The brain may undergo a notable shift at midlife, as new research suggests that its protective immune cells begin to decline and are increasingly replaced by inflammatory cells at around age 50.Researchers from the University of California, San Diego; New York Genome Center; and University of California, Irvine, found that these brain changes may help explain why aging increases the chances of neuroinflammation and neurodegenerative disease, including dementia.The study analyzed postmortem tissue from the hippocampus – the portion of the brain that is responsible for learning and memory – in 40 neurologically healthy adults, ranging from 20 to 95 years of age.THE 'AGE' OF YOUR BLOOD COULD PREDICT DEMENTIA RISK, NEW STUDY SUGGESTS"The most striking change was that after about age 50, the brain’s resident immune cells, called microglia, appear to be increasingly replaced by immune cells that enter from the bloodstream," first author Nathan Zemke, Ph.D., principal investigator at the UC San Diego Center for Epigenomics, told Fox News Digital."Microglia normally protect the brain by clearing debris and responding to injury, but the incoming cells carry stronger inflammatory signals."The brain may undergo a notable shift at midlife, as new research suggests that its protective immune cells begin to decline and are increasingly replaced by inflammatory cells at around age 50.(iStock)The researchers believe this shift may contribute to chronic inflammation linked to cognitive decline and neurodegenerative diseases, including Alzheimer’s.They also noted the deterioration of cells involved in maintaining the blood-brain barrier – the protective filter that helps keep harmful substances out of the brain – as well as widespread changes in DNA and gene activity.'LONGEVITY GENE' MAY PROTECT THE BRAIN FROM ALZHEIMER'S BY BOOSTING DNA REPAIR, STUDY FINDSOne of the most exciting implications of the study, according to Zemke, is that the replacement immune cells origina...