Posted: February 3, 2005

Science of Sport: Nutrition Advice For Athletes - Keeping Your Immune System Strong For Winter Training

By Monique Ryan, MS, RD

Cold and flu season are still lingering and with your training program switching into higher gear for the 2005 racing season, nutrition strategies for staying healthy remain a top priority. You don't want a viral infection to slow down your workouts and hamper your fitness, so that you can be race ready for this season. This column focuses on some nutritional strategies that you can practice in both your daily diet and nutrient supplementation, and specifically around training sessions in order to give your immune system a good boost.

From a nutritional perspective, it is key to prevent deficiencies and consume optimal amounts of nutrients that play an essential in maintaining a healthy immune system. Periods of heavy training are also associated with a depressed immune function and compromised immune function can be further aggravated by inadequate nutrition. The body's susceptibility to a respiratory infection can be elevated for 24 hours after a tough workout, and a demanding race can impair your immune function for one to two weeks. Combining training with school and/or work can overtax an endurance athlete's resources, stress your body and compromise your ability to fight infection. You are also likely to be exposed to individuals with a cold or the flu over the next few months. A strong immune system should result in fewer colds or viruses, and if you do get sick, recovery should be quicker.

Your Daily Diet and Supplementation

Because increased oxygen utilization during exercise can increase the production of free radicals (unstable molecules that can cause tissue damage at the cellular level), increased food intake and supplementation with antioxidants may enhance immune-system performance. One of the nutrients most commonly associated with preventing colds is vitamin C, which has a widespread reputation as an immune system booster. While a multivitamin mineral supplement easily provides the Daily Value of vitamin C, don't underestimate the importance of consuming good food sources of this vitamin. Endurance athletes can consume over three servings of fresh fruit daily and up to two cups of cooked vegetables daily for ample amounts of dietary vitamin C. Most research measuring the effects of high doses of vitamin C through supplementation have not shown additional protection to the immune system, though many athletes swear by their vitamin C supplements. What we do know is that a daily dose of 250 mg is adequate to your saturate body stores with vitamin C. Excellent sources of vitamin C include sweet peppers, citrus fruits and juices, strawberries, cantaloupe, kiwi fruit and broccoli.

Two South African studies have produced encouraging results regarding vitamin C supplementation. One study had athletes supplement 600 milligrams of vitamin C for three weeks before a 90 km ultramarathon. The supplemented runners experienced fewer upper-respiratory infections in the two weeks following the race. A following up study confirmed these results, though a recent study is not as encouraging. Athletes supplemented with 1500 milligrams of vitamin C for seven days before a 90 km ultramarathon did not demonstrate enhanced immune function or decreased oxidative stress. While there is limited data on the adverse affects of high levels of vitamin C supplementation, doses in excess of 1000 milligrams could result in some gastrointestinal side effects.

Regardless of your level of supplementation, sticking with a high intake of fruits and vegetables should pay off immune wise. They contain hundreds of phytochemicals that provide many preventative health benefits, and are also excellent sources of carotenoids that boost the activity of white blood cells called lymphocytes. Beta-carotene can also be converted to vitamin A in your body, an important nutrient for the immune system.

Other nutrients essential for a strong immune system include adequate intakes of zinc, iron, and vitamins B6 and B12. A good daily multivitamin and mineral supplement providing 100-percent of the Daily Values ensures adequate intake of these nutrients on top of a well-balanced diet. Megadosing with vitamins and minerals can often compromise the immune system, especially with excessive intakes of iron, is not advised as this could impair immune function and increase susceptibility to infection. While iron is an important mineral for endurance athletes, iron supplements should be taken as required with regular monitoring or iron status. Excess iron can increase inflammation in the body. Research on zinc supplementation and the common cold is split down the middle in regards to effectiveness. While there is limited evidence that zinc supplementation can reduce the severity or duration of a cold, it appears that zinc must be taken within 24 hours of the onset of symptoms to provide any benefit.

