Indoor environment and brain health across the life course: A systematic review

Healthy indoor environments have been acknowledged as one of main determinants affecting brain health given much time spent indoors throughout the lifecycle. However, most studies were often restricted to categorical studies regarding specific indoor factors including indoor air pollutants, noise, lighting, temperature and dampness, and brain health outcomes. There were few studies that systematically indicated the connection between indoor environment and brain heath across the life course. We searched eight databases for studies on the association between indoor environmental exposure and brain health from inception to March 13, 2024. Of 18,735 retrieved records, 91 articles were included in our study. Exposure to indoor air pollutants in early life or childhood can lead to cognitive decline and behavioral issues, increasing the risk of ADHD. Continuous exposure to PM10 above 50 mu g/m3 increased ADHD and behavioral issues in children. Especially an increase of 5 mu g/m3 in PM2.5 concentration was associated with a 50 % rise in the risk of developing ADHD. Adolescents exposed to poor environment quality may experience diminished cognitive functions, behavioral problems, and mental health disorders. Long-term exposure to nighttime noise levels above 55 dB can increase the incidence of depression or anxiety symptoms in adolescents by 4 %-26 %. Similarly, prolonged exposure to NO2 over 26.5 mu g/m3 can increase a 1.62 times greater risk of schizophrenia. For the middle-aged and elderly, cognitive impairments, depression, and neurodegenerative diseases were closely linked to indoor environmental quality. Prolonged exposure to high concentrations of unpurified fuel smoke can impair cognitive function, whereas the use of clean fuels can reduce the risk of depression. Cognitive function in adults declined by an average of 5 % with each 6 degrees C drop or 9 degrees C rise in indoor temperature. In environments where PM2.5 levels exceed 25 mu g/m3, each additional 1 mu g/m3 of PM2.5can increase the risk of dementia in middle-aged adults by 55 %. The elderly were particularly vulnerable to prolonged exposure to PM2.5 levels above 10 mu g/m3, significantly diminishing their cognitive abilities. Poor indoor environment can have a direct or indirect impact on brain health by affecting the formation and release of neurotransmitters, neural plasticity and causing inflammation. This study will provide a basis to develop strategies for optimizing brain health at different stage of life.