Olympic athletes submit their bodies to grueling training. And then they soar around the world to meet the competition. American east coast athletes traveled five time zones to get to London. West coast athletes leapt over eight. And increased the odds that they’ll get a cold, if not the gold. So says a study in the British Journal of Sports Medicine. [Martin Schwellnus et al., Illness during the 2010 Super 14 Rugby Union tournament—a prospective study involving 22 676 player days]

Researchers tracked 259 elite rugby players in the 2010 Super 14 Rugby Tournament. The 16 weeks of games took place in Australia, South Africa and New Zealand.

On average, there were 21 illnesses per thousand player-days. But players in their home countries endured only 15 illnesses per thousand days. And when a team traveled more than five time zones in either direction, illnesses rates more than doubled. The number dropped back to 10 after they flew back home. The illnesses were primarily infections, such as respiratory or intestinal illnesses.

A weakened immune system does not appear to be a factor. The researchers suggest that differences in temperature, pollution, allergens and different foods and local microbes are the likeliest culprits. One more element that might give European Olympians a home field advantage.

—Cynthia Graber

[The above text is a transcript of this podcast.]

[Interested in science and the Olympics? Check out the new Scientific American e-book, the Science of Sports: Winning at the Olympics. Available in most popular ebook formats including for the Kindle and the Nook. Just $3.99 wherever fine electrons flow or electromagnetic waves pass.]