Patterns of sleep
An editorial in Nature for 30 October draws attention to the fact that before the availability of electric light people were forced to make the most of the limited hours of daylight and that meant rising with the lark and stopping work at the going down of the sun. Those who wanted to achieve as much work as possible had no alternative.
Today, with all our artificial lighting aids, we are no longer obliged
to follow such a programme, and this has changed the working day for
many of us, and the patterns of day and night may be adjusted in accordance
with what we or our employers fancy is efficient. Sometimes we find ourselves
working in defiance of our natural circadian rhythms, which is not good
for our physical or mental health. We must pay more attention to our
body’s rhythm if we are to avoid undesirable lifestyles.
Our daily cycles of sleep and wakefulness, circulating hormone levels
and body temperature can vary dramatically between individuals. It is
considered usual to enjoy some eight hours of sleep between 11pm and
7am but individual preferences operate and circadian phases alter with
age and may be seriously affected by various conditions such as Alzheimer’s
disease and schizophrenia. Also, working conditions habits and the need
to concentrate on special tasks often call for changes in sleep. In the
same issue of Nature, Alison Abbott has summarised some aspects of the
circadian dilemma.
With the appearance of the phenomenon of jet lag in air travellers, attention
has been turned towards the role of melatonin in controlling body rhythms.
This hormone is secreted by the pineal gland during darkness, but its
level falls with the impact of light and the change affects the function
of the hypothalamus. With a healthy function, body temperature, cortisol
secretion and the onset of sleep or wakefulness vary regularly according
to habit under the control of time-keeping genes. In old age less melatonin
is produced, and sleep may therefore be disturbed. Exposure to bright
light during the day increases nocturnal melatonin and so promotes sleep.
Sufferers from Alzheimer’s disease often become active at night,
to the disadvantage of their carers. People with schizophrenia tend to
show a similar pattern.
It is recognised, too, that depression attributed to seasonal affective
disorder is something to be taken seriously. Appropriate treatment with
light may relieve the condition within a week, whereas pharmacological
treatment with antidepressants is far less effective. Working demands
in modern society unfortunately neglect the importance of circadian biology,
and night shift work, in particular, tends to be inefficient because
daylight exposure cannot play its normal controlling role. Academic studies,
too, suffer when due attention is not paid to circadian phenomena. Adolescents
pay most attention to evenings, and lack mental alertness in the early
morning, and critics have condemned the tendency in some countries to
begin school days at 7 or 8am. It is beginning to be recognised that
the effects of recent discoveries of circadian biology should be given
serious consideration by politicians and the agencies which they control.
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Most information regarding the materials used in mummification procedures in dynastic Egypt has been derived from ancient texts. Herodotus and Pliny the
Elder have described the use of the oil from the cedar tree. But later scholars
have argued that the preservative oils were in fact derived from the juniper
and not the cedar. Hitherto chemical analysis has not been undertaken to determine
the truth of the matter, but a report in Nature for 23 October describes the
use of gas chromatography to analyse the constituents of a sample of unused
embalming material dating from 1500BC discovered at a site in Deir el-Bahari
in Egypt. A team of German scientists prepared a methanolic extract of some
embalming material found near a mummy of the 18th dynasty and examined it.