One of my favorite books on the topic of sleep is Sleep Thieves by Stanley Coren
One chapter in the book deals with the history of DST (Daylight Saving Time) It also shows convincing data that moving the clocks one hour ahead, increases the risk of car accidents in the mornings by 6% for the first few days following the shift.
In 2008 the NEJM published a piece suggesting there is an increase of heart attacks as a result of DST
Other medical consequences include:
–An increase in appetite
–Fatigue and inattention
However one benefit may actually be an increased number of people exercising in the late afternoon / early evening.
On average it takes 3 to 5 days to reset the biological clock.
In Canada Saskachewan decided not to switch to DST; in the USA, Hawaii, Puerto Rico and the US Virgin Islands also do not switch to DST