A long-term US study has found that people who reported watching television very often in midlife later showed brain changes associated with Alzheimer’s disease and dementia. The findings matter because they suggest that the type of sedentary behaviour, rather than sitting alone, may be linked to poorer brain health; however, the observational research cannot show that television viewing caused the changes.

Researchers followed more than 1,700 adults for nearly 24 years and compared later MRI scans with reported television habits in midlife. Frequent viewers had smaller volumes in memory-related and Alzheimer’s-vulnerable brain regions, smaller frontal and occipital lobes, and more white-matter damage linked to small-vessel disease; they also had a 69% higher dementia risk than those who watched rarely or never. The associations were stronger in men, while sitting at work was not linked to the same adverse brain measures.