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suprachiasmatic nucleus. They’re continuously updated by signals carried by hormones that circulate in the bloodstream, including one called cortisol.
Doctors and scientists now realise how important the body clock is to health and disease. Some drugs, like cancer chemotherapies, work best when given at certain times of the day, stem cell transplants can have different outcomes depending upon when they are given, and mental illnesses, including depression, schizophrenia and some dementias are often associated with poor sleep and tend to improve if the sleep– wake cycle is fixed.
There are also metabolic consequences of disrupting the body’s normal timekeeping. People who work night shifts are at higher risk of high blood pressure, strokes and heart disease and, amongst females, the risk ofbreast cancer increases. Researchers are currently trying to find out why this happens and one way to do this is to put volunteers into sleep experiments. One recent study was carried out by Harvard researcher Frank Scheer and his colleagues. 20
They placed 10 volunteers in a sleep study environment where they were denied access to watches or clocks and, unknown to the participants, the ‘days’ were made 28 hours long. This meant that over the 10-day course of the study the participants’ body clocks were progressively shifted until they were completely out of phase (equivalent to 12 hours jet lag), and then back into phase with their normal sleep–wake cycles. Throughout the study period, the team collected urine and blood samples and monitored the subjects’ blood pressures, metabolic rate and sleep quality to see how this affected the physiology of the participants.
The results were dramatic: levels of theanti-appetite hormone leptin fell by 17%, with the most pronounced drop at the 12-hour out-of-phase point, the glucose levels of the subjects were 6% higher and their insulin levels 22% higher. The average blood pressure was 3% higher, and the ‘sleep efficiency’ of the subjects was significantly lower – 67% versus 84% normally. Levels of the stress hormone cortisol, which should peak in the morning and fall during the day, were also reversed, leading to a surge in cortisol at the time when the subjects should have been going to sleep.
This shows that there are genuine and significant metabolic and biochemical effects associated with body clock disruption. And as Frank Scheer and his colleagues point out, discovering what causes these changes will help researchers to come up with effective ‘countermeasures’ to minimise the health impacts of shift work.

Chimpanzees carry the direct viral ancestor of HIV, the human AIDS (acquired immune deficiency syndrome) virus. This chimp version is called SIV (simian immunodeficiency virus) and is very similar to HIV except that, strangely, scientists have always claimed that, unlike untreated HIV in a human, SIV-infected chimpanzees don’t develop an AIDS-like illness and instead, infected animals live alongside the virus without getting sick.
    But new research, carried out in the African bush, has found that this claim is actually a microbiological myth and that chimp numbers in the wild – which are already dangerously low – are taking a significant beating at the hands of this virus. Brandon Keele, from the University of Alabama, Birmingham, 21 made the discovery when he carried out a long-term study on three free-living chimp communities in the Gombe National Park in Tanzania.

    Together with colleagues, he collected over 200 urine and 1100 faecal specimens from more than 90 chimps during a nine-year period. These samples were then used to look for antibodies as well as the genetic material of chimpanzee SIV. The team were also able to use genetic fingerprinting technology to identify and follow the progress of individual animals during the full nine years of the study. The results were strikingly at odds with the prevailing