Contemplating Causes of the Common Cold

My cold companions: Tissues and Giant Microbe hand sanitizer.

My cold companions: Tissues and Giant Microbe hand sanitizer.

The common cold. Rhinovirus. Call it what you will, it’s not pleasant to have. But here’s the difference between a scientist and just about everyone else: Instead of just sitting on my sofa surrounded by the corpses of dozens of tissues sacrificed in the battle against rhinovirus and moaning “why me”, I pulled up my laptop and set about determining what risk factors might have led to this. Ineffective hand-washing and a culture that encourages people to go out and about despite illness are the obvious culprits, but there are some fun psychological ones as well.

Our understanding of the psychological risk factors for developing a cold owes a great deal to the brave volunteers who let themselves be deliberately exposed to the rhinovirus in the name of science, typically in return for room and board while researchers observed them for symptoms. We can’t just let people sign up for a cold study and then go about their daily lives to see if they develop a cold, because too many variables might be involved: how often they wash their hands, how many people they interact with, whether anyone they interact with has a cold to begin with, what they eat, and so on. To be scientific about it, our brave volunteers usually take one psychological test or another, sniff a rhinovirus-laced nasal spray, and sit back and wait for symptoms.

This is how researchers determined, decades ago, that being stressed puts you at risk for developing a cold. For two days, some 300 adult volunteers were given physicals and questionnaires, before being given nasal drops with one of five different viruses or (for the presumably lucky ones) simple saline. After this exposure, they spent a week hanging around in special quarantine apartments with daily examinations for cold symptoms. My favorite piece of the study: Someone got to count how many tissues each person used. (I just emptied by second box in as many days, but I don’t know where that puts me on any official severity scale). The volunteers’ stress levels were calculated from their recent stressful life experiences (ranging from death of a family member to just trouble with a boss or even vacations, with different values assigned based on how stressful they seemed), their self-reported perceived stress, and their negative mood.

Stress was a very powerful predictor of developing a cold: Less than 30% of those with the lowest stress scores developed even a mild cold, while 50% of those with the highest stress did. This isn’t just about the symptoms, either, because the same pattern shows up in clinical levels of infection, with about 75% of the least-stressed and 95% of the most-stressed showing biological evidence that the viruses had made their way into their systems. Sadly, there is no mention of how the number of tissues used played out; perhaps no one was ultimately willing to create a graph with “number of tissues used” on the Y-axis. Or perhaps it was just because the rest of the evidence was so clear that recent stresses would make it more likely that exposure to a cold virus would turn into an infection.

Avoiding stress may help you avoid infection, but seeking out social ties may actually reduce the severity of a cold. Volunteers this time were paid $800 (I’m not sure that’s enough for me to deliberately risk a cold, even in the name of science, but ask again when the misery of my current experience has faded), and the questionnaires were about their social groups. Points were earned for each relationship such as family, neighbors and friends that they interacted with at least every two weeks. People who had more diverse social networks – that is, not just family or friends or neighbors but all of them – were less likely to develop colds than people who had less diverse social networks.  So knowing a lot of different people might mean you’re exposed to colds more often, but you may be less likely to make that jump from exposure to actual infection. It may also help if you have a “positive emotional style“, meaning that you’re more likely to think that words like “energetic”, “cheerful”, and “relaxed” apply to you than “hostile”, “unhappy”, or “tense”.

None of this directly helps me now. I haven’t felt particularly stressed recently, although I have been on the job market, secured a new job, and am in the process of hunting for a new home, so my life events might overrule my perceptions. My social network isn’t the most diverse, but I’m pretty sure I have a more positive emotional style; there’s no science behind how those things might interact, so I can’t say if one is more important than the other. Unfortunately, it’s a lot easier to predict what puts someone at risk in a lab than to clearly identify a cause or an origin of one individual’s current cold. It makes me wonder which we’ll develop first, a way to pinpoint the cause or a cure. Right now, I have to admit the cure would be more welcome.

ResearchBlogging.org
Cohen, S., Tyrrell, D., & Smith, A. (1991). Psychological Stress and Susceptibility to the Common Cold New England Journal of Medicine, 325 (9), 606-612 DOI: 10.1056/NEJM199108293250903

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