In 2025, Jingfeng Chen and a team from Chinese universities reviewed animal and human studies on how vitamin D and exercise together help keep brains healthy as people age. They looked at things like brain growth proteins, blood flow, and swelling in the brain, focusing on older adults with memory problems.

In 2015, J. R. Dalenberg and a team from Denmark conducted two field experiments with 30 students in dorm rooms. They tested ventilation by opening windows (low CO2: 660 ppm) or using a fan (low CO2: 835 ppm) vs. no ventilation (high CO2: 2,585 ppm or 2,395 ppm) for 1 week each. Sleep was tracked with wrist actigraphs, and next-day alertness via questionnaires and cognitive tests.