When time changes, so do we: The health effects of changing clocks

When the ‘-ber’ months roll around, everyone seems to have something to look forward to. The arrival of autumn, Halloween celebrations, Christmas festivities, or simply just the sense of another year drawing to a close.

For me, it’s the extra hour I get in bed when the clocks go back. But have you ever wondered why we change the clocks at all?

British Summer Time (BST), or Daylight Saving Time (DST), is the period in summer when the clocks are set forward by an hour from Greenwich Mean Time (GMT). In October, as we have recently experienced, the clocks go back again for the winter months. Benjamin Franklin, one of the founding fathers of the United States, first proposed the idea, but it was only taken seriously when a builder called William Willett campaigned in Britain to change the clocks. It wasn’t until the spring of 1916, during World War One, that the German army turned the clocks forward as a way of conserving energy – the UK followed suit. Ever since then, we’ve been changing our clocks twice a year.

When the clocks go forward, there’s maybe a 25% increase in the incidence of heart attack.

Dr John O’Neill

Today, opinions are still very divided. Some say that if the practice were to ever stop, dark mornings in the winter would become very unsafe. However, others say that changing the clocks twice a year disrupts our natural rhythm of sleep, leading to health problems such as strokes and heart attacks.

I think most of us can agree that the changing of the clocks brings about a sense of ‘seasonal jet lag’ – the tiredness, the grogginess, the mood swings. But on a serious level, one can observe something more dangerous: a disruption in our circadian rhythm (our body’s natural 24-hour cycle of physical, mental, and behavioural changes), also known as our body’s internal clock.

“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% increase in the incidence of heart attack.”

Scientifically speaking, when our internal clocks are misaligned, our blood pressure and heart rate increase which helps explain why studies have observed a small but notable rise in heart attacks and strokes in the days following the clock change.

So, when a sudden change occurs, even if you don’t feel the difference, vulnerable populations, such as the elderly or those with heart conditions, may feel the effects more acutely.

It isn’t only the heart that feels the effect; our mood and cognitive function are also disrupted. Here, we are talking about mental health issues such as depression and anxiety, immune function, sleep quality, and muscle strength. Surprisingly, there’s also a higher risk of car accidents.

O’Neill states: “The circadian clock regulates how able we are to maintain concentration. So, for a few days before the circadian clock has adjusted, people may be that bit more sleepy, that tiny bit more likely to have a lapse in concentration or reaction times.”

Left to themselves, our internal circadian clocks naturally align with the light-dark cycle

David Ray

Our circadian rhythm has been evolving over many years to respond primarily to sunlight, not numbers on a clock. The main signal our brain uses to synchronise our internal clock is sunlight. At night, or in darkness, failing light levels cause the brain’s pineal gland to produce the hormone melatonin, making us feel sleepy. In the morning light, our brain tells us to stop producing melatonin and start releasing cortisol to make us feel more awake. So, when the clocks change, this interferes with melatonin production, hence meaning darker mornings cause people to stir before they’ve had a chance to wake naturally.

“Left to themselves, our internal circadian clocks naturally align with the light-dark cycle, so the only problem comes if you start arbitrarily defining time based on a clock,” says David Ray, Professor of Endocrinology and co-director of the Sir Jules Thorn Sleep and Circadian Neuroscience Institute at the University of Oxford.

So, while many of us have been rejoicing at the extra hour we get in bed, it’s worth remembering that it subtly nudges our internal clocks out of sync. Perhaps it’s time to ask whether this twice-yearly disruption is worth the health cost, or if our lives would be better served by letting our natural circadian rhythms dictate time.