We’ve all been there: You’ve trained hard for an event and then suddenly you get sick. In many cases this is simply because your body’s immunity is low as a result of intensive exercise. Compared to moderate physical activity, prolonged exercise (lasting longer than 90 minutes) and intensive exertion cause numerous changes in our immune function. Each bout of exercise causes physiological stress and a depression of the immune function, and post-exercise immune depression seems to be most pronounced when:
• we exercise for longer than 90 minutes,
• the exercise is of moderate-to-high intensity,
• the exercise is done without carbohydrate ingestion.
WHEN TO BE CAREFUL
The risk of illness or infection is highest three to 72 hours after prolonged exercise, with upper respiratory tract infection being the most common. Factors affecting the resistance to illness during or following an event include:
• Cumulative stress of intense training (exercise intensity and duration as well as fitness level of the athlete),
• Nutritional status,
• Training nutrition,
• Recovery nutrition.
Athletes who are at risk include those who have inadequate dietary intake, such as women who restrict their energy intake or vegetarians, as well as athletes who have excessive intakes, i.e. athletes who consume a large amount of supplements at the expense of micronutrient density or have unbalanced diets such as high carbohydrate diets at the expense of protein.
THE RIGHT DIET
Although uncommon, inadequate protein intake can impair immune function, leading to an increased incidence of infections. However, extreme deficiencies are unlikely to be seen in athletes, even in vegetarians with low protein intakes. Athletes who are overtrained or fatigued may benefit from slightly higher protein intakes.
Dietary carbohydrates are critical fuel for both muscle and immune cells. When you exercise or when your blood sugar is low due to training, there might be an increase in the release of the stress hormones, cortisol and adrenalin, and a reduction of growth hormone. When athletes train in a carbohydrate-depleted state, it affects their immune cells. It is therefore important to match your carbohydrate intake according to your training load.
There is evidence to suggest that carbohydrate intake during a marathon may decrease the incidence of post-marathon upper respiratory tract infections, although more research is needed. It is recommended that 30-60g of carbs be ingested per hour during prolonged exercise.
Vitamins A, C, E, B6, B12 and an adequate amount of the minerals iron, zinc, magnesium, copper, selenium and manganese are important in maintaining the immune system. Most Western diets meet these requirements, but eating foods rich in these minerals and vitamins are encouraged. Just remember, a mega-dosing on supplements such as Vitamin E and Zinc may have harmful effects on the immune system!
• Avoid deficiencies and ensure adequate intake of carbs, protein, fluids and micronutrients (Iron, Zinc and Vitamins B6, B12,C and E).
• Ensure adequate carbohydrate intake (30-60 grams per hour) during prolonged or high-intensity exercise sessions.
• Take a broad range multivitamin/mineral supplement to support restricted intake. (This is especially important when athletes are travelling or when dietary variety is limited.)
• Vitamin C and probiotic supplementation during intense training and prior to ultra-endurance events is important.
• Iron supplements should not be taken during periods of infection.
• Avoid dehydration, as saliva contains immune cells which help fight opportunist infections entering the digestive tract.
• A regular consumption of probiotics can result in fewer days of respiratory illness and lower severity of the symptoms of upper respiratory track infections.
PRACTICAL TIPS TO REDUCE THE RISK OF ILLNESS
• Avoid getting a dry mouth, both during competition and rest.
• Avoid sharing drink bottles, cutlery or towels.
• Travelling athletes should only drink bottled water.
• Ensure good hygiene practices at all times, e.g. washing hands.
• Avoid putting your hands to your eyes.
• Get adequate sleep.
• Reduce social/life stresses.
• Avoid rapid weight-loss.
• Ensure adequate recovery between exercise sessions.
TOP FOODS TO HELP BOOST IMMUNITY
Plain low-fat cultures yoghurt is a good source of probiotics, as well as carbohydrates and protein.
Oat bran contains Beta-glucan, which has been shown to stimulate immune defences and increase resistance to a wide variety of infections.
Turmeric – the yellow pigment found in turmeric is called cucumin, which has been shown to modulate the activation of immune cells and regulate the expression of inflammatory cells.
Oily fish is an excellent source of high-biological value protein, iron and omega 3, all of which help regulate the immune system. Omega 3 also has an anti-inflammatory affect.
Garlic contains antibacterial, antifungal, antiviral properties that help fight infection, as well as properties which help boost immune cells.
Guava can provide as much as 228mg of vitamin C per 100g serving, 377mg per cup, and 126mg per fruit.