The risk of getting dementia may go up as you get older if you don’t get enough slow-wave sleep.

A 2023 study found that over-60s are 27 percent more likely to develop dementia if they lose just 1 percent of this deep sleep each year.

Slow-wave sleep is the third stage of a human 90-minute sleep cycle, lasting about 20–40 minutes. It’s the most restful stage, where brain waves and heart rate slow and blood pressure drops.