Whether it’s too little or it’s poor quality, sleep disorders and risk of dementia have become increasingly linked, and scientists are racing to find out exactly how.

Sleep’s restorative properties are well known, and one of its roles is clearing out a build-up of beta-amyloid plaques in the brain – one of the two most common hallmarks of Alzheimer’s disease. And existing evidence draws a line between dementia risk and issues such as disrupted sleep, brief bouts of sleep deprivation and long-term insomnia.

Now, a new study has turned up some more bad news for those who struggle to nod off at night or take medication to do so, but also some surprising results for sleepers who wake during the night and don’t settle easily again.

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“We expected sleep-initiation insomnia and sleep medication usage to increase dementia risk, but we were surprised to find sleep-maintenance insomnia decreased dementia risk,” explained lead investigator Roger Wong, an assistant professor in the Department of Public Health and Preventive Medicine, SUNY Upstate Medical University, Syracuse.

Read more: New Atlas