Medical Matters: The changing of the clocks

By this time next week you will have two nights’ sleep under your belt after the clocks change at the weekend.

For most people the loss of an hour’s shut-eye is more than made up for by extended daylight in the evening time and the additional opportunities it provides for getting out and about.

But “springing forward” by 60 minutes can be hard on some people.

If you are someone who struggles with insomnia, the change can be enough to throw your sleep pattern completely out of kilter.

Successful insomnia treatment is largely based on getting those with the problem to adopt a regular sleep schedule; even an hour’s change can result in renewed sleep difficulty for some.

And night owls seem to have a greater difficulty adjusting to the spring time change compared with early birds.

Saving energy
Pushing clocks forward by one hour in spring to "daylight saving time" was first introduced in Germany during the first World War with the aim of saving energy and increasing productivity.

Its 1915 change was followed a year later by Britain, and soon Canada and the US had followed suit.

Largely reversed after the armistice, a different form of daylight saving was introduced in the UK during the second World War.

This time clocks were set two hours ahead of Greenwich Mean Time for the summer months.

Length of the day
For countries on or near the equator clock changes do not make any difference because the length of the day largely remains the same regardless of the time of year.

More recently there have been calls for the practice to be abolished.

Two arguments in particular are used: the effect of the change on road safety and its negative consequences for cardiovascular health.

A number of studies have found a link between the clocks going forward and an increased risk of heart attacks.

A 2012 US study suggested a 10 per cent increased risk of having a heart attack in the 48 hours after the clock changes in the spring.

Research from Sweden published in 2008 found a 7 per cent increase in the incidence of heart attacks in the first three weekdays after clocks went forward.

Sleep loss
It linked the finding with sleep loss induced by the loss of an hour as the clocks went forward. And both studies showed an equal percentage reduction in heart attacks in the corresponding periods in the autumn when the clocks were put back.

From a road safety perspective, the story is mixed. Canadian researchers found a 5-7 per cent increase in accident fatalities in the three days after clocks went forward at this time of year.

But a 2007 US study found that people walking in rush hour in the first few weeks after the clocks went back in the autumn were more than three times as likely to be involved in a fatal car crash compared with the weeks before the clock changed.

Time of day
The time of day mattered, with no effect seen at 12 noon, while the number of deaths rose at about 6 pm after the time shift.

Apparently the effect is not simply an issue of darkness, but more because drivers and pedestrians take some days to adjust their behaviour to the changed light. But overall there are fewer accidents during daylight hours.

Most of the health effects of time change can probably be linked to a phenomenon called circadian misalignment.

This is the difference between our internal clocks and the waking/
sleeping time dictated by work and family commitments.

Shift work has been linked with a higher risk of cardiovascular disease and breast cancer. And mood disorders, such as seasonal affective depression, are associated with exposure to natural light.

Personally, I would love to see the introduction of double summer time, during which we could enjoy even more evening light from next weekend, with clocks going back only one hour for winter.

mhouston@irishtimes.com
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