Fatigue related to outdoor darkness

Living in England in the heart of winter can make for quite a dark time, literally. For a number of months the sun does not rise until after 8 AM and sets before 4PM.  Even  people who have lived in the country all of their lives will tell you that this has the effect of making it seem much later than it is in the evenings. There is no denying that the environmental darkness that we experience  an effect on our psychological state, and possibly our physical state as well. I recently experienced this first-hand after spending almost 2 weeks in South Africa on holiday, where the sun rose before 6 and set after 8pm. Upon my return to Oxford I immediately lost over 6 hours of sunlight with no jetlag (time difference is only 2 hours). I find myself asking for dinner around 4:30 in the afternoon because it looks like dinner-time outside, and simply getting more tired in the evenings.

But what does science have to say about all this? The science of how our bodies regulate themselves on a daily cycle is known as the study of circadian rhythms. And indeed, the concept of circadian rhythms is not just psychological, with changes in body temperature, gastrointestinal, endocrine, and respiratory functions affected. Metabolism is also affected (though whether that or my brain is more at work with my 4:30 desire for dinner is debatable). Popular topics of study with circadian rhythm scientists are jet lag, shift work (i.e. if you have to work nightly shifts), and seasonal affective disorder (SAD). All of these are instances where our bodies experience changes in environment from what is considered the norm.

Jet lag is easily explainable through the study of circadian rhythms. By shifting time zones, your body immediately senses the new environmental conditions, and gradually your rhythms shift to become in line with this. However, as the cycles take time to align, this is what results in the feelings of jet lag – with changes in behaviour and performance observed. Working the night-time shift is more difficult than switching time zones because it involves using the body against some of the environmental cues (sunlight) that normally govern its functions. In these instances other environmental cues, such as social interactions, become more important to try and shift the cycle. However, studies have shown that individuals who work these shifts do exhibit behavioural problems and social isolation, compared to those working normal shifts.

So how does this all play out with respect to the English winter? Well, in winter we get a conflicting set of cues. True, the time in which we experience sunlight diminishes, but our work schedules and social interactions with others stay on the same time scale, in effect, helping out where the environmental cues are now absent. The hypothesis is that our circadian rhythms are phase-delayed in winter as contrasted to summer, but this has not been conclusively demonstrated. Interestingly, much research has been done with special bright light therapies, in order to reduce the symptoms of SAD. While these therapies do generally improve symptoms, they somehow do not appear to be effected by when they are administered. This confuses scientists, who suspect that it might be having a “sophisticated placebo or expectation response” effect.

The general outlook of the English is to simply accept the situation as it is, and take the occasional winter holiday to Spain or Mallorca. But perhaps the finding that night-shift workers deal with the situation in better in older age, due to advanced coping mechanisms, is the most illuminating.

Disorders of the sleep-wake cycle in adults


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