from spreading germs.

By Performance Nutritionist, Tamara Walker book a 1-2-1 with Tam here

Disclaimer: This article is intended to provide general information about nutrition for youth athletes and is not meant to replace professional dietary advice or individual nutritional counselling. Every child's nutritional needs can vary due to factors such as age, size, physical activity level, and medical conditions. We strongly recommend consulting with a registered dietitian or a healthcare provider before making changes to your child's diet, such as adding food powders. YSN and the author of this article do not take responsibility for any possible consequences from any treatment, procedure, dietary modification, action, or application of medication which results from reading or following the information contained in this article.

References

1.        Centers for Disease Control and Prevention. How flu spreads. Atlanta: CDC; 2024.

2.        Calder PC. Nutrition and immunity: lessons for athletes. Sports Med. 2020;50(1):1–10.

3.        Gleeson M. Immune function in sport and exercise. J Appl Physiol. 2007;103(2):693–9.

4.        Walsh NP, Gleeson M, Pyne DB, Nieman DC, Dhabhar FS, Shephard RJ, et al. Position statement: Part one. Immune function and exercise. Exerc Immunol Rev. 2011;17:6–63.

5.        Irwin MR. Sleep and inflammation: partners in sickness and in health. Nat Rev Immunol. 2019;19(11):702–15.

6.        American College of Sports Medicine. Illness and exercise: return to play guidance. Indianapolis: ACSM; 2023.