Scientists have discovered that the aging human brain may be far less isolated from the rest of the body than once believed. Stanford researchers found that large numbers of immune cells from the blood begin entering the brain as early as middle age, where they can transform into microglia, the brain’s specialized immune cells. The finding overturns a long-standing assumption that these cells remain largely separate from the body’s immune system throughout life.

Simply choosing the stairs could have surprisingly big benefits for your heart and longevity. A large analysis involving more than 480,000 people found that regular stair climbers were 39% less likely to die from cardiovascular disease and 24% less likely to die from any cause than people who rarely took the stairs. They also had lower risks of heart attack, stroke, and heart failure.

A surprising stress-related signal may help the brain repair itself after injury. Researchers found that myelin-producing precursor cells rapidly release the stress hormone CRH near damaged brain tissue, helping control how those cells mature and rebuild protective nerve insulation. The same system also influences brain development and the thickness of myelin later in life. The findings could offer new clues about how early-life stress contributes to psychiatric disorders.

Women who used estrogen-only hormone therapy later in life were less likely to develop dementia and showed fewer signs of Alzheimer’s disease in their brains, according to a large study of more than 21,000 participants. Hormone therapy use was linked to 39% lower odds of a dementia diagnosis and 35% lower odds of Alzheimer’s-related brain changes at autopsy, including amyloid plaques and tau tangles. Biomarker tests also suggested less amyloid buildup among hormone therapy users.

A large study of more than 5,500 adults over 50 found a striking combination of risk factors: abdominal obesity paired with vitamin D deficiency was linked to a 123% higher risk of death over six years. Each condition was associated with increased risk on its own, but together they appeared to create a dangerous feedback loop, with belly fat reducing the amount of vitamin D available in the bloodstream while low vitamin D may worsen inflammation and other health problems.