Sleep patterns and levels of the stress hormone cortisol could be used to predict which adolescents develop depression. It is known that adults with depression start having REM (rapid-eye-movement) sleep earlier in the sleep cycle than adults without depression but it is not clear whether the same relationship exists in adolescents. Researchers at the University of Texas Southwestern Medical Center studied 96 adolescents over five years and found that those with a familial history of depression but without a depression diagnosis started REM sleep earlier. Those who started REM sleep earlier in the sleep cycle were more likely to develop depression by the end of the five-year study than those who started it later. The researchers also looked into the effects of the stress hormone cortisol. In adults increased cortisol levels are linked to depression and when people are treated for depression cortisol levels are seen to fall even before people's symptoms improve. The study found that the teenagers with the highest cortisol levels at the start of the study were also more likely to develop depression.
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