Immune function, nutrition and the athlete- Practical recommendations

It’s vital for athletes to take on the correct fuel before and after sport to perform at their peak. Here is our guide.

Ted Munson

It’s vital for athletes to take on the correct fuel before and after sport to perform at their peak. Here is our guide.


Strong evidence indicates that physical activity influences immune function and risk of certain types of infection, such as upper respiratory tract infections (URTI). Many components of the immune system exhibit change after prolonged heavy exertion. During this ‘open window’ of altered immunity (which may last between 3 and 72 hours, depending on the parameter measured), viruses and bacteria may gain a foothold, increasing the risk of subclinical and clinical infection. Prolonged bouts of strenuous exercise have been shown to result in transient depression of white blood cell (leukocyte) functions which may be the cause of impaired immune function, increasing the risk of infection1. This review aims to explore the nutrition applications that aim to combat impaired immune function in athletes.

First and foremost, ensure a varied diet is consumed and do not neglect any macronutrients, especially carbohydrate that is an essential fuel for the cells of the immune system. High-carbohydrate diets are designed to keep the liver and muscle stores of glycogen high to ensure glucose/glycogen availability during exercise and may even help attenuate increases in stress hormone2. Aim to keep carbohydrate at 50% of energy intake and protein at least over 1.2g/kg. A common mistake/ method used by athletes is to reduce carbohydrate intake throughout winter to assist body composition while out of competition. While ”fuelling for the work required” is recommended3, fuelling with carbohydrate helps avoid chronic low energy availability. As a general rule of thumb, when exercising over 90 minutes, consume around 60g of carbohydrate per hour. This helps lower circulating stress hormone and anti-inflammatory cytokine responses, while delaying the symptoms of overreaching during intensive training periods4. Treat this particular session as your “train as you race session” and only practice low energy/ fasting during low- moderate exercise and ensure sufficient refuelling.


When training sessions are performed with low carbohydrate availability, it is not recommended that this is done for more than a few days per week4. If the aim is “weight loss”, athletes are more likely to be infection prone, as such a multivitamin supplement may be beneficial to support restricted food intake4. Athletes reducing carbohydrate intake for training adaptations are risking reduced immune function and a balance must be struck weighing up body composition and keeping well. After fasted sessions with low energy availability, refuelling is key to bolster immunity. Current refuelling guidelines suggest the consumption of 1.0–1.2 g/kg/h within the first hour of exercise cessation and the continuation of a carbohydrate intake of 1.0–1.2 g/kg/h for 4–6 h, or until regular meals resume5.

Athletes should always “eat the rainbow” and take 5+ fruit and vegetable portions per day. Varying colours of fruit and vegetables should be consumed, with varying vitamins and minerals in each different food. For example, spinach is an excellent source of vitamin K and A, while strawberries and kiwis are rich in vitamin C. Polyphenols are a large class of chemical compounds synthesized by fruits, vegetables and other plants that possess health benefits. Flavonoids are the best-defined group of polyphenols in the diet, providing flavour and colour to fruits and vegetables. There are six major subclasses of flavonoids, including flavonols, the subclass that includes quercetin – with research suggesting quercetin supplementation can have anti-inflammatory and pro immune effects, especially when coingested with other flavonoids and micronutrients6. Other evidence suggests that quercetin and green tea can reduce upper respiratory symptoms in highly physical active individuals4. Other flavonoids have also shown positive effects on immune function7 8. Always eat a varied diet and possibly supplement if undergoing periods of food restriction e.g travelling.

Vitamin D has a key role to play when maintaining a healthy immune system9, with many athletes deficient in the winter months5. During winter months, it is recommended to take a vitamin D supplement to avoid deficiency (25(OH) D G50 nmol/L)5. How much? A study on professional swimmers found that a daily vitamin d supplement containing 4000iu of vitamin d was enough to maintain levels for 6 months compared to a placebo10. Other supplements like probiotics may even reduce the risk of gastrointestinal infections by improving gut barrier function11 and may even reduce the duration and incidence of infections in elite Rugby players12. It has also been suggested to take a zinc supplement (e.g lozenge) at the onset of a cold or in the build-up to an important competition, in case a URTI begins at such an important time4.

