An excerpt from the article stresses that 'quality' sleep is a must too.
The less an individual slept, the more likely they were to develop a cold.
The quality of sleep also appeared to be important. Volunteers who spent less than 92% of their time in bed asleep were five-and-a-half times more likely to become ill than those who were asleep for at least 98% of their time in bed.
The researchers believe that lack of quality sleep disturbs regulation of key chemicals produced by the immune system to fight infection.
I guess this helps us understand a little more clearly the "The Korean Cold Wave" phenomenon that hits public schools regularly AND universities each semester . . . sigh.