It is the natural 24 hour body clock. We can work with our bodies and its circadian rhythms and feel the health benefits or work against it and suffer the health consequences.
We all have circadian rhythms – which is one of the reasons why we experience jet lag when travelling to different time zones.
This interesting recent journal article shows the health impact of disrupting the circadian rhythm in mice. This can be seen as a micro-representation of the effects which can occur to us http://ow.ly/oJcSd