Whenever there is a pending change to or from Daylight Savings Time (DST), there is often discussion about the effects this will have on our sleep.  It is fair to say that there is generally less concern with the transition we are about to experience (from DST to Standard Time).  Most people simply don’t worry about it and look forward to an extra hour of sleep. 

Fewer adverse outcomes arise from the transition from DST, than the transition to DST*.  That said, changes in sleep and performance are still experienced.  These fall into two categories: (a) the changes we experience from the shift in the day/night cycle compared to the timing of our own internal body clock, and (b) the effects of our behavioural responses to transitions to and from DST.  This Sunday’s change from DST to Standard Time requires our body clock to shift an hour later**.  This shift is an easier one; our clock likes to drift later anyway.  However, the gradual seasonal changes we experience in the day/night cycle also help this along. 

Winter is a time of short daylight hours and long nights.  As we head out of winter, our daylight hours lengthen.  They extend at both ends of the day, which means to make full use of our daylight hours we would have to be up at 4-5am (simply not sensible for optimal daytime performance).  DST provides a way of shifting our daylight hours to be one hour later.  This transition means we shift our day/night cycle one hour forward in relation to our internal body clock.

Conversely, as we head out of summer and into winter, the days become shorter.  Suddenly, our change to a later day/night cycle means there is less light in the morning, so we opt to shift from DST back to Standard Time.  This gradual shortening of daylight hours, and the drift to a later sunrise, will lend a helping hand in coping with this Sunday’s DST transition.  Those of you who are lucky enough to wake without an alarm clock may have noticed that you have already begun to wake later.  Daylight hours have a profound effect on the timing of our internal body clock and consequently, our sleep.

The change from DST to Standard Time provides an opportunity to catch up on an hour’s sleep.  However, only those who are missing out on sleep will be able to sleep in***.  Catching up on sleep might have a positive effect by reducing sleepiness, and improving your cognitive and motor functioning.  For those of us who don’t want to sleep in, we will need to be aware that we will have a longer waking day than usual (approx. 1-hour longer).  Towards the end of our day, we will become sleepier, our performance will start to decrease and our risk of accidents will increase.

It is thought that behavioural changes may play a large role in the risk of sleepiness (and therefore, accidents) during DST change.  A transition from DST may mean that individuals who usually stay out late on Saturday nights choose to stay out even later.  Individuals may also stay out later on several nights preceding DST change in the knowledge that they will be able to catch up at the weekend.  Another consideration with Sunday’s DST change is the extra hour that needs to be fitted into the work schedule of shift workers.  Extended hours of work may also lead to sleepiness, and increase the risk of accident or injury.  If you have been up for longer than usual, or later than usual, make sure it is safe for you to drive home.

* I will save discussion about the change to DST for later in the year

** Give or take, depending on your recent sleep routine.  Additionally, our endogenous clock time is not 24-hours.

*** A good proportion of us are able to sleep in during DST change, what does this tell us about our sleep habits?