LONDON—Here’sanewwarningfromhealthexperts：Sittingisdeadly.

Scientistsareincreasinglywarningthatsittingforlongperiods—evenifyoualsoexerciseregularly—couldbebadforyourhealth.Anditdoesn’tmatterwherethesittingtakesplace—attheoffice，atschool，inthecarorbeforeacomputerorTV—justtheoverallnumberofhoursitoccurs.Severalstudiessuggestpeoplewhospendmostoftheirdayssittingaremorelikelytobefat，haveaheartattackorevendie.

InaneditorialpublishedthisweekintheBritishJournalofSportsMedicine，ElinEkblom­BakoftheSwedishSchoolofSportandHealthSciencessuggestedthatauthoritiesrethinkhowtheydefinephysicalactivitytohighlightthedangersofsitting.

Whilehealthofficialshaveissuedguidelinesrecommendingminimumamountsofphysicalactivity，theyhaven’tsuggestedpeopletrytolimithowmuchtimetheyspendinaseatedposition.

“Afterfourhoursofsitting，thebodystartstosendharmfulsignals，”saidEkblom­Bak.Sheexplainedthatgenesregulating(调节)theamountofglucose(葡萄糖)andfatinthebodystarttoshutdown.

Evenforpeoplewhoexercise，spendinglongperiodsoftimesittingatadeskisstillharmful.TimArmstrong，aphysicalactivityexpertattheWorldHealthOrganization，saidpeoplewhoexerciseeveryday—butstillspendalotoftimesitting—mightgetmorebenefitifthatexercisewasspreadacrosstheday，ratherthaninasinglebout(一回)．

Still，inastudypublishedin2009thattrackedmorethan17000Canadiansforaboutadozenyears，researchersfoundpeoplewhosatmorehadahigherdeathrisk，whetherornottheyexercised.

“Wedon’thaveenoughevidenceyettosayhowmuchsittingisbad，”saidPeterKatzmarzykofthePenningtonBiomedicalResearchCenterinBatonRouge，wholedtheCanadianstudy.“Butitseemsthemoreyoucangetupandinterruptthissedentarybehavior，thebetter.”

FiguresfromaU．S.surveyin2003­2004foundAmericansspendmorethanhalftheirtimesitting，fromworkingattheirdeskstosittingincars.

Expertssaidmoreresearchisneededtofigureoutjusthowmuchsittingisdangerous，andwhatmightbepossibletooffsetthoseeffects.

“Peopleshouldkeepexercisingbecauset