Every deductive leap comes with uncertainty in establishing a causal chain. I don't I'm being overly reductive about the nature of evidence when I say that.
There is a specific question that needs to be addressed: With a one week window into sleep habits, are we selecting for people who are chronically poor sleepers, with those poor sleep habits leading to disease?
OR
Are we selecting for people who are chronically ill for other reasons and those chronic illnesses prevent them from getting regular sleep?
For example, people with sleep apnea have terrible sleep, and they have lower life expectancy than the general population. However, the cause of that lower life expectancy is not the poor quality of sleep; it's the cardiac effects of abnormal breathing over a long period of time.
If a person with decades of excellent sleep habits developed sleep apnea in the last 5 to 10 years of their life, the accelerometer will capture their irregular sleep and the death registry will capture their early deaths. That doesn't mean poor sleep habits killed them.
There are many other such chronic illnesses that can be confounded this way. Heart failure. Obstructive lung disease. Dementia. All can lead to irregular sleep. Add them together and you've captured a large segment of the population with ~10 years left to live.
The authors address this relationship in the conclusion and supplementary materials, but they appear to approach it entirely from the framework of poor sleep being causative of cardiovascular disease. Well yes, there's evidence that poor sleep can cause cardiovascular disease, but it's also well established (as I explained) that it can happen the other way around. If you want to cement a full chain of causality, you need a longer time window. Capture a young population with a low burden of chronic disease, show that poor sleep habits came first (i.e. within a certain age window), then cardiovascular disease, and then shorter lifespan. That would be the ideal data, even if difficult to acquire.
There is a specific question that needs to be addressed: With a one week window into sleep habits, are we selecting for people who are chronically poor sleepers, with those poor sleep habits leading to disease?
OR
Are we selecting for people who are chronically ill for other reasons and those chronic illnesses prevent them from getting regular sleep?
For example, people with sleep apnea have terrible sleep, and they have lower life expectancy than the general population. However, the cause of that lower life expectancy is not the poor quality of sleep; it's the cardiac effects of abnormal breathing over a long period of time.
If a person with decades of excellent sleep habits developed sleep apnea in the last 5 to 10 years of their life, the accelerometer will capture their irregular sleep and the death registry will capture their early deaths. That doesn't mean poor sleep habits killed them.
There are many other such chronic illnesses that can be confounded this way. Heart failure. Obstructive lung disease. Dementia. All can lead to irregular sleep. Add them together and you've captured a large segment of the population with ~10 years left to live.
The authors address this relationship in the conclusion and supplementary materials, but they appear to approach it entirely from the framework of poor sleep being causative of cardiovascular disease. Well yes, there's evidence that poor sleep can cause cardiovascular disease, but it's also well established (as I explained) that it can happen the other way around. If you want to cement a full chain of causality, you need a longer time window. Capture a young population with a low burden of chronic disease, show that poor sleep habits came first (i.e. within a certain age window), then cardiovascular disease, and then shorter lifespan. That would be the ideal data, even if difficult to acquire.