Persistently worrying about the future or ruminating on the past can have a detrimental effect on cognition later in life, even increasing the risk of certain forms of dementia such as Alzheimer’s disease, according to a new study in the journal Alzheimer’s and Dementia.
The capacity of our thoughts to influence our physical health is something that is widely recognized yet poorly understood, with scientists largely unable to explain exactly how a person’s state of mind can alter their biology. Nevertheless, researchers have already come up with a theory known as the Cognitive Debt hypothesis, which states that certain negative thoughts and mental states somehow contribute to the risk of cognitive decline and dementia.
To test this notion, researchers spent two years analyzing the mental state of 360 people over the age of 55, paying particular attention to their tendency to fall into repetitive negative thinking (RNT) patterns. Participants were also assessed for depression and anxiety.
Results seem to be pretty unambiguous, with higher levels of RNT being strongly associated with cognitive decline across multiple domains, including episodic memory and global cognition – both of which are strong predictors of a person’s likelihood to go on and develop Alzheimer’s.
Brain scans were also performed on 113 of the participants, allowing researchers to observe the build-up of harmful protein plaques in the brain. Once again, high levels of RNT were associated with increases in a protein called tau in a brain region called the entorhinal cortex, which is often an early indicator of certain forms of dementia. Another protein called amyloid-beta is also strongly associated with Alzheimer’s and was found to be present in higher amounts throughout the brains of those with an increased tendency for RNT.
Study author Natalie Marchant sought to clarify these findings in a statement, explaining that while a long-term propensity for negativity appears to be a risk factor, episodic sadness in response to difficult life events should not be seen as something to worry about.
“Chronic negative thinking patterns over a long period of time could increase the risk of dementia. We do not think the evidence suggests that short-term setbacks would increase one's risk of dementia,” she said.
While the study authors aren’t entirely sure how RNT damages cognition in such a way, they speculate that the high-stress levels associated with this kind of thinking may be to blame. High blood pressure and the release of hormones like cortisol are both characteristic of stress and have previously been shown to stimulate the creation of tau and amyloid-beta proteins.
Based on these findings, the researchers suggest that meditation and other techniques that relieve stress and increase mental wellbeing may help to reduce the risk of dementia.