AT LAST. The holidays. Away from the day-in, day-out drudgery of the office, the commute, the cooking and cleaning, the getting up the next morning to do it all over again. Instead, a week of exotic pleasures lie ahead: sipping cocktails from faux coconut shells, while you bask on palm-fringed beaches planning the night鈥檚 adventures at Disco Club Paradise.
Naturally, this is the time when you keel over with a cold, the flu, or a bad case of the runs. This is the time when your face, normally so smooth and flawless, sprouts a cold sore that definitely won鈥檛 endear you to that tanned god or goddess you spotted in the souvenir shop. Perhaps life is out to get you-or perhaps it鈥檚 your own physiology.
But first, is our premise correct? Are people really more likely to get sick on holiday? 鈥淧eople talk about it a lot, but nobody has ever verified it scientifically,鈥� says Sheldon Cohen, a psychologist at Carnegie Mellon University in Pittsburgh. Nor are scientists rushing to do so: grant proposals entitled 鈥淓mpirical Investigation of the Holiday Sniffles Phenomenon鈥� would likely get short shrift from those who hold the purse strings.
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Up the nose
Still, decidedly unfrivolous data coming out of labs like Cohen鈥檚, lend some credence to the folklore. And where there are gaps in the working model of exactly how holidays make you sick-well, the scientists are willing to hazard a guess. They speculate that the holidays, plus the crazy weeks that so often precede them, expose us to new bugs, activate old, dormant ones, and, perhaps most significantly, weaken our immune systems.
The researchers are, of course, homing in on the famous 鈥渕ind-body connection鈥�. A plethora of studies have shown, for instance, that putting a mouse or rat through stressful times-by moving it to a new cage with animals it doesn鈥檛 know, perhaps-triggers a host of changes in immune cell activity. The animal鈥檚 T cells, natural killer cells and macrophages respond more sluggishly to foreign invaders such as viruses. And the number of immune cells in its blood, as well as their production of important immune-signalling proteins such as interleukin-2, plummets. With a weakened immune system, no wonder stressed-out animals are more susceptible to infections.
But what about stressed-out humans? In one study that is about to be published, Cohen and his colleagues squirted cold virus up the noses of 276 people. Those who鈥檇 been stressed for at least a month by marital and work problems were two-and-a-half times more likely to develop a cold than those whose lives were relatively stress-free. (Studies on short-term stresses, however, are more ambiguous; some show that immune functioning is depressed, some that it may actually improve.)
There are two big reasons why stress may have nasty effects on the immune system. First is that emotional upsets cause a key stress hormone, cortisol, to rush into the blood. The cortisol enters immune cells where it can alter the activity of genes such as IkB, suppressing the cells鈥� ability to fight invaders. Secondly, a stressed-out brain sends messages via sympathetic nerves to places where immune cells are plentiful, such as the spleen and lymph nodes. There, the nerve endings release yet another hormone, noradrenaline, and this, too, suppresses immune cell activity.
The mad dash to clear the in-tray before leaving town is not quite up there with a stress such as tending for a gravely ill spouse for years. But those last-minute frenzies may still take their toll, says Ron Glaser, a virologist and immunologist at Ohio State University in Columbus. 鈥淵ou need to get everything done before you go away, you鈥檙e spending a lot of hours, under a lot of stress,鈥� he says.
Another charming consequence of all this stress is that the normally quiescent herpesviruses that we all harbour may be activated. No one knows exactly how this happens, although the viruses clearly have the machinery needed to take advantage of stressed-out humans. The DNA that makes up the viruses contains regions that bind stress hormones like cortisol. The theory goes that the hormone streaming through one鈥檚 blood activates the viruses and gets them replicating, killing cells. Voil脿! an unsightly sore appears on your sunkissed kisser.
Bugs abroad
But none of this explains why we get sick after we鈥檝e actually left for our relaxing holiday in the sun, and not while we鈥檙e rushing about the week before. Could it be a simple case of misperception? 鈥淵ou tend to notice it more if you get sick on vacation,鈥� says Suzanne Felten, a neurobiologist at the University of Rochester in New York state. 鈥淚t鈥檚 particularly true if you can鈥檛 spend two minutes away from the loo.鈥�
The lag in actually feeling ill could also reflect the time viral and bacterial infections take to incubate. We may succumb to an infection during that stressful pre-holiday week, but the symptoms only manifest themselves later, while we鈥檙e unpacking our fluorescent-pink bikinis at Club Paradise.
Then again, whoever said holidays are relaxing? asks Felten. 鈥淭he first day of my vacation I drove 600 miles,鈥� she recalls. 鈥淭ravelling is stressful. Being in a new environment, as wonderful and exciting as it is, is also stressful.鈥� Excitement-happy excitement as well as the unhappy, stressful sort-releases cortisol, noradrenaline and adrenaline, which is also involved in immune suppression.
And don鈥檛 forget that mainstay of travellers鈥� tales, the new bugs we encounter once we leave home turf. Usually, 鈥渋t takes being exposed to a new bug to make you sick, as well as being stressed,鈥� says Esther Sternberg, head of research on neuroendocrine immunology and behaviour at the National Institute of Mental Health near Washington DC. 鈥淚t could be that in your own environment you鈥檙e immune to everything you encounter.鈥�
Many of these novel bugs, of course, will have greeted us before we ever touch down on foreign soil and start searching anxiously for the Club Paradise shuttle bus. The bugs will have been on the plane, whistling through the recirculated air from the noses of several hundred fellow holidaymakers.
And that鈥檚 not the only way that long flights compromise our health. Changing time zones causes jet lag and sleep loss which also weakens the immune system. Last year, psychiatrist Mike Irwin and his colleagues at the University of California at San Diego kept 42 volunteers awake until 3 am, just for one night. The activity of their natural killer cells, macrophages, and T cells fell, and in some cases remained depressed for at least two days.
So, in the face of all this, what can we do to reduce our chances of sniffling and sneezing our way through the holidays instead of eating too much, drinking too much, making fools of ourselves on the dance floor and haggling over souvenirs to take home to Aunt Millie? 鈥淏efore you go away, get good sleep,鈥� Glaser advises. 鈥淓at right. Tell those kids to behave themselves. And try to plan a nice, sane work week. Ha ha. Good luck.鈥