Disturbed sleep is a common depression symptomchaiyan Anuwatmongkonchai / Alamy A quarter of depression cases are caused by people’s body clocks being out of whack, a large study suggests. This newly identified “circadian depression” responds poorly to standard antidepressants, but might be eased by taking melatonin or adopting behavioural strategies, like going outside in the early morning sun. “The coordination of [your body clocks] underpins your mood, your metabolism, your concentration, your sleep-wake cycle and many other key factors,” says Ian Hickie at the University of Sydney. “When it’s well, you feel really well, you get up in the morning full of energy. When it’s off, you feel je...