Considering lifestyle based factors, increasing amounts of evidence suggest that sleep deprivation can have detrimental effects on immune function, and that immune responses feed-back on sleep architecture13. A review examining the link between sleep and immunity concluded that sleep improves immune responses and that most immune cells have their peak pro-inflammatory activity at night13. Disruptions in endocrine and physiological circadian rhythms due to sleep deprivation may result in impaired immune responses14. In addition, while moderate exercise may benefit immune function and provide a range of health benefits, heavy exertion by endurance athletes leads to transient immunosuppression and increased risk of infection15. However, it is unclear what defines “heavy exercise” and may be individual depending on the athletes training status.


More research needs to be done in applied athlete settings to determine conclusions of the effect of nutrition supplements on immune function. However, there is evidence to suggest the use of vitamin D, polyphenols (flavonoids), zinc and probiotics to help promote immune function. An athlete should place emphasis on consuming more fruit and vegetables along with a varied diet. While train low strategies may be practiced, it is important to “fuel for the work required” and fuel longer/ intense sessions for enhanced immune function.



  1. Walsh, N.P., M. Gleeson, R.J. Shephard, M. Gleeson, J.A. Woods, N.C.Bishop, M. Fleshner, C. Green, B.K. Pedersen, L. Hoffman-Goetz, C.J. Rogers, H. Northoff, A. Abbasi, and P. Simon (2011). Position Statement Part One: Immune function and exercise. Exercise Immunology Review, 17, 6-63.
  2. Venkatraman, J. T., & Pendergast, D. R. (2002). Effect of dietary intake on immune function in athletes. Sports Medicine32(5), 323-337.
  3. Impey, S. G., Hammond, K. M., Shepherd, S. O., Sharples, A. P., Stewart, C., Limb, M., & Close, G. L. (2016). Fuel for the work required: a practical approach to amalgamating train‐low paradigms for endurance athletes. Physiological Reports4(10), e12803.
  4. Gleeson, M. (2015). Effects of exercise on immune function. Sports Science Exchange28(151), 1-6.
  5. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. Medicine and Science in Sports and Exercise48(3), 543-568.
  6. Nieman, D. C., Henson, D. A., Maxwell, K. R., Williams, A. S., Mcanulty, S. R., Jin, F., & Lines, T. C. (2009). Effects of quercetin and EGCG on mitochondrial biogenesis and immunity. Medicine & Science in Sports & Exercise41(7), 1467-1475.
  7. Somerville, V. S., Braakhuis, A. J., & Hopkins, W. G. (2016). Effect of flavonoids on upper respiratory tract infections and immune function: A systematic review and meta-analysis. Advances in Nutrition: An International Review Journal7(3), 488-497.
  8. Zhang, H., & Tsao, R. (2016). Dietary polyphenols, oxidative stress and antioxidant and anti-inflammatory effects. Current Opinion in Food Science8, 33-42.
  9. Chun, R. F., Liu, P. T., Modlin, R. L., Adams, J. S., & Hewison, M. (2014). Impact of vitamin D on immune function: lessons learned from genome-wide analysis. Frontiers in Physiology5, 151
  10. Lewis, R. M., Redzic, M., & Thomas, D. T. (2013). The effects of season-long vitamin D supplementation on collegiate swimmers and divers. International Journal of Sport Nutrition and Exercise Metabolism23(5), 431-440.
  11. Mengheri, E. (2008). Health, probiotics, and inflammation. Journal of Clinical Gastroenterology42, 177-178.
  12. Haywood, B. A., Black, K. E., Baker, D., McGarvey, J., Healey, P., & Brown, R. C. (2014). Probiotic supplementation reduces the duration and incidence of infections but not severity in elite rugby union players. Journal of Science and Medicine in Sport17(4), 356-360.
  13. Bollinger, T., Bollinger, A., Oster, H., & Solbach, W. (2010). Sleep, immunity, and circadian clocks: a mechanistic model. Gerontology56(6), 574-580.
  14. Halson, S. L. (2014). Sleep in elite athletes and nutritional interventions to enhance sleep. Sports Medicine44(1), 13-23.
  15. Nieman, D. C., & Pedersen, B. K. (1999). Exercise and immune function. Sports Medicine27(2), 73-80.

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