There’snothinglikeagoodnight’ssleep—butwhatdoesthatreallymean?Itturnsoutthattheanswerdependsnotonlyonyouragebutalsoonyourlifestyle.Somepeopleareproductiveandhappywithfewerhoursofsleepwhileothersn

　　There’snothinglikeagoodnight’ssleep—butwhatdoesthatreallymean?Itturnsoutthattheanswerdependsnotonlyonyouragebutalsoonyourlifestyle.Somepeopleareproductiveandhappywithfewerhoursofsleepwhileothersneedmore.Stillexpertscandetermineguidelinesthatworkformostpeople.TheNationalSleepFoundationresearchedthetopicandgavenewrecommendationsthisweek.Thefoundationacknowledgesthatsleepneedswillvary—lifestyleandstressshouldbetakenintoconsideration—buttheirrecommendationsofferageneralguideline.Forexampleteenagers(14—17yearsold)need8—10hours’sleepeveryday.

　　Tocreatetherecommendationssomesleepandmedicalexpertsreviewed312articlesfromjournalspublishedduringthelastdecade.Thisisthefirsttimethatanyprofessionalorganizationhasdevelopedage-specificrecommendedsleepdurationsbasedonasystematicreviewoftheworldscientificliterature.

　　Alackofsleepcanbelinkedtoweightgainbecausethatcausesanincreaseinappetiteaccordingtothefoundation.Itcanalsohaveseriousconsequencesonthebrain.Peoplewhodonotgetenoughsleepareatincreasedriskfordepressionandcanendangerothers.Thosethatbecomesleepywhiledrivingforexampleriskboththeirlivesandthelivesofthosearoundthem.

　　Researchersalsohavefoundinthepastthattoomuchsleepcanhavenegativeeffects.Lowsocioeconomicstatusanddepressionreportedlyaresignificantlyassociatedwithlongersleep.Howeverexpertsnowadaysfindthatresearchonoversleepingisstillunconvincingandneedsmoreattention.Currentlythereisnostrongevidencethatsleepingtoomuchhashealthconsequences.Thereishoweverlaboratoryevidencethatshortsleepdurationsoffourtofivehourshavenegativeconsequences.Weneedsimilarlaboratorystudiestodeterminewhetherlongsleepdurationsresultinphysiologicalchangesthatcouldleadtodiseasebeforewemakeanyrecommendationsagainstsleepextension.

　　56.WhichisTRUEaboutsleepingtime?

　　A.Experts’guidelineforsleepingtimeappliestoallthepeople.

　　B.Thetimeyouneedforsleepisrelatedtoyourstateofmind.

　　C.Thelessyousleepthemoreproductiveyouare.

　　D.Themoreyousleepthemoreener