Home field advantage is a real phenomenon in sporting events like the Olympics, because athletes who cross more than five time zones have double to triple the likelihood of falling ill, according to a new study.

Researchers tracked 259 rugby players who were competing in a 2010 tournament that would take them to Australia, South Africa and New Zealand over a period of 16 weeks.
The players would experience time zone differences of two to 11 hours from their own.

Over the four months, 187 players reported 469 illnesses, but location made a big difference.

For matches played on home turf, before players travelled, the incidence of illness was 15.4/1,000 player days. The figure rose to 32.6/1,000 player days for matches that were five or more hours' time difference away. When players returned home, the incidence of illness fell back to 10.6/1,000 player days.

The researchers don't think air travel explains the differences, but rather the "arrival and location of the team at a distant destination," they wrote in the study that appears online in the British Journal of Sports Medicine.

Possible additional stressors could include changes in pollution or air quality, temperature, allergens, humidity or altitude, as well as different food, germs and even culture.