The link between sleep and dementia is two-way. And getting cause and effect is really hard to do. Because when you are developing dementia. And you can start to develop dementia, by the way, 20 years before it becomes apparent. You start to get the brain effects then. And what’s not known is whether or not that early development of dementia affects your sleep. Because certainly, when you’ve got dementia, your sleep is grossly disrupted. And people can just switch their daylight cycles sometimes – and they are up all night and they are asleep all day. So dementia itself affects your sleep.
Whether sleep itself causes dementia, I think is highly dubious. I suspect this comes from, the idea that dementia is a much longer disease than people think that it is. Some people even say that it starts in adolescence and you can track it through life. And it does affect sleep. But I think the causative effect is the other way: that dementia affects sleep, more than sleep affects dementia.
Dr Norman Swan, Physician and Journalist.