CHANGE THE (BODY) CLOCKS

Why the end of British Summer Time can be a wake-up call for our circadian health

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Not to be all gothic and theatrical, but the darkness is coming. Come the end of October, the clocks go back. Suddenly, the Sun will set before 5pm and we'll walk around in astonishment as though it hasn't happened every year previously.

The shock is real, however; we feel it in our very cells. That's because the shift in our external clocks has an impact on our bodies' internal clocks, the circadian rhythms that underpin more aspects of our health and behaviour than many of us realise.

Most of us feel the clocks change with little more than seasonal jet lag. We're groggy and grumpy. At the population level, however, we see something more serious. Every October and March, there's a slight change in the incidence of heart attacks and stroke.

"It's more in March that the real problems arise, but going back is also not ideal," says Dr John O'Neill, who studies circadian rhythms at the Medical Research Council Laboratory of Molecular Biology. "When the clocks go forward, there's maybe a 25-per-cent increase in the incidence of heart attacks."