Athlete Immunity: Nutrition Strategies to Keep you Competing

In light of recent events immunity has been a hot topic across the nation. It's inevitable, at some point in an athlete's career they will get sick, and this could limit their ability to train or even compete. While nutrition can't prevent illness from happening it can decrease the severity and duration of that illness.

Diet and lifestyle choices have a direct impact on immune function. The immune system is a complex matrix that regulates and executes defense throughout the body. For a better understanding of this relationship I'm going to provide a brief overview of this system.

General Overview of the Immune System:

The immune system acts to protect the host from a variety of threats, e.g. bacteria, viruses, fungi, and parasites. A well-functioning immune system provides defense against these harmful microbes by way of "resistance" and "tolerance". "Resistance" is how the body formulates an attack against threats and destroys microbes. If the attack is too strong, this can cause tissue damage and can be very costly in terms of energy expenditure. If the response is not strong enough, "suppressed", the threat will continue to place stress on the host. "Tolerance" is the body's ability to manage less threatening microbes at a non-damaging level. The table below outlines this concept.

Walsh, N.P. Nutrition and Athlete Immune Health: New Perspectives on an Old Paradigm.

Sports Med49, 153–168 (2019). https://doi.org/10.1007/s40279-019-01160-3

One school of thought is that athletes are at a greater risk for illness due to heavy training loads or over training. While this may be part of the problem, there are multiple factors that can play a role in an increased susceptibility for illness.

Athletes are predisposed to stressors that have been shown to suppress immunity; physical stress, psychological stress, sleep disruption, and low energy availability to name a few. Typically, all athletes experience some level of stress. Stress combined with one or more of these factors can increase risk for illness.

For the purpose of this article we'll focus on how diet can affect immunity, and how different nutrients can have a "tolerogenic" effect.

Macro Nutrient Considerations:

Macro nutrients include carbohydrates, proteins, and fats. The immune system requires adequate fuel from glucose, amino acids, and fatty acids for energy production. In addition, there needs to be an ample supply of nucleotides for DNA & RNA synthesis, amino acids for protein synthesis, and polyunsaturated fatty acids for eicosanoid (signaling molecules) synthesis.

Micro Nutrient Considerations:

Likely, a combination of both micro and macro nutrient deficiencies are responsible for a suppressed immune system. Micro nutrients include all of our vitamins and minerals. A handful of which are essential for proper immune function.

Iron, Zinc, Magnesium, Folic Acid

These micro nutrients play key roles in nucleotide and nucleic acid synthesis needed for DNA & RNA synthesis. Good sources of heme iron (more readily available iron) include; meat, fish, & poultry. Good sources of non-heme iron (less readily available iron) include; nuts, dark green vegetables, grains, dairy, & fortified foods. Zinc can be found in animal products, especially seafood and red meat.

Meta-analysis support the benefit of elemental zinc lozenges at the onset of a cold (< 24 hrs after). Athletes should consume 75 mg/day. Note: this amount would be hard to achieve through food alone

Magnesium is found in a wide variety of food; nuts, legumes, whole-grain cereals, beans, nut butters, seafood, & dark leafy greens. Folic acid can be found in green vegetables or fortified food/supplements (bio-availability is better in the supplement form). Typically, a well balanced diet will provide sufficient amounts of these nutrients. However, iron may be more of concern for female athletes (especially endurance runners).

Vitamin A & Vitamin D

Some vitamins and their metabolites regulate immune cell function. Vitamin A plays a key role in cell differentiation and gene expression. Vitamin D acts like a hormone and binds to receptors which can enhance or inhibit gene transcription. Good sources of Vitamin A include; milk, cheese, butter, eggs, tuna, & cod liver oil.

There are two forms of Vitamin D, D2 (less biological activity) & D3 (preferred form). Food sources include; eggs, salmon, tuna, fatty fish oil, & fortified products (milk, yogurt, OJ, breads, cereals). We can also produce D3 from 7-dehydrocholesterol, which is synthesized in the skin. Usually 5 - 15 minutes of sun exposure daily is sufficient, but this will also depend on skin color, season, geographical latitude, time of day, etc.

