Repetitive negative thinking may increase (or perhaps be caused by) cognitive decline and Alzheimer’s pathology

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Dementia: negative thinking linked with more rapid cognitive decline, study indicates

Demen­tia affects an esti­mat­ed 54 mil­lion peo­ple world­wide. There no cure, but reports indi­cate that approx­i­mate­ly a third of demen­tia cas­es may be pre­ventable, which is why many researchers have begun to focus on iden­ti­fy­ing risk fac­tors. This would allow for bet­ter per­son­alised inter­ven­tions that may be able to reduce risk, delay, or even pre­vent the onset of dementia.

Cur­rent research shows that genet­ics, high blood pres­sure, and smok­ing are all risk fac­tors for devel­op­ing demen­tia. But a lot of peo­ple don’t realise that there is also a rela­tion­ship between men­tal ill-health and high­er demen­tia risk too. Stud­ies have shown that depres­sion, anx­i­ety, and post trau­mat­ic stress dis­or­der are all linked to a high­er risk of devel­op­ing demen­tia in old­er age. Our recent study builds on this research by exam­in­ing whether a style of think­ing that is com­mon to these men­tal health con­di­tions is asso­ci­at­ed with indi­ca­tors of Alzheimer’s dis­ease, the most com­mon type of dementia.

Peo­ple expe­ri­enc­ing men­tal ill health fre­quent­ly engage in a style of think­ing called “Repet­i­tive Neg­a­tive Think­ing”. This style of think­ing involves the ten­den­cy to have neg­a­tive thoughts about the future (wor­ry) or about the past (rumi­na­tion), and these thoughts can feel uncontrollable.

In 2015, I devel­oped a hypoth­e­sis called “Cog­ni­tive Debt” which pro­posed that repet­i­tive neg­a­tive think­ing could be the “active ingre­di­ent” com­mon in all these men­tal health con­di­tions that may help explain the increased demen­tia risk we observe. Our recent­ly pub­lished study test­ed this hypoth­e­sis for the first time. We found that repet­i­tive neg­a­tive think­ing was indeed asso­ci­at­ed with indi­ca­tors of Alzheimer’s disease.

Our study looked at 292 old­er adults aged 55+ from the PREVENT-AD project in Cana­da. Their cog­ni­tive func­tion was assessed, mea­sur­ing mem­o­ry, atten­tion, spa­tial cog­ni­tion, and lan­guage. Of these par­tic­i­pants, 113 also had their brain scanned, which allowed researchers to mea­sure deposits of tau and amy­loid. These two pro­teins are bio­log­i­cal mark­ers of Alzheimer’s dis­ease when they build up in the brain. A fur­ther 68 peo­ple from the IMAP+ project in France under­went PET brain scans to mea­sure amyloid.

We found that peo­ple who exhib­it­ed high­er repet­i­tive neg­a­tive think­ing pat­terns expe­ri­enced more cog­ni­tive decline over a four-year peri­od. They also had spe­cif­ic declines in mem­o­ry (which is an ear­ly sign of Alzheimer’s dis­ease), and had more amy­loid and tau deposits in their brain.

We also exam­ined symp­toms of depres­sion and anx­i­ety. We found that both were asso­ci­at­ed with cog­ni­tive decline, but not with deposits of either amy­loid or tau. It may be that these symp­toms are more indica­tive of decline that hap­pens with age­ing or demen­tia that is not due to Alzheimer’s dis­ease. Equal­ly, par­tic­i­pants in this study had very low lev­els of depres­sion and anx­i­ety which would make it unlike­ly to be able to detect a rela­tion­ship. These find­ings do sug­gest that repet­i­tive neg­a­tive think­ing could one rea­son why depres­sion and anx­i­ety are asso­ci­at­ed with Alzheimer’s dis­ease risk – which is in line with my “Cog­ni­tive Debt” hypothesis.

How­ev­er, it is impor­tant to point out that although the hypoth­e­sis pro­pos­es repet­i­tive neg­a­tive think­ing increas­es risk for demen­tia (specif­i­cal­ly Alzheimer’s), the oppo­site may also be true. Peo­ple who expe­ri­ence a decline in their con­di­tion may become more con­cerned or wor­ried about their health – lead­ing to repet­i­tive neg­a­tive think­ing. Or, amy­loid or tau could have accu­mu­lat­ed in the brain, dis­rupt­ed its cir­cuit­ry, mak­ing it more dif­fi­cult to dis­en­gage from neg­a­tive thoughts. At this point we are unable to know which came first.

But how could our thoughts be asso­ci­at­ed with a dis­ease of the brain? On a bio­log­i­cal lev­el, neg­a­tive think­ing is asso­ci­at­ed with increased stress. In fact, repet­i­tive neg­a­tive think­ing is seen as a behav­iour­al mark­er of chron­ic stress by caus­ing ele­vat­ed blood pres­sure and high­er lev­els of the stress hor­mone cor­ti­sol. There’s increas­ing evi­dence that chron­ic stress is both harm­ful to your body – and your brain. But more research is need­ed to under­stand this link.

Giv­en that repet­i­tive neg­a­tive think­ing is respon­sive to treat­ments such as cog­ni­tive behav­iour­al ther­a­py or mind­ful­ness, future research will look at whether reduc­ing these think­ing pat­terns also reduces demen­tia risk. In the mean­time, there is evi­dence to sug­gest that many lifestyle habits – such as main­tain­ing a healthy diet, exer­cis­ing, and stay­ing social­ly active – are all linked with low­er risk of demen­tia. Although we don’t know whether reduc­ing repet­i­tive neg­a­tive think­ing could delay demen­tia in the future, tak­ing steps to look after your men­tal health is still impor­tant for your well-being in the present.

Dr Natal­ie Marchant is an Alzheimer’s Soci­ety Senior Research Fel­low based at Uni­ver­si­ty Col­lege Lon­don. She is cur­rent­ly involved in sev­er­al UK- and inter­na­tion­al­ly-fund­ed projects to inves­ti­gate lifestyle fac­tors that increase risk or resilience to neu­rode­gen­er­a­tion, cog­ni­tive impair­ment and Alzheimer’s dis­ease; and behav­iour­al inter­ven­tions that may mod­i­fy these fac­tors. Dis­clo­sure state­ment: Natal­ie L Marchant receives fund­ing from the Alzheimer’s Soci­ety, Euro­pean Com­mis­sion, and the Med­ical Research Coun­cil. This arti­cle was orig­i­nal­ly pub­lished on The Con­ver­sa­tion.

The Study in Context: