Benefits of Running:
How Running Can Boost Your Immune System
By Roy Stevenson

What do we really know about the health benefits of running? Can it really improve our health? Does being fit mean your immune system is more resistant to colds and flu infections? Do runners have a lower incidence of cancer? And if all this is true, how much running does it take to get these benefits?

Most runners blindly follow their training routines without knowing whether they’re doing the right amount of running to improve their health. In many cases, according to research, runners may actually be suppressing their immune system by working out too strenuously.

The rapidly growing body of research into the relationship between health and fitness, over 600 papers, show very positive and promising results. Running has some amazing benefits in terms of resistance to infection and certain cancers. It is clear that positive immune changes take place with moderate running. People who run (or exercise aerobically) at a moderate level experience fewer days of sickness from the common cold and other Upper Respiratory Tract Infections (URTI). What’s more, less competitive endurance athletes following lower key exercise regimens have enhanced immune reactions to infection.

One study found that women who walked briskly for 35-45 minutes, 5 days a week, for 15 weeks, experienced half the incidence of colds as the sedentary control group. A Runner’s World survey showed that 61% of recreational runners reported fewer colds since taking up running, and only 4% had experienced more colds.

Benefits of Running: How Light/Moderate Running Reduces Our Risk for Infection

Many studies indicate that exercising at a medium intensity level reduces our risk of infection over the long term. How does this happen?

Light or moderate running boosts our body’s natural immune system by circulating protective cells through the body faster, to attack and eliminate bacteria, viruses and fungi. Infection fighters, such as Natural Killer Cells, macrophages, immunoglobins, white blood cells, and other antibodies, are produced in the bone marrow, lungs, and spleen, and have a clean up effect on foreign invaders.

Another theory holds that the increase in body temperature when we run may inhibit the growth of bacteria, thus reducing its foothold in the body. Other exercise scientists believe that regular running helps rid the lungs of airborne bacteria and viruses that cause URTI, while others believe exercise causes the loss of carcinogens through increased sweat and urine loss.

Interestingly, active people also experience lower rates of colon cancer and breast cancer. Researchers think moderate exercise boosts the body’s immune system, attacking viral malignancies that have viral origin. It’s also thought that the faster passage of food through exerciser’s digestive tract reduces the contact time of carcinogens. And fit people are less likely to be overweight and have lower body fat, which can cause cancers.

However running can be a two-edged sword. Over-training can suppress normal immune function, so getting the right balance of frequency, intensity and duration of running or general fitness workouts is critical. Runners can easily go from vibrantly health and energy to toppling over the abyss, and picking up any virus and infections going around, if they overdo things.

Overtrained runners at all levels have been shown to experience impaired immune systems, to the extent that they suffer from a higher number of upper respiratory tract infections (URTI) than untrained people.

During Olympic Games, athletes experience URTI at abnormally high levels, according to clinicians. In the 1960 Tokyo Olympics, no less than 40% of the athletes were stricken with a nasty flu virus that swept through the games village like the plague—robbing many of medal performances. In the more recent 2000 Sydney Olympics, 33% of the New Zealand team’s visits to medical personnel were attributed to URTI.

URTI is also elevated following competitive endurance races such as marathons and triathlons. One in seven (14%) of marathon runners reported an episode of URTI during the week following the 1987 Los Angeles Marathon, compared with two in 100 (2%) of runners who did not compete.

It appears that the longer the endurance event, the harder the athlete’s immune system is hit. A survey of 140 runners in the 56K Comrade’s ultramarathon in South Africa found that 33% of the runners had symptoms of URTI, while only 15% of a control non-running group had symptoms.

According to research, there’s an “open window” of altered immunity, lasting from 3 to 72 hours after you run hard and for longer than 90 minutes. In this time, infectious microbes, viruses and bacteria may overcome your body’s natural defenses, depending on your natural state of immunity at the time.

Scientists notice that plasma levels of stress hormones such as cortisol and epinephrine go sky high after heavy running, as do anti-inflammatory cytokines. Natural Killer Cell activity, T lymphocyte levels, neutrophil function, and macrophage antigens all experience significant reductions after strenuous running.

The result of these myriad reactions is a cascade effect that can lead to depressed immune function in the exerciser or athlete who has been overreaching for extended periods of time.

The good news is that there’s no research to show that all endurance athletes doing intensified training are clinically immune deficient—we just happen to see more symptoms and higher URTI incidence among athletes from this population. For example, a 2007 study matching 32 elite triathletes with 31 recreationally competitive triathletes and cyclists, found a higher incidence of URTI illness in the elite triathletes than in the recreational triathletes.

