NYTimes: The Claim: Lack of Sleep Increases the Risk of Catching a Cold.

From The New York Times:

REALLY?: The Claim: Lack of Sleep Increases the Risk of Catching a Cold.

As cold season approaches, many Americans stock up on their vitamin C
and echinacea, but heeding the advice on getting more sleep could be
more important.

http://www.nytimes.com/2009/09/22/health/22real.html