Switch to summer time disrupts body clock
As Europe prepares to move its clocks back one hour to winter time, good news comes from the EU-funded EUCLOCK project: our bodies' internal clocks generally adjust to this autumnal time change quite easily. The bad news is that the same cannot be said for the switch to Daylight Saving Time (DST) in spring, when the clocks move forward an hour. Although a quarter of the world's population lives in countries which observe DST, there have been very few studies into the impact of DST on physiology and behaviour. Our body's internal clock relies on daylight to stay in synchrony with the environment, and this sudden change in the timing of the dawn represents a significant disruption to that system. 'While we generally think that the time changes enforced by the DST transitions are 'only an hour', they have far more drastic effects if viewed in the context of the circadian clock's seasonal changes,' said Professor Till Roenneberg of Ludwig-Maximilian-University in Munich, Germany. In this latest piece of research, which is published in the journal Current Biology, Professor Roenneberg and his colleagues examined the sleeping patterns of over 50,000 people. The team and found that the timing of sleep on free days follows the seasonal of dawn under standard time, but not under DST. They then analysed in detail the timing of sleep and activity for eight weeks around the two DST transitions in 50 people. In this study, they also took into account each person's individual chronotype - whether they were 'morning larks' or 'night owls'. They found that both sleep and activity times adjusted easily to the switch away from DST in autumn, but that the timing of peak activity levels did not adjust to the onset of DST in spring. People with later chronotypes, who tend to go to bed later and get up later, were particularly badly affected by the change. 'Our results show that the human circadian clock does not adjust to the DST transition,' said Professor Roenneberg. 'This is especially obvious in the late chronotypes in spring when one looks at their daily activity patterns. Essentially, their biological timing stays on standard, winter time, while they have to adjust their social schedules to the advanced clock time throughout the summer. 'It is much too early to say whether DST has a serious long-term impact on health, but our results indicate that we should consider this seriously and do a lot more research on the phenomenon.'