Boost Immune Function with Food

By USOC Sports Nutrition Team | Feb. 17, 2017, 2:02 p.m. (ET)

yogurt with blueberries 

The New Year’s resolution-related hype around detoxing is in full force at this time of year, but do detox or cleanse diets actually do anything? The short answer is a resounding no.                             

There is no need for anyone — athlete or not — to go on a commercial detox after the holiday season (or at any time of year for that matter). When athletes are training hard (as many are during winter training) or are exposed to environmental extremes (e.g. winter weather at northern latitudes), it places stress on the immune system, which can make it easier for foreign invaders to cause illness. Exposure to new germs through travel or being around large numbers of people also tests immunity. Making sudden, drastic changes (think “juice cleanses”) can compromise immune function even further, which is counterproductive given the already increased risk of getting sick during the winter time. So, why not focus on establishing a solid, healthy and sustainable routine, while boosting immunity the natural way?

A Closer Look at Vitamin C and its Roles in Immunity

The question of vitamin C supplementation comes up increasingly often at this time of year. People purchase vitamin C supplements when they have a cold, for protection against germs while traveling or for general daily prevention. Vitamin C’s role in immunity has to do with its antioxidant properties; helping to keep immune cells healthy so they can eliminate bacteria and viruses. Low intake of vitamin C can result in a compromised immune system, decreasing the body’s ability to fight off infection and disease. Due to its function in collagen formation, low vitamin C can also slow down wound healing and bone repair. However, just 10 milligrams per day (e.g. 1/2 tomato or 2 medium orange slices) is enough to counteract low vitamin C levels. Deficiencies are rarely seen in developed countries, and it’s highly unlikely for athletes to have low vitamin C levels unless they follow a very restrictive diet with no citrus fruits, juices or vegetables.

Vitamin C recommendations for athletes are the same as adults over the age of 19; 75 mg/day for women and 90 mg/day for men. Contrary to popular belief, taking high doses of vitamin C doesn’t prevent you from getting a cold; some evidence suggests supplementing with 500mg/day in the first 2-3 days following the onset of a cold may decrease the symptoms, severity and length. However, mega-dosing or consuming large quantities (>2,000mg/day) is not beneficial and can actually increase the risk of adverse effects such as gastrointestinal issues like diarrhea. There is no scientific evidence to date that supports any positive effect of vitamin C supplementation on sport performance, either. In fact, mega-doses of vitamin C can weaken training adaptations, since some inflammation is necessary for growth and recovery; it also causes vitamin C to act as a pro-oxidant, damaging tissues and cells. For these reasons, it’s recommended not to exceed 2,000 mg/day. One way to ensure you get just enough vitamin C, but not too much, is to choose food sources. Even in the middle of the winter, many of these foods are inexpensive and easily accessible.

Vitamin C: Pick Your Sources!

Food Item

Vitamin C Content (mg)

Percent of Daily Needs (%DV)

Red pepper, sweet, raw, 1 cup

95

158

Orange juice, 3/4 cup

93

155

Orange, 1 medium

70

117

Grapefruit juice, 3/4 cup

70

117

Kiwifruit, 1 medium

64

107

Green pepper, sweet, raw, 1/2 cup

60

100

Broccoli, cooked, 1/2 cup

51

85

Strawberries, fresh, sliced, 1/2 cup

49

82

Brussels sprouts, cooked, 1/2 cup

48

80

Grapefruit, 1/2 medium

39

65

Broccoli, raw, 1/2 cup

39

65

Tomato juice, 3/4 cup

33

55

Cantaloupe, 1/2 cup

29

48

Cabbage, cooked, 1/2 cup

28

47

Cauliflower, raw, 1/2 cup

26

43

*Recommended amounts are 75 and 90 mg/day for men and women, respectively.

**SOURCE: USDA Nutrient Database.


Tips to Reduce Risk of Illness and/or Boost Immune Function

  1. Wash your hands. This includes before and after eating, lifting, touching door handles, shaking hands, etc. Either soap and warm water or hand sanitizer works.
  2. Cover your mouth. Prevent spreading germs to others when you cough or sneeze.
  3. Stay hydrated. Our airways are the first line of defense against germs, so keeping them moist ensures optimal effectiveness. Dehydration also impairs the immune system.
  4. Eat a wide variety of colorful fruits and vegetables, whole grains, legumes, lean meat, nuts/seeds and dairy products or dairy alternatives. The simplest way to ensure you are getting what you need is to eat every two to four hours and focus on quality.
  5. Consume enough to meet training needs. Cutting out food groups or going long periods of time without eating (e.g. fasting) places unnecessary stress on the immune system. Eating enough means getting the right amount of carbohydrate, protein and fat, which also means increasing food intake during heavy training. If trying to lose body fat, do so slowly and gradually, and focus on maintaining a nutrient-dense diet (see point 4).
  6. Consider including some form of probiotic. There is evidence that athletes can enhance their immune function by consuming probiotics such as kefir, yogurt, kombucha, miso, tempeh, sauerkraut or probiotic capsules.

Detox the Natural Way

  1. Drink more fluids throughout the day, especially water. Aim for urine to be a pale yellow color; going to the bathroom about every two hours and having a normal urine volume are other easy ways to check in on hydration status. In the winter, tea, low to moderate amounts of coffee, soups and other hot liquids can contribute to fluid needs.
  2. Limit alcohol consumption, especially large amounts all at once. Alcohol is a literal toxin, and the liver must take time off from its normal duties of processing foods, storing energy and other important tasks in order to clear it from the body. One true way to detox the liver would be to avoid it!
  3. Increase fiber intake through consumption of whole foods. This adds roughage into the intestinal tract, which provides bulk for digestion and feeds the healthy gut bacteria that fight off pathogens.

To truly enhance immune function and performance this year, we suggest simply getting back to the basics and doing them impeccably well. Have a happy and healthy year!

Edited by Liz Fusco, MS, RDN, performance dietitian for U.S. Rowing National Team programs and consults with USA BMX, track cycling and triathlon.. For questions or inquiries, please contact Lfusco@usrowing.org.

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.