Depression Linked to Sleep?

I've just read an interesting article on BBC on the links between depression and amount of sleep.

In a study of 15,500 teens between the ages of 12-18 years, those who got less than five hours sleep per night were 71% more likely to suffer from depression.Of the 15,500 studied, those who went to bed after midnight were 24% more likely to have depression than those who went before 10pm.

Worse still, those who had less than five hours sleep a night were thought to have a 48% higher risk of suicidal thoughts compared with those who had eight hours of sleep.

The study published in the Sleep journal, was conducted by researchers from Columbia University Medical Center in New York and looked at data collected in the 1990s.