Sports nutrition: strengthening your immune system

Why does immunity suffer in the winter?

The immune system

• The ‘innate’ immune system – the first line of defence, which is designed to stop invaders from entering the body in the first place. The innate system is made up of physical barriers (eg the skin and epithelial tissues of the lungs, nose and intestinal tract), chemical barriers (eg the high acidity of the stomach, and the fluid secreted by the tear ducts) and cellular barriers (eg phagocytic cells, whose job is to engulf invaders).
• The ‘acquired’ immune system – the second line of defence, employing a large number of different cell types, which not only communicate with each other, but also work in cooperation to help the body recognise and defeat the invaders that have managed to breach the first line of defence. Your acquired immunity is the reason you don’t (usually) have a second bout of the same virus once you’ve recovered from the initial illness. Even when an unfamiliar pathogen breaches your initial defences, a healthy acquired immune system can ensure that any subsequent illness is far shorter in duration and less severe than it would otherwise be.

• Air temperature and central heating – in winter the air is cold and this makes it dry. This tends to dry out the epithelial tissues, which form part of your innate immune system and are especially protective against URTIs. This in turns reduces their efficiency, making an infection more likely. The situation is made even worse by central heating, because cold dry air becomes even drier when warmed. Note too that, contrary to popular belief, exercising outdoors in wet and windy weather is less likely to precipitate an URTI, because wet or damp air is moist and so less drying for the throat and nose than crisp, cold air!
• Air quality – you’ve probably noticed that the weather outside in winter isn’t great! This means that in most homes and offices, the windows are firmly shut, which not only recycles the air, but also the bugs floating around in that air, increasing your risk of exposure to pathogens. If you work in a large office, the chances are that the air-conditioning system will do an excellent job of making sure you get exposed to your fair share of your colleagues’ winter bugs!
• Nutrition – is extremely important for immunity. Unfortunately, the quality of our nutrition often nosedives during the winter months – at the very time it really needs to be optimised! For example, an ample supply of vitamin A is essential for the innate immune system to operate at full capacity. However, in winter, nutrients like vitamin A (found in red, orange and dark green fruits and vegetables) tend to be in shorter supply in the diet because many people consume much smaller quantities of fruits and vegetables, preferring warm, stodgy and comforting foods instead. The same is true of the acquired immune system, which needs an amply supply of a wide range of nutrients to operate at full potential. Any shortfall in just one single nutrient can adversely affect immunity. This explains why your immunity can be used as an excellent barometer of your overall nutrition status. The post-Christmas surge in URTIs is no coincidence either; Christmas is invariably associated with increased alcohol intake (a known immune depressant), less than healthy ‘seasonal fare’ and the all too common stress and fatigue that accompany the season, all of which deplete immunity!

Key nutrients for immunity

• Day-to-day nutrition – ie, the kind of dietary principles you need to be following everyday regardless of your training routine;
• Exercise nutrition – ie, what you need to think about before, during and after training.

Day-to-day nutrition

• Vitamin A – well supplied in liver, eggs, all orange and red fruits and vegetables such as carrots, sweet potatoes, apricots.
• Vitamin C – found in citrus fruits such as oranges and grapefruits, kiwis, all the berries, also well supplied in tomatoes and peppers.
• Vitamin D – good sources include eggs, milk, butter, cod liver oil (see box on supplements) and some other fish oils.
• Essential fatty acids (ie omega-3 and omega-6 oils) – good sources include all the fatty fish (trout, sardines, herrings, salmon, mackerel, pilchards, etc) as well as unrefined whole grains and nuts and seeds, especially, hemp, flax, walnuts and pumpkin seeds.

• Zinc – a vital immune nutrient; good sources are high quality, lean cuts of meat and fish and shellfish; also found in whole grains and some nuts and seeds, such as walnuts and pumpkin seeds.
• Selenium – well supplied in unrefined whole grains (eg wholemeal bread), all seafood and some nuts and seeds, especially Brazil nuts.

Post-exercise nutritional strategy

• Dietary carbohydrate – Ensure your everyday diet provides an ample supply of carbohydrate at all times, with around 60% or more of calories from carbohydrates (unprocessed, whole grain breads, pasta and cereals, rice, corn, all types of fruits and vegetables, beans, peas and lentils). This is important, even on days when you don’t train, because it’s during these rest days that you really can top up depleted glycogen reserves. If you train in the evenings, make sure you consume sufficient carbohydrate both at breakfast and lunchtime;
• Carbohydrate drinks – For longer (60+ minutes) or more intense training sessions, you should consume 500-1000mls of a 6% carbohydrate drink (around 60 grams of carbohydrate per litre of water) each hour during training. This will help to reduce the extent of carbohydrate depletion during exercise. Recent research suggests that carbohydrate drinks containing small amounts of protein may be even more efficient at reducing muscle breakdown during exercise and these may be worthwhile considering for those seeking maximum protection;
• Diets – Avoid low- or reduced-carbohydrate diets such as the ‘Zone’ or ‘Atkins’ diet; as well as making you feel tired and lethargic when you train, they will do your immune system no favours!

Summary