People with fewer happy chemicals in their brain might be at greater risk of neurodegeneration from Alzheimer's disease, according to new research.
Of people with mild cognitive impairment, those with lower levels of serotonin—a neurotransmitter associated with positive mood, appetite and sleep—were found to have increased memory problems, the Journal of Alzheimer's Disease, a peer-review journal, published.
The study therefore revealed that participants who already had mild cognitive impairment (MCI) had already lost brain structures that transported serotonin.
Newsweek has reached out to the authors of the study for comment via email.
Alzheimer's disease degenerates the brain, eventually leading to the development of dementia. The disease is associated with the build-up of several proteins called amyloid and tau, which clump up into plaques and tangles, and affect the brain's functions. Around 5.8 million adults live with Alzheimer's disease and other dementias in the United States, according to the Centers for Disease Control and Prevention (CDC).
MCI is the stage before Alzheimer's fully kicks in, and is associated with forgetfulness, loss of sense of smell, and struggling to remember words. MCI may not always lead to full-blown Alzheimer's, but is often a precursor stage, meaning that it is an important stage for early interventions.
"The study shows that people with mild cognitive impairment already display loss of the serotonin transporter. This measure that reflects serotonin degeneration is associated with problems with memory, even when we take into account in our statistical model MRI measures of neurodegeneration and PET measures of the amyloid protein that are associated with Alzheimer's Disease," Gwenn Smith, a professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine, said in a statement published Thursday.
However, the authors stress that these results only show a correlation between lower serotonin transporter levels and memory problems in MCI, which does not necessarily mean that serotonin or lack thereof plays a role in the progression of MCI to Alzheimer's.
In the study, the authors performed positron emission tomography (PET) scans on the brains of over 90 adults with and without mild cognitive impairment between 2009 and 2022, looking at serotonin transporter levels and the amount of amyloid-beta protein (Aβ) in the brain. Amyloid is one of the protein structures that build up in the brain and cause dementia.
They found that patients with MCI had up to 25 percent lower levels of serotonin transporters in some regions of the brain, specifically those involved in executive function, emotion, and memory. They also had higher amyloid levels than the control group.
"The correlation we observed between lower serotonin transporters and memory problems in MCI is important because we may have identified a brain chemical that we can safely target that may improve cognitive deficits and, potentially, depressive symptoms," Smith said.
The researchers hope that they can further investigate how serotonin is linked to Alzheimer's in the hope that it could be targeted in the treatment of the disease.
"If we can show that serotonin loss over time is directly involved in the transition from MCI to AD, recently developed antidepressant medications may be an effective way to improve memory deficits and depressive symptoms and thus, may be a powerful way forward to slow disease progression," Smith added.