The advent of spring is associated with the prospect of increased sunshine, warmer temperatures and longer days. However, the enthusiasm for the start of British Summer Time (BST) is tempered by the inevitable clock change at the end of March. As the clocks sprung forward, our sleep may have been disrupted and we lost a valuable hour of our weekend.
Sleep patterns are determined by an interaction between the circadian clock, which drives daily, 24-hour rhythms in our physiology and behaviour, and the sleep homeostat which tracks the duration we have been awake as a build-up of the pressure to sleep. For the majority of us the clock runs at slightly longer than 24 hours and requires a daily correction to remain in sync with the external 24-hour day. Exposure in the morning to bright light – the most powerful influence on our internal clock’s timing – when we wake up can shift our circadian clock earlier in time to provide this daily adjustment. In contrast, bright light in the late evening has the capacity to shift the clock later in time.
As a nation we are chronically sleep deprived and the majority of us crave our “lie-in” at the weekend in an attempt to catch up on the missed hours of sleep in the preceding week. We’re also likely to stay up later on Friday and Saturday nights, safe in the knowledge that we don’t have an early start the following day.
This behaviour in itself is problematic as, by receiving bright light at later times in the evening and delaying the time we experience bright light in the morning, we are essentially letting our body clock shift later in time that is similar to flying one or two time-zones westwards. So, we will struggle both to fall asleep at our regular bedtime on Sunday night and again on Monday morning to wake up and get going because we are waking at an earlier time than our body is prepared for. It’s likely that many of us are experiencing at least a one hour time shift on a weekly basis as we transition from our weekday to weekend sleep pattern and back again.
Our delayed weekend sleep pattern means that this weekend we were not just shifting our internal timing by the one hour earlier necessitated by the switch from GMT to BST, but by the time we got to Sunday night we could have experienced the equivalent of flying two or three time-zones eastwards as we shifted to our weekday pattern.
It is possible to prepare your body for BST by gradually shifting the timing of your body clock in the days preceding the clock change if your schedule allows. So if for the three days before the clock change you progressively go to bed and get up 20 minutes earlier each day, and experience bright light upon awakening, then by Sunday your body will already be on BST.
The change from GMT to BST is unavoidable, but is counterintuitive in terms of our body clock and sleep patterns. In the first instance, moving the clocks forward results in delaying the clock time of sunrise and also then the time that we receive the morning bright light necessary to keep our body clock on track. Scheduling this time change for a weekend also compounds the problem as in order to correct for our weekend, a greater shift in internal timing is required to get us back on track for the week ahead. It is plausible that the clock change happening on a Friday night/Saturday morning, before we shift to weekend sleep timing, could help ease the transition to BST.
So today, make sure you order that extra shot of espresso and make some allowances for colleagues who arrived a few minutes late. You can blame the clock … the internal one that is.
Victoria Revell acts as a scientific advisor to light box manufacturer Lumie. She is a Postdoctoral Research Officer at University of Surrey