Sitting at a desk all day or spending hours watching television may damage the brain in a way which is known to increase the risk of dementia, a new study suggests.

While researchers have known for some time that sedentary behaviour is bad for physical health, raising the risk of heart disease, diabetes and early death, it is the first study to show it could also influence mental wellbeing.

Scientists at the University of California recruited 35 people aged between 45 and 65 and questioned them about how many hours per day they spent sitting down over the previous week.

Each then underwent a brain scan to specifically look an area known as the medial temporal lobe which is crucial to the formation of new memories.