Both individuals get eight hours of sleep, which means they are sleeping for an adequate length of time. But one of them is sleeping at the wrong time, out of sync with the body’s biological clock.

Night-time is the body’s natural period for rest. This is the way nature intended it, and sleep tends to be of better quality at night.

As darkness falls in the evening, the body gradually begins preparing for sleep. The secretion of melatonin, the sleep hormone, increases during this period.

As light begins to enter the surroundings, melatonin levels start to fall again. Towards dawn, the secretion of cortisol increases. Cortisol is commonly known as the stress hormone and is associated with alertness and activity.

The combined effects of these processes influence the human body. Therefore, the quality of sleep is generally poorer for those who sleep more after daylight has appeared in proportion to his or her total sleep-time.

Moreover, daylight, noise and the activity of other people can all interfere with deep sleep. Sleeping at 10:00 pm generally allows for better-quality sleep than going to bed at 2:00 am.