Vitamin E is also a popular antioxidant nutrient, but one recently published study has suggested that large supplemented doses may produce negative effects in athletes. Triathletes took an 800 IU dose of vitamin E for two months before competing in an Ironman. When compared to a placebo, the vitamin-E supplemented group experienced more oxidative stress and a greater inflammatory response. It is important to keep in mind that very high doses of antioxidants can produce a harmful pro-oxidant effect and potentially impair your body's immune-system response. Right now many experts consider a dose of 200 IU to be safe. Strict dieting and chronic inadequate calorie intake can also compromise your immune system.

Calorie balance and essential fatty acids

Rapid weight loss of greater than 2 pounds per week (an amount often recommended by many diet programs) can have negative immune effects. Consuming adequate calories is of course also beneficial for an athlete's recovery and energy levels. Poorly planned and low calorie diets can also be low in protein, which also compromises your immune system. Diets too low in energy can also result in inadequate intake of immune boosting vitamins and minerals.

Having the proper balance of fat in your diet, and choosing good fats can also give your immune system a boost. While a very high fat diet can compromise immune function, a very low fat diet does not provide adequate amounts of essential fat acids. Polyunsaturated oils that provide omega-6 and omega-3 fatty acids are good for the immune system. However, most North Americans consume enough of the omega-6 fats (if not an excess) and need to increase intake of the omega-3s. Walnuts, fatty fish, and flax, soy and canola oils are good sources of this healthy fat.

Nutritional strategies around training

Besides consuming a healthy diet and supplementing wisely, specific nutrition strategies around training are also beneficial. When your immune system is compromised from training, this effect is related to elevated concentrations of stress hormones. Nutritional strategies to boost the immune system around training sessions focused on reducing the stress hormone response, less disturbance in blood immune cell counts, and lower oxidative activity. Some of the most important nutritional strategies center around carbohydrate intake before, during, and after training- a familiar practice for endurance athletes.

So training with optimal stores of carbohydrate not only provide fuel for your workouts, but supports a strong immune system. Endurance athletes who train in the carbohydrate depleted state experience greater increases in the stress hormones that increase during exercise. Consuming carbohydrate before, during, and after endurance exercise seems to diminish some of the immunosuppressive effects of intense training. Carbohydrate intake before, during, and after training results in lower cortisol levels, fewer changes in blood immune cell counts, lower oxidative activity, and a diminished inflammatory response.

Overall, good dietary carbohydrate replacement in your daily diet that matches your training session (based on intensity and volume) supports your immune system. When you train for longer periods, the carbohydrate that you consume (usually in the form of a sports drink), also decreases some of the immunosuppressive effects of endurance training. After hard training, give your fuel stores a nutritional boost by consuming 50 to 75 g of carbohydrate afterwards, along with 10-15 g of quality protein to start the recovery process. This is especially important, as there is a window of at least several hours of depressed immune function after hard exercise. Try to stay away from individuals who have colds after hard training.

Of course managing life stress, getting adequate amounts of sleep also support a healthy immune system.

Monique Ryan, MS, RD, is author of "Complete Guide to Sports Nutrition," and "Sports Nutrition for Endurance Athletes," from VeloPress, and the upcoming "Performance Nutrition for Team Sports," (Peak Sports Press March 2005). She is a regular columnist for Inside Triathlon and VeloNews magazines, and is founder of Personal Nutrition Designs, a nutrition consulting company based in the Chicago area. Ryan regularly counsels endurance athlete across North America on performance and health-related nutrition concerns and offers online services through her website at www.moniqueryan.co. She was the nutritionist for the Performance Enhancement Teams for USA Triathlon and the T-Mobile Women's Cycling Team for Athens 2004. She also consulted with professional triathletes, the Saturn Cycling Team, and the Volvo-Cannondale Mountain Bike Team. Ryan offers answers to reader's questions twice monthly. Readers are welcome to send their questions directly to Ryan at RyanWebQA@aol.com. The information above does not constitute prescriptive nutritional advice. The information provided in this column is solely for general interest of the visitors to that site and is intended for educational purposes only.