Shift work has 'chaotic' effect on genes

Shifting sleep patterns can dramatically affect the normal rhythm of gene expression, a study has found.

Like many animals, humans have a natural body clock, called the circadian rhythm. This regulates our sleep-wake cycles and metabolism, among other things.

By disrupting the normal sleep-wake cycles of 22 volunteers over a week, scientists at the University of Surrey showed a sixfold reduction in the number of genes being expressed in a rhythmic pattern.

'Over 97 percent of rhythmic genes become out of sync with mistimed sleep', says study author Dr Simon Archer from the University of Surrey. 'This really explains why we feel so bad during jet lag'.

The volunteers experienced 28-hour days, without the normal changes in light levels. Their sleep was delayed by four hours every day until they were 12 hours out of sync, meaning they were sleeping during the day. Blood samples were taken to test which genes were being expressed rhythmically.

The genes that lost their rhythm were involved in many important processes, such as normal gene expression and the circadian rhythm. Because these are general processes, changes in their expression could have further effects on many other biological systems.

Professor Hugh Piggins, who is a circadian rhythm researcher at the University of Manchester, and not associated with this study, told the BBC: 'The study indicated that the acute effects are quite severe. It is surprising how large an effect was noticed so quickly'.

Increasingly, shift work is being associated with enhanced risk of cancer, type 2 diabetes and heart attacks. Some studies have also linked disruptions in the circadian rhythm to illnesses such as depression (reported in BioNews 705).

'We of course know that shift work and jet lag is associated with negative side effects and health consequences,' says Professor Derk-Jan Dijk from the University of Surrey, who led this research. 'We believe that these changes in rhythmic patterns of gene expression are likely to be related to some of those long term health consequences.'

The results also suggested that changes in the expression of some genes was a result of the disrupted sleep pattern, rather than the body clock. This information could help in the search to understand the functional role of sleep.