For instance, older adults in high-income countries generally had lower rates of depression than their younger counterparts, while the trend was reversed in several poorer countries.

CNN: People in affluent nations may be more depression-prone

Bedrosian and her colleagues say that, among humans, exposure to artificial lighting at night has surged over the past 50 years, a trend that happens to coincide with large increases in depression prevalence.

CNN: Unplug! Too much light at night may lead to depression

Frieda Hughes has written about her parents and her own battles with depression but a family friend dismissed the idea that Nicolas's death fitted into a family trend.

CNN: Tragic poet Sylvia Plath's son kills himself

In the aftermath of the harshest economic downturn since the Great Depression, with banks still afraid to lend and small business owners afraid to borrow, that's an encouraging trend.

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