This week, it seems like everyone I know is snorting into tissues and sounding like Janis Joplin. Yep, it’s cold season again.
I confess I have a case of the sniffles myself. I can hear my mom telling me:
- Don’t go outside in the cold without your coat.
- Eat oranges and chicken soup.
- Get a good night’s sleep.
- Wash your hands!
You know, the usual mom-isms.
Was mom right about all those things? And did she miss one crucial piece — exercise?
Does being physically fit make me more immunologically fit?
The common cold
More than 200 viruses — mainly from two groups of viruses, rhinoviruses and coronaviruses — are responsible for the common cold.
Doctors call colds upper respiratory tract infections (URTIs), because that’s where the virus infects us. Your upper respiratory tract includes your nose, sinuses, pharynx (back of your mouth where you nasal cavity and throat meet) and larynx (aka voice box).
In the US each year, there are about 1 billion colds caught. Adults usually get 2-4 colds per year and kids get about 6-10.
I don’t know about you, but as an adult I’ve had stretches of years without a cold, so this 2-4 colds per year means either I have some super immune system or I’m doing something other average adults aren’t.
Exercise and immunity
A few studies suggest that there is an optimum amount of exercise to keep colds away — not too much nor too little.
Figure 1 below shows how moderate intensity exercise reduces the risk of getting an URTI (1).
After doing some sort of physical exercise, you end up with more immune cells (neutrophils and natural killer cells) in your blood, though it doesn’t last long. Really intense workouts produce more stress hormones (such as cortisol) that eventually suppress immunity (2-3).
Thus, moderate and regular exercise increases your immune cell count without triggering as much stress hormone release. You end up with a stronger immune system overall and you get fewer colds.
Unfortunately, research on immunity and exercise hasn’t had a very good way of telling how long or how bad the colds were. When did you start getting a cold? means different things to different people.
We also don’t know how much moderate exercise is best. After all, “moderate exercise” means different things to a couch potato versus a triathlete.
This week’s review study asks two key questions:
- Can being physically active protect you from the common cold?
- What level of physical activity protects you the most?
Nieman DC, Henson DA, Austin MD, Sha W. Upper respiratory tract infection is reduced in physically fit and active adults. Br J Sports Med. 2010 Nov 1.
This study included over 1,000 men and women between the ages of 18-85 years old. Participants were asked about various demographic and exercise-related factors, such as marital status, education level, sex, food intake, exercise frequency, how fit they thought they were, etc.
Then for 12 weeks, subjects filled in the Wisconsin Upper Respiratory Symptom Survey (WURSS), a survey used to track how often colds occur, and how bad they are.
Two graphs sum up this study. Figure 2A (upper graph) is a graph of the number of days that people had colds (upper respiratory tract infections) over the 12 weeks of the study, grouped into different categories.
Older people get fewer colds than younger people. People over 60 got 3.0 days’ worth of colds in a 12-week period on average, while people under 40 got 8.1 days.
Likely age is not the sole reason, but other age-related factors, such as older people not having young children (aka Nature’s little virus couriers), or being retired and not going to work where they would encounter sneezing coworkers.
The fitness level groups are what we’re interested in, but this isn’t measured fitness — it’s how fit people think they are (which may or may not be the same thing).
People who thought of themselves as being “very fit” got fewer colds (4.4 days) compared to people who said they weren’t fit (8.2 days).
Other things like education, marital status, gender, and fruit intake seemed to change the number of colds the participants would get. People who got more colds:
- were more educated;
- were single;
- were female; and/or
- didn’t eat much fruit.
So, any single PhD ladies out there, perhaps consider the Precision Nutrition system?
You may be wondering why these things matter. How, for instance, would marital status change your URTI risk? Should you start cruising the personals to save money on cough drops?
Just like age, it might not be a direct thing. Getting married isn’t going to increase your immunity like leveling up in World of Warcraft increases your stamina. Chances are if you’re married, you do other things that improve your immune system, or you may have more regular positive social interactions, all of which affect overall wellbeing.
Body mass index and URTI
Of all the results, the BMI results are the most difficult to understand.
Having a BMI between 25-29.9, which is considered overweight, results in the lowest number of colds (4.9 days). A BMI under 25 (normal) has the highest number of cold days (7.0).
If you look at the fitness results, where fitter seems to mean fewer colds, it gets even more confusing. It could be that the group with a BMI under 25 includes people that are underweight but not in a healthy way. They could be undernourished or have some kind of underlying medical problem, both of which may make them sick more often.
We don’t have enough information to say for sure, and the researchers didn’t mention what they thought was going on. I guess that’s a topic for another research review.
The second row graph (Figure 2B) looks at how exercise frequency (how often people exercise each week) affects the number of days people get colds. The more you exercise — up to a point — the better your immunity.
- Completely inactive people were sick for an average of 8.6 days for the 12-week period.
- Exercising at least once a week dropped the number of colds to 5.5!
- Exercising more than 5 times a week dropped the number of colds even more, to 4.9.
Based on this study, if you want to avoid getting a cold and/or shorten how long the cold will last, your best chance will involve:
- being over 60 years old
- barely graduating high school
- being married
- being male
- having a BMI between 25-29.9 (overweight)
- eating more than 3 servings of fruit a day
- having a low stress level
- exercising 5 times a week
- thinking of yourself as having a high fitness level
If you’re an old married guy with a little padding, who wasn’t much for book learning and now picks fruit on a nice relaxing organic farm for a living, you’re in luck!
Well, short of a sex change, a divorce, and sticking a crayon up my nose into my brain to remove the memory of all those additional years of higher education, I can’t do much about some of these factors. Some of those things, such as a higher BMI, may cause other problems.
However, I can eat more fruit, reduce my stress, and work out 5 times a week.
What if the only thing you change is exercising 5 times a week?
If you take all the factors out of the equation (control for confounders) and just look at physical activity and fitness, the most active and physically fit people got 43-46% fewer colds than less active and fit people.
Not only do you get fewer colds if you’re active and fit, but you get less severe colds with fewer symptoms.
Wait a second… that combination sounds like something that would help me lose weight and feel better in general!
In a world where there are constant trade-offs, it seems that exercising has nearly none and yet most of us are too busy to use this “too good to be true” option.
Moderate exercise (getting moving 5 times a week) decreases the number of days you will have a cold (if you get one at all) and how bad your cold will be.
Now bundle up and get moving!
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