Vitamin D plays an important role in enhancing innate immunity. 1,000 - 2,000 IU/day is sufficient for athletes who meet the recommended 25(OH)D levels (> 40 ng/mL). Athletes who are insufficient or deficient should consider high-dose supplementation (5,000-10,000 IU/day) until levels are sufficient. Toxicity is possible but unlikely. 

Vitamin E & Vitamin C

Both Vitamin E & C function as antioxidants. Vitamin C is important for the regeneration of Vitamin E and the neutralization of free radicals. Both work to limit tissue damage and mitigate oxidative stress. Vitamin E can be found in plant oils; e.g. olive oil & avocado oil. Vitamin C should be consumed in the form of fresh fruits & vegetables, the fresher the better!

There is strong support for vitamin C supplementation to improve tolerance by inhibiting excessive tissue damage during infection. During periods of increased risk for infection a minimum of 0.25–1.0 g/day is recommended, with an upper limit of 2 g/day.

Pre & Probiotics

Prebiotics are typically non-digestible carbohydrates that feed the good bacteria in the gut. Common prebiotic foods include garlic, onions, whole grains and legumes. Probiotics are live microorganisms that can increase good gut bacteria. These microorganisms support the intestinal barrier, compete with pathogens in the gut, prime the immune system, and help prevent unnecessary inflammation. Good sources of probiotics include fermented foods such as; kombucha, kefir, & kimchi. Other foods with "live cultures" are also good options, such as greek yogurt or cottage cheese. If you are not a fan of these foods, supplementation may be a good option.

The research involving athletes is small and still emerging but studies to date indicate some benefit.

Supplement Consideration:

With supplements the assumption is "more is better", but this isn't always the case. There is always some level of risk associated with supplementing. Blunted training adaptations due to regular high-dose exposure is of concern. There is also risk for toxicity in certain cases. While continuous high-dose exposure is not ideal, supplementing during times of increased susceptibility, e.g. leading up to competition & travel, may be beneficial. Supplementation should be done in a manner that reduces the infectious burden and decrease duration with the athletes well-being in mind.

Key Takeaways:

1. Under fueling can lead to compromised immune function. Especially when protein intake is insufficient. To avoid this, ensure you are fueling adequately for the amount of work you are doing. If you are in an intentional energy deficit, increase protein to preserve lean muscle mass and immune function.

2. Avoid micro nutrient insufficiency/deficiency. Consume a balanced diet with a variety of foods. In certain instances food may not be enough, especially for elite athletes. If possible, have labs done to assess your current status.

3. Consume 75mg of zinc at the onset of a cold.

4. Supplementation of Vitamin C, Vitamin D, & probiotics may be indicated leading up to/during travel or competition.

*Remember to always consult with a Registered Dietitian (RD) for individualized recommendations.

References:

Walsh, N.P. (2019) Nutrition and Athlete Immune Health: New Perspectives on an Old Paradigm.                    
Sports Med49, 153–168. https://doi.org/10.1007/s40279-019-01160-3

Colbey, C., Cox, A.J., Pyne, D.B. et al. (2018) Upper Respiratory Symptoms, Gut Health and Mucosal Immunity in Athletes.                     
Sports Med48, 65–77. https://doi.org/10.1007/s40279-017-0846-4

Walsh, N.P. (2018) Recommendations to Maintain Immune Health in Athletes.
European Journal of Sport Science, 18:6, 820-831. DOI: 10.1080/17461391.2018.1449895

Hao Q, Dong BR, Wu T. (2015) Probiotics for preventing acute upper respiratory tract infections. 
Cochrane Database of Systematic Reviews, Issue 2. Art. No.: CD006895. DOI:10.1002/14651858.CD006895.pub3.

Hemilä  H, Chalker  E. (2013) Vitamin C for preventing and treating the common cold. 
Cochrane Database of Systematic Reviews, Issue 1. Art. No.: CD000980. DOI: 10.1002/14651858.CD000980.pub4.

Calder, P. (2012) Feeding the immune system. 
Proceedings of the Nutrition Society, 72, 299–309. DOI:10.1017/S0029665113001286