Alzheimer's disease is not a pleasant diagnosis at the best of times, and now research suggests some of the early markers of the disease could actually be linked to our own, repetitive negative thought patterns.

The study looked specifically at 'repeat negative thinking', which isn't just the regular sad thoughts we all go through - it's defined as a cognitive process that encompasses our worrying and ruminating thoughts.

What the team found was that these obsessive negative thought patterns were linked to an increase in cognitive decline and aggregation of amyloid beta proteins – a brain protein that's involved in Alzheimer's disease.

It's important to note that this research is still in early stages, has quite a few caveats, and is observational. And correlation doesn't equal causation - there's no evidence here that ruminating negative thoughts are causing these early signs of Alzheimer's.

So, there's definitely no need to start thinking positive thoughts to try and prevent memory loss (although there are unrelated health benefits to reducing rumination).

But it's still an interesting study and if the research pans out, it could eventually give us a new way to test who could be at risk of Alzheimer's.

"Understanding the factors that can increase the risk of dementia is vital in helping us improve our knowledge of this devastating condition and, where possible, developing prevention strategies," explains the Alzheimer's Society Director of Research and Influencing, Fiona Carragher.

"The link shown between repeated negative thinking patterns and both cognitive decline and harmful deposits is interesting although we need further investigation to understand this better."

The researchers looked at data from a cohort study called PREVENT-AD – which included 292 people over the age of 55 who were in good physical and cognitive health, but had a parent or two siblings who had suffered from Alzheimer's disease.

The team also used data from 68 healthy adults from the Multi-Modal Neuroimaging in Alzheimer's Disease (IMAP+) study.

All of the participants completed something called a Perseverative Thinking Questionnaire (PTQ), which asked 15 questions focusing on rumination about the past and worry about the future.

They also conducted depression and anxiety tests to look at the overlap between RNTs and other mental health conditions.

The participants also underwent some pretty intense cognitive tests. The PREVENT-AD participants took 12 cognitive tests, which analysed things such as global cognition, immediate memory, delayed memory, attention, visuospatial cognition, and language.

"We found that higher levels of RNT were associated with more rapid decline in global cognition, immediate and delayed memory over a 48‐month period," the team writes in their paper.

"Further, RNT was associated with higher levels of tau in the entorhinal cortex (a region of early aggregation), and with global brain amyloid in two independent cohorts."

That sounds scary, but it's important to note that these are relatively small changes - for example, the mean score of the cognitive tests was 100 points, and the team found that global cognition declined less than half a point per year more quickly for each standard deviation increase on the PTQ.

Plus, those in the study were already at higher risk of Alzheimer's disease.

"Most of the people in the study were already identified as being at higher risk of Alzheimer's disease, so we would need to see if these results are echoed within the general population and if repeated negative thinking increases the risk of Alzheimer's disease itself," says Carragher.

The team itself also points out that we can't confirm if the negative thinking is causing the risk of Alzheimer's to go up, or the relationship is the other way around.

"Despite the Cognitive Debt hypothesis' proposal that RNT increases risk for Alzheimer's disease, the opposite may also be true. Amyloid beta and/or tau may aggregate first, disrupt neural circuitry, which then leads to a difficulty in disengaging from thoughts and elevated RNT," the researchers write.

They also explain that, ideally, RNTs would be measured multiple times to make sure the thoughts are actually long term, and someone isn't just having a bad day.

The nature of the PREVENT-AD study means that wasn't possible in the majority of the cases, but the team found those who did multiple questionnaires had similar results time and again.

This study isn't out of the blue though. There are a number of other studies showing that those with anxiety and depression can have a higher risk of Alzheimer's disease.

So, while there's no need for concern just yet, the team hopes that with more research, scientists could use levels of repetitive negative thoughts to measure Alzheimer's risk.

"The relatively high degree of variance in RNT levels in two independent populations indicates that the PTQ may be a useful tool to measure Alzheimer's disease risk in non‐clinical populations," the team write.

"Further replication of these findings along with development of established cut‐offs, sensitivity, specificity, and predictive value data must be performed before recommending an RNT questionnaire as a screen for inclusion of high‐risk participants in future clinical trials."

The research has been published in Alzheimer's & Dementia.

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Repetitive Negative Thoughts Have Been Linked to Early Signs of Alzheimer's Disease