Monday, 5 December 2011

Double summertime: Double trouble? Part 3

In this third blog post about single double summertime (SDST) I will respond to some of the supposed health benefits advocated by supporters of the lighter later campaign.

Dr Mayer Hillman, an active advocate of SDST, has predicted health benefits including, lighter afternoons might encourage more outdoor leisure pursuits leading to a reduction of obesity and related disorders[1]. 

However, these are assumptions on behavioural habits and there is currently no scientific evidence to support that an extra hour of light in the afternoon will be sufficient to increase outdoor exercise in the UK population. For those in London during winter the sun will set before 5pm, not significantly lengthening the daylight leisure time (map showing changes).

Will an extra hour of daylight encourage more outdoor exercise?  (c) Jon Candy
Hillman also suggests people will be exposed to more hours of daylight and are therefore likely to have improved mental wellbeing, more energy and lower rates of sickness. However, SDST will not increase the number of hours of daylight: it will only shift the timing of daylight hours to later in the day. In fact, deprivation of morning daylight is likely to cause the opposite effects: depression, sluggishness and higher rates of Seasonal Affective Disorder, SAD.

SAD, sometimes called the "winter blues", is thought to affect 2 million people in the UK. SAD in its most severe form can be debilitating, rendering sufferers unable to function during winter without treatment. It is often treated successfully with light therapy alone. The most successful treatment is morning light exposure from daylight imitating lamps, and is effective with over half of patients not requiring any other type of treatment[2]. This highlights how important quality, quantity and, crucially, timing of light is to our biology.

Lamps that simulate dawn are effective at combating SAD (C)  Susannah
In 2011 medical professionals at the British Medical Association annual conference rejected a bid to support SDST. There was a lack of categorical evidence for the supposed health benefits.

To achieve a healthier society, with increased productivity and performance, we need to encourage better synchronised body clocks. The health consequences of exposing ourselves to unnatural lighting conditions are being unravelled. Unnatural daylight hours are likely to intensify these detrimental consequences. 

Giving the proven importance of light in the morning on health, a policy that reduces morning daylight should not be supported on health purposes.

2.          Terman, M. & Terman, J.S. Lighttherapy for seasonal and nonseasonal depression: efficacy, protocol, safety,and side effects. CNS spectrums 10, 647-63; quiz 672 (2005). 

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