Wednesday, 30 November 2011

Double summertime: Double trouble? Part 2

To determine whether we should the UK should have single double summertime (SDST) in the UK in this second blog post I will review large-scale trials of SDST. What effect that has had on the population health? I will also look at evidence comparing people in the same time zone: those living in the west, where the sunrises later in the day. Can the time of sunrise really impact our health?

Interpreting data over large scale trials is hard to establish, due to the amount of factors involved.When SDST was trialled in the UK between 1968-71 Parliament were unable to determine any clear benefits and reverted back to Britisth Summer Time.  One of the factors they were looking at was the rate of road traffic accidents. However, the introduction of a legal drink drive limit in 1967, and the first roadside breathalyser in 1968, made it difficult to determine the influence of SDST in the reduction in road traffic accidents. 

Breathalyser and the Drink Drive Limit reduced road traffic accidents in the late 1960s, obscuring any positive effects directly from the SDST trial (C) Isabelle Adam
Portugal, who are currently on the same time zone as Britain, moved to SDST in 1992, and soon moved back in 1996. SDST was unpopular in Portugal, despite the advantage of being on the same time zone as neighbouring Spain.

Portugal noticed the fall in children’s exams rates. The later light in the evening made it harder for the children to sleep, getting few hours sleep each night and causing their grades to fall. In my opinion, reduced performance at work would be a risk for most age groups, however children’s grades are the easiest to measure.

The Daily Mail reported that Portugal during SDST had an increase in insomnia, sleeping pill usage, and stress levels.

Will SDST increase sales of sleeping pills? (C) pinprick
The time of sunrise also impacts winter depression. Dr Michael Terman, an expert in circadian timing and depression, has researched the rates of winter depression in the US. He studied 5114 persons aged between 18-60 over 3 years across the US. His findings indicate that people further North, who receive less hours of daylight, are more prone to the "winter blues".

There's not a lot policy can do about the number of hours of daylight, but interestingly, the time of sunrise in this trial was also an important factor. Those living in the western edge of a timezone above 38 °N, where sunrises later than the eastern edge, have 26% more cases of winter depression[1].

The UK lies 50-60 °N, and this data provides a strong case for the UK not to enforce a later sunrise, and for further investigation to determine how the time of sunrise effects cases of winter depression in the UK.

The current bill requires a review of the success to be established; the effects on health such as rates of sleeping disorders and depression, sale of sleeping pills, should be clearly assessed as part of this. Also, research should be undertaken to understand the relationship between time of sunrise and rates of winter depression in the UK, before changing it.


[1] "Predictors of winter depression: latitude and longitude in relation to photoperiod and sunrise"
Terman, et al, Soc Light Treatment Biol Rhythms Abstracts 2008; 20:56

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