Study finds brain immune cells shift around age 50 in ways tied to dementia risk

The brain's immune mix may tip around age 50 in a way that helps explain rising dementia risk with age, according to a new study covered by Fox News.

Teams from the University of California, San Diego; the New York Genome Center; and the University of California, Irvine analyzed postmortem hippocampus tissue from 40 neurologically healthy adults ages 20 to 95. The hippocampus handles learning and memory.

First author Nathan Zemke of the UC San Diego Center for Epigenomics told Fox News Digital the most striking change came after about age 50. The brain's resident immune cells, called microglia, appeared to be increasingly replaced by immune cells entering from the bloodstream. Microglia normally clear debris and respond to injury. The incoming cells carried stronger inflammatory signals.

Researchers said that shift may feed chronic inflammation linked to cognitive decline and neurodegenerative disease, including Alzheimer's. They also saw wear on cells that help maintain the blood-brain barrier, plus widespread DNA and gene-activity changes.

One practical angle, Zemke said, is that blood-derived immune cells are more reachable than cells already deep in the brain. In theory, scientists might one day tune those circulating cells to be more protective and less inflammatory when they enter the brain, offering a path that does not require operating inside the central nervous system.

The study is early. It compared different people at different ages rather than tracking the same person for decades, so it cannot prove a single cellular change causes Alzheimer's. The sample was small and limited to the hippocampus. Timing and extent varied person to person, suggesting brain aging is not identical for everyone. Zemke said he would not recommend medical or lifestyle changes based on this paper alone. The NIH-funded work was published in Science.