Scientists may have uncovered a key reason why women tend to live longer and experience less cognitive decline than men. A recent study published in Science Advances suggests that women’s second X chromosome, previously thought to be inactive, may actually awaken later in life—helping to protect brain function.

Researchers at the University of California San Francisco found that in aging female mice, the extra X chromosome expressed over 20 genes, many of which support brain health. Notably, these genes became active in the hippocampus, a critical area for learning and memory.

Dr. Dena Dubal, lead researcher, noted that this “reawakening” of the silent X chromosome might help slow cognitive decline, which could explain why women’s brains generally appear younger as they age. These findings open the door to potential interventions that could enhance cognitive health in both men and women.

While more research is needed, this discovery provides new hope for tackling age-related cognitive decline and highlights the X chromosome’s untapped potential in brain health.