Health and your body clock
13 May 2014 Last updated at 20:06 BST
Some doctors are beginning to prescribe drug treatments to follow the natural rhythm of our internal body clocks.
Everything from blood pressure to hormone levels fluctuate according to the times of day.
This 24-hour cycle affects alertness, energy levels and the chances of falling ill.
Fergus Walsh reports on chronotherapy, which matches treatment around patients' body clocks.