Can Exercise Improve Your Flu Immunity?

Unless you’ve been living under a rock for the last week,  you’ve heard of swine flu. It’s a new strain of virus that researchers think originated in pigs (aka swine.) As of right now the Center of Disease Control (CDC) has said the virus is a mix of four different flu viruses — “an unusually mongrelised mix of genetic sequences.”(1) This doesn’t sound good.

The problem, though, isn’t that this is a Frankenstein virus, but that nobody in the world has been exposed to this virus or any closely related version of it. No exposure means no specific (also called acquired) immunity against the virus. You see, your body protects you from the bad guys (germs, aka antigens like viruses and bacteria) in two ways:

1. natural (innate or non-specific) immunity or
2. acquired (adapted or specific) immunity. (2)

Your body’s defenses

Natural immunity is what you have going for you regardless of exposure to a particular bad guy such as a virus or bacteria. There are four main forms of natural immunity:

1. External defenses: Your skin, mucus, saliva, lysozyme in tears, acid in your stomach, cilia lined trachea, cerumen (ear wax), good bacteria on your skin and in your gut, other enzymes in mucus, all protect against everything from the outside without needing to know what exactly that is.
2. Viral sabotage: A group of small proteins called interferons (INF), so named because when a virus invades your body, your cells squirt out INFs that interfere with the virus by inhibiting viral replications (i.e., the virus can’t reproduce itself). Again no need to know exactly who the bad guy is.
3. Inflammation: You’ve probably noticed this immune response. During inflammation, histamine is released, which increases blood to the area and brings special cells (neutrophils and macrophages) to fight the virus.
4. Hand to hand combat: Well, it’s more like cell to virus combat. Special cells (neutrophils and macrophages) attack the virus and eat it (phagocytosis).

Natural immunity usually works pretty well, but has one major problem: it takes the body a while to figure out that it’s been invaded.

But with acquired immunity, your body can identify the bad guys very quickly and attack them before there are too many. It’s a bit like the FBI’s Most Wanted posters. Once the authorities know what the bad guys look like, they can catch them more quickly. This is the whole idea behind vaccinations. By letting your body get to “see” a weaker version of the bad guys it’s ready for action when the full strength version shows up.

If you look big and strong on the outside are you big and strong on the inside?

We’ve known for a long time that exercise helps you live longer and be healthier, but whether it makes you more resistant to catching a cold is a bit murky. Back in 1994, a group of researchers found that moderate exercise decreased your chance of getting an upper respiratory infection compared to no exercise, but beyond a certain amount your chance of getting an infection went up.(3-5) So there seems to be an optimal amount of exercise to combat sickness. Since then a handful of others studies have also found that same thing — a very good sign.

I want to make a point of this because it’s very important. Don’t believe a cutting edge, one-of-a kind study. Before you can feel confident about a study’s results you really need at least three separate labs reporting the same results. If you read a study and then never hear anything about it again or nobody else publishes something to support it then don’t believe it. That’s right — don’t believe it. I’m not saying anybody is doing anything wrong or inappropriate, but the underlying basis in science is independent verification — somebody else does the same experiment with the same results.

Think of a brand new scientific finding like a brand new recipe you find online. You might give it a try if you just find the recipe and see how it goes. But say your boss it coming over; wouldn’t you want a few testimonials saying they also tried the recipe and loved it?

This week’s review looks at exercise and getting sick in a slightly different way than previous studies. Instead of looking at infection rates (i.e. what are your chances of getting sick) they looked at how well you recovered if you got sick and if exercise helped.

Wong CM, et al. Is exercise protective against influenza-associated mortality? PLoS ONE. 2008 May 7;3(5):e2108. PMID: 18461130 [PubMed - indexed for MEDLINE]

Methods

This study was an epidemiological study.  That means they didn’t get a bunch of people sick with the flu and see who made it and who didn’t. What they did was collect information on how many people got sick from the flu in 1998, how many of those passed away, and general information on everybody.

Any exercise that was longer than 30 minutes, regardless of intensity, was counted. People were then grouped into three groups by exercise frequency: never/seldom (<1 workout /month), moderate (1 workout/month to 3 workouts/week) and frequent (four or more workouts/week).

Results

People who never exercised or exercised less than once a month had a 5.8% to 8.5% excess risks of mortality — i.e. chance of dying from the flu. People who exercised up to 3 times/week had a less of a chance of dying from the flu (4.2-6.4%). So a little exercise seemed to help. But more is not better. Exercising more frequently did not decrease the chance of dying from the flu compared to not exercising.

Conclusion

There seems to be an optimal frequency of exercise to fight off the flu. Moderate exercise (up to 3 times/week) decreased risk of death from influenza the most compared to little to no exercise. But too much (more than 4 times/week) wasn’t better.  However, more exercise didn’t make things worse than not doing anything.

Exercise has been shown to be beneficial to the immune system, but immediately post-exercise there is increased inflammation and a slight depression in immunity.(3) So, the idea is that if you work out more than 4 days/week your immune system has less than two days to recover between the next workout, which leads to less of an adaptation than exercising 3 days/week. For those of you that know about the theory of muscle adaption, it’s basically the same thing. You work out, which cause muscle damage, but also stimulates the muscle. If there is enough time between workouts the muscle recovers and overcompensates. If there isn’t enough time between workouts, the muscle doesn’t fully recover and either you don’t have increases in strength or you actually see loss of strength.

This study didn’t look at types of exercise or intensity of exercise and it didn’t separate people who worked out 4 days/week from those who worked out 7 days/week. Also, they had no idea what these people were eating. So for now, I’m going to keep working out 4 days/week, follow PN and if I start getting a rash of really bad colds I’ll think about working out less.

References

1. WHO statement on swine influenza
2. Rhoades, R. and Pflanzer, R. Human Physiology (3rd edition) Fort Worth; London: Saunders College; 1996: 832-836.
3. Nieman DC, Nehlsen-Cannarella SL The immune response to exercise. Semin Hematol. 1994;31: 166–179.
4. Davis JM, Murphy EA, Brown AS, Carmichael MD, Ghaffar A, et al. Effects of moderate exercise and oat beta-glucan on innate immune function and susceptibility to respiratory infection. Am J Physiol Regul Integr Comp Physiol. 2004;286: R366–372.
5. Lowder T, Padgett DA, Woods JA. Moderate exercise protects mice from death due to influenza virus. Brain Behav Immun. 2005;19(5): 377–80.