Shift work
Working night shifts could have a negative impact on your health.

Night shift not only throws our body clock off the track, but may also damage our genes, according to a study by the Sleep Research Centre, UK.

The paper, published in Proceedings of the National Academy of Sciences, says that alteration of sleep cycle affects everything in our body, from hormones and temperature regulation to physical strength and normal brain function.

The research was carried out on 22 participants on a 28-hour day schedule, where they were weaned away from natural light and dark cycles.

Professor Derk-Jan Dijk, a co-author of the study, told BBC that every tissue in the body maintains a regular rhythm throughout the day, but shifts tend to disrupt the rhythmic patterns and natural synchronisation in body.

"It's chrono-chaos. It's like living in a house. There's a clock in every room in the house and in all of those rooms those clocks are now disrupted, which of course leads to chaos in the household," he added.

This disruption of circadian rhythm (body's 24-hour-cycle) also ends up interrupting the rhythm of genes.

"By disrupting sleep, and eating patterns, we are changing molecular processes by causing disturbances in the rhythm of genes," he told the Daily Mail.

He said that about 6% genes in our body have a circadian rhythm, which implies that their activity is selective to certain times of the day. Some of these circadian genes are active during the night and others during the day.

Blood samples from the participants showed a steady reduction in activity of the circadian genes over the 28-day period.

"Over 97 per cent of rhythmic genes become out of sync with mistimed sleep which really explains why we feel so bad during jet lag or if we have to work irregular shifts", Dr Simon Archer, a fellow researcher said.

"We think those triggered mainly by day could be concerned with the immune function and those at night are involved in regulating other genes," said Professor Dijk.

"Clock genes" are responsible for the circadian rhythm, as they code for "clock proteins". The levels of these proteins rise and fall through the day according to set patterns.

Growth hormone, testosterone and prolactin levels are diminished in the day time, but rise during night, while body temperature and blood pressure are seen to rise during the day, and fall at night.

It is well known that disturbances in sleep cycles cause negative health effects, but this study was one of the first steps in determining the variation in the activity of circadian or "clock" genes when the natural sleep cycle is interfered with.

"They show up after several years of shift work. We believe these changes in rhythmic patterns of gene expression are likely to be related to some of those long-term health consequences," said Dijk.

Diabetes, obesity

A separate study by the University of Pittsburgh School of Medicine interviewed over 1,000 retired night shift workers and found that people who regularly worked in night shifts were twice as likely to suffer from diabetes and had higher body-mass index (BMI).

Several other studies have linked night-shift work with impaired metabolic health and glucose metabolism, obesity, breast cancer and heart attacks.