Your getting ready for bed probably starts before you’re even aware of it. Your body temperature drops by half a degree, and in response your pineal gland produces a surge of melatonin, a hormone that promotes sleep. But how far does your sleep pattern match what your body clock needs?
Your overall “body clock” is regulated by a region of the brain called the suprachiasmatic nuclei. During light hours this area of the brain suppresses the pineal gland’s production of melatonin. When darkness falls however the suprachiasmatic nuclei become less active and melatonin production resumes.
This is partly why looking at the television, smartphones and tablets can be so damaging to sleep. The quality of the light from them can keep the suprachiasmatic nuclei active, over-riding your internal body clock and stopping the release of melatonin. It’s the result of this disruption, rather than any brain activity, which makes it more difficult to get to sleep.
It’s also this link between our body clock and melatonin that makes it so difficult for shift workers to get enough sleep. At the very time they are trying to sleep their body clock is programmed for wakefulness, and the consequences of their not getting enough sleep can also be more serious than feeling groggy when they do go to work.
Shift work, and permanent night shifts, can have physical effects on the body. As well as an increased likelihood of injury compared to day workers, American studies also show shift workers have an increased tendency to metabolic syndrome, an early indicator of heart disease and diabetes. A 2012 study published in the British Medical Journal found that night shift workers had a heightened risk of heart attack and stroke, and emerging findings in 2007 saw the World Health Organisation declare shift-work to be a probable cause of some cancers.
Other research is showing that the effect of shift work and nights may only be half of the story about sleep patterns. As our body clock is governed by light it seems fair to assume that before the widespread availability of artificial light our sleep patterns must have been different – and it seems that they were. As late as the 18th century people talked about a first and second sleep, which were separated by an hour or two of wakefulness, a pattern which is also found in some pre-industrial tribal societies.
It’s the experience of geologist Michel Siffre in the 1960’s though that points towards an even older sleep pattern. Starting a two month research trip into a cave in Scarasson in July 1962 he decided not to take a watch or anything else that would enable him to gauge or estimate time. A little over what he thought was a month later Siffre was annoyed when his support crew got in touch with him only half way through the experiment, and was shocked to discover that eight weeks had in fact passed.
Whilst living in the cave Siffre’s body clock, in the absence of any daily cycle, had set itself at 48 hour days, with 36 hours of activity followed by 12 hour periods of sleep. Not only was this 48 hour cycle repeated ten years later when he stayed in a cave in Texas for six months, but it is also repeated elsewhere in nature. The Somalian cave-fish has evolved without eyes to live in the complete darkness of the caves below the Somalian desert. With no external stimulus its body clock is set at a 47 hour cycle.
Whether the true cycle for your body is to have a first and second sleep, or one twelve hour sleep every other day, one thing is clear – too little sleep or problems sleeping can have a major impact on your psychological and physiological health.
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