As people age, a certain amount of brain atrophy is expected. Shrinkage of the hippocampus is also associated with depression, dementia and Alzheimer's disease.
In the study, researchers asked 268 people aged 58 to 84 about their religious affiliation, spiritual practices and life-changing religious experiences. Over the course of two to eight years, changes to the hippocampus were monitored using MRI scans.
The researchers suggested that stress over holding religious beliefs that fall outside of the mainstream may help explain the findings.
"One interpretation of our finding -- that members of majority religious groups seem to have less atrophy compared with minority religious groups -- is that when you feel your beliefs and values are somewhat at odds with those of society as a whole, it may contribute to long-term stress that could have implications for the brain," Amy Owen, lead author of the study and a research associate at Duke University Medical Center, said in a Duke news release.
The study authors also suggested that life-changing religious experiences could challenge a person's established religious beliefs, triggering stress.