Clearly there are more factors than just running that can affect our immune system and health. A person’s chances of getting URTI depends on other factors too—age, cigarette smoking, alcohol consumption, obesity, allergies, environmental conditions such as high altitude and extreme heat or cold, mental stress, other underlying disease, and lack of sleep, to name a few. A study of 852 German athletes found the combined effect of overtraining coupled with mental stress, lack of sleep and weight loss causes a higher level of URTI than even in overtrained athletes.

However, if you train hard but within your limits, your URTI risk is typically unaltered. There is a relationship between how much and how hard you exercise and your chances of getting infection. Exercise scientists have proposed the J-shaped curve theory to explain this interrelationship between exercise and infection. This curve shows that as you extend yourself into protracted, higher intensity training, your chances of contracting infection rises almost exponentially, compared with a person training at a moderate level.

Interestingly, despite the abundance of pills and potions sold in health food stores that claim to keep athletes healthy, there’s only one substance shown by research to positively impact the immune system—drinking carbohydrate solutions during and after endurance exercise.

Drinking one liter of typical sports drinks per hour has been shown to lower blood cortisol and epinephrine levels, reduce adverse changes in blood immune cells, and lower anti-inflammatory cytokine levels. This has major implications for runners, marathoners, triathletes, and other endurance athletes. The prudent runner will ensure that he has a sports drink before, during and after hard workouts.

Benefits of Running: How Much Running is enough to Boost Your Immune System?

Moderate aerobic activity of 30 minutes, almost every day seem to gain the most positive results in research. David Nieman, one of the U.S.A’s foremost researchers in exercise epidemiology thinks that walking or jogging at 70%-75% of VO2 max (or about 70% of maximal heart rate), for 40 minutes per day will give you half the chance of contracting URTI as non-exercisers.

Another study found that jogging 10 miles a week was beneficial to the immune system, but increasing it to 20 miles had an immunodepressant effect. Certainly doing more than 90 minutes of vigorous running points to an increase in URTI, so we should stay well below this level.

Elite runners and triathletes may be better off only doing one high intensity workout every 2-3 days, to ensure they are allowing for that 72-hour “open window” when they are more susceptible to infection following heavy workouts.

The American College of Sports Medicine has a well-researched position stand on The Recommended Quantity and Quality of Exercise for Cardiorespiratory Fitness in Healthy Adults that meets the requirements for enhancing the immune system quite nicely.

They recommend exercising 3-5 days/week, at 55%-65% of maximal heart rate, for 20-60 minutes using any activity that uses large muscle groups such as walking, hiking, running, jogging, cycling, aerobic dance/group exercise, rowing, stair climbing, swimming, skating and other endurance sports.

What can be done to minimize your chances of getting URTI?

Closely monitor your running to avoid overtraining and chronic fatigue.

Do not overdo high intensity training—runners who train and race at a faster pace have higher incidence of URTI.

Do not overdo long duration workouts—runners who train at 97 kilometers or more per week experience twice the URTIs compared to those training at 32 kilometers per week.

Use carbohydrate drinks before, during and after running events or during very heavy exercise sessions. Recommended dosage is 30 to 60 grams of carbohydrate during exercise. This will lower the impact of the stress hormones on your immune system.

Eat a well balanced diet to keep vitamin and mineral levels in the body at optimal levels. Important vitamins and minerals that have the greatest impact on immune function are vitamins A, E, B-6, B012, folate, essential fatty acids, the amino acids glutamine, arginine, and L-carnitine. No research has conclusively shown that ingesting these in supplement form reduces URTI, but taking them in amounts recommended for RDIs will not do any harm either.

Avoid large crowds of people for 1-2 weeks after you finish a marathon, an ultramarathon, or a triathlon. You’re more susceptible to URTI during this time.

Wash your hands with warm soapy water and minimize hand to eye and hand to nose contact, especially during cold and flu season.

Do not exercise in a group exercise setting if you have URTI, to avoid spreading it to others.

Get adequate sleep on a regular schedule. Sleep disruption has been linked to lowered immunity.

Keep your life stressors to a minimum because high stress levels have been linked to URTI.

What do you do if you contract a URTI?

Mild to moderate running when sick with URTI does not appear to be harmful. However, with symptoms of fever, extreme tiredness, muscle aches, and swollen lymph glands, wait 2-4 weeks before resuming your running program.

Avoid prolonged, exhaustive exercise during all stages of the common cold, regardless of symptoms.

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