A study published in Sleep (where else?) suggest that poor sleep is linked to the genetic expression of depressive symptoms. Researchers studied 1,788 adult twins (because science is creepy sometimes), measuring sleep duration and depressive symptoms. Twins with a normal sleep duration (about 8.9 hours per night) only had a rate of twenty-seven per cent heritability of depressive symptoms. However, amongst those who slept too little (five hours per night), that rose to fifty-three per cent, and amongst those who sleep too much (over ten hours), the rate was forty-nine per cent.
According to the researchers, “These results are important because they suggest that sleep deprivation may be a precursor for major depression in adolescents, occurring before other symptoms of major depression and additional mood disorders.”