Is sleeping during the night important for health?

Sleeping times do not affect a person's health

Question: Is sleeping during the night important for health?
Position‹2 of 2: One need not sleep at night to be healthy
Argument: Sleeping times do not affect a person's health

Contrary to popular belief, it does not matter when a person sleeps

The argument

People aged 18 to 64 are advised to sleep for 7 to 9 hours each day, but it does not matter when we fall asleep. Our bodies engage in several activities while we sleep, from repairing cells to fighting infection and inflammation. To ensure that our bodies heal as we sleep, it is more important to sleep for the recommended number of hours per day than to sleep during the night. The time of day will not have an impact on our health as long as we have good quality sleep. Although countless people might argue that not sleeping at night can increase a person's chance of falling sick and eventually getting a terminal disease such as cancer, a recent study by Oxford University showed that there is no connection between getting breast cancer and working at night. Additionally, millions of people who work late night shifts have not gotten any terminal diseases, which supports the argument that one's bedtime does not influence overall health.

Premises

[P1]What matters for health is getting the recommended number of hours of quality sleep, not the time of day at which one sleeps. [P2] The body's restorative processes during sleep depend on sleep duration and quality, not on whether sleep occurs at night. [P3] Evidence such as the Oxford study on night-shift workers and breast cancer shows no link between sleeping at night and avoiding serious illness. [C] Therefore, one need not sleep at night to be healthy.

Counter-arguments

This understates circadian biology. A large body of research links night-shift work and circadian misalignment to elevated risks of metabolic, cardiovascular and some cancer outcomes — the WHO's cancer agency classifies shift work involving circadian disruption as probably carcinogenic. Hormones such as melatonin are governed by darkness, so *when* one sleeps, not only how long, affects the body's repair and regulation. A single study finding no breast-cancer link does not overturn that wider evidence, and 'millions of shift workers have not developed terminal disease' confuses the absence of an inevitable outcome with the absence of raised risk. Duration matters, but timing is not neutral.

Rejecting the premises

[Rejecting P3] One study and the survival of many shift workers do not show that sleep timing is health-neutral; broader evidence associates circadian disruption with elevated disease risk. [Rejecting P1] Melatonin and other restorative processes are tied to darkness, so the time of sleep, not just its length, bears on health.