Study: Sleeping less than 5 hours, or more than 9, can lead to cognitive decline

Too lit­tle sleep, and too much, affect mem­o­ry (Har­vard Health Blog):

“A group of women tak­ing part in the Nurs­es’ Health Study were asked about their sleep habits in 1986 and 2000, and were inter­viewed about mem­o­ry and think­ing skills three times over a lat­er six-year peri­od. Devore and her col­leagues observed worse per­for­mance on brain test­ing among women who slept five hours or few­er per night or nine hours or more, com­pared with those get­ting sev­en to eight hours of sleep a night.

How might sleep affect mem­o­ry? Peo­ple who are per­sis­tent­ly sleep deprived are more like­ly to have high blood pres­sure, dia­betes, and nar­rowed blood ves­sels. Each of these can decrease blood flow inside the brain. Brain cells need a lot of oxy­gen and sug­ar, so blood flow prob­lems could affect their abil­i­ty to work properly…Another pos­si­bil­i­ty is a two-way street between sleep and mem­o­ry: sleep qual­i­ty may affect mem­o­ry and think­ing, and the brain changes that cause mem­o­ry and think­ing prob­lems may dis­turb sleep.”

Study: Sleep Dura­tion in Midlife and Lat­er Life in Rela­tion to Cog­ni­tion (Jour­nal of the Amer­i­can Geri­atrics Soci­ety). From the abstract:

• Objec­tives: To eval­u­ate asso­ci­a­tions between sleep dura­tion at midlife and lat­er life and change in sleep dura­tion over time and cog­ni­tion in old­er women.
• Results: Extreme sleep dura­tions in lat­er life were asso­ci­at­ed with worse aver­age cognition…For exam­ple, women sleep­ing 5 h/d or less had worse glob­al cog­ni­tion than those sleep­ing 7 h/d, as did women sleep­ing 9 h/d or more; dif­fer­ences were equiv­a­lent to near­ly 2 addi­tion­al years of age…Women whose sleep dura­tion changed by 2 h/d or more over time had worse cog­ni­tion than women with no change in sleep dura­tion. Sleep dura­tion was not asso­ci­at­ed with tra­jec­to­ries of cog­ni­tive func­tion over 6 years, which might be attrib­ut­able to short fol­low-up for detect­ing cog­ni­tive decline.
• Con­clu­sion: Extreme sleep dura­tions at midlife and lat­er life and extreme changes in sleep dura­tion over time appear to be asso­ci­at­ed with poor cog­ni­tion in old­er women.