Daylight savings and circadian rhythms

Much of the population is likely to feel a few days of jetlag after the end of daylight saving this weekend and the turning back of the clocks. Some have called for the end of daylight saving altogether, including some sleep scientists who argue that switching the clocks back and forth is detrimental to our health. Many argue a few days of ‘jet lag’ is a small price to pay for the social and health benefits of having extra daylight hours in summer.

The beginning and ending of daylight saving does put us temporarily out of sync with our biological clock, which is integral to maintaining the sleep-wake cycle. Our physiology and behaviour, right down to our cells and genes, are guided by this clock and our daily exposure to light.

The end of daylight saving is more of a challenge than the beginning of it because our biological clock finds this shift to an earlier time zone harder to catch up on than the beginning of daylight saving, which is a delay to our clock.

Our central biological clock in the suprachiasmatic nucleus of our anterior hypothalamus in the brain, has about 20,000 neurons. This clock is adjusted each day by light-sensitive cells in the retina.

Because our biological clocks innately tick along with a slightly longer than 24 hour-cycle, getting enough morning light is essential to keep our clocks ticking with a 24-hour period, and this means exposing our eyes to natural light in the morning (even for 15 minutes or so) without wearing sunglasses.

A stable and entrained clock is important for living well – physically and mentally. Chronic health conditions linked to irregular circadian rhythms include diabetes, obesity, depression, bipolar disorder, seasonal affective disorder and other sleep disorders.
We aren’t born with a fully formed biological clock – babies sleep in short bursts around the clock, and there is a fundamental change in our biological clock from that of a child's to that of an adult’s which occurs during adolescence. As most parents will know, teenagers tend to go to bed late and sleep in, often very late. It is not just laziness. It’s adolescence. There is research that shows the shift from sleeping in, to getting up earlier again, signals the end of adolescence.

There are valid scientific approaches to accommodating the delayed sleep phase disorder that most adolescents experience. One is to change the school timetable, to starting later, to allow for this.

There is some data to show learning and attendance is improved by later school times, but there may be a longer-term unanticipated consequence. Knowing they don’t have to get up early in the morning may encourage adolescents to stay up later, exposing themselves to more light at night, and sleeping in later and therefore getting less light in the morning. This is the opposite of what we need to maintain our circadian clock. The delayed sleep cycle may become a self-fulfilling prophecy.

What we do know is that young people are generally not getting enough sleep or enough morning light. An alternative (or complementary) approach to shifting school times is finding ways to ensure they can adjust their clocks to an earlier position by getting the light in the morning they need and avoiding light too late at night.

Why don’t many of us, not only adolescents, like Mondays? Maybe because we can get our circadian clock out of whack by staying up late on a Friday, sleeping in on a Saturday, staying out late Saturday night, and sleeping in on Sunday. Come Monday morning, you’re in effect on Sydney time and going to work with jet lag.

The daily adjustment of our biological clocks by light is complicated by our geographical location. Geography is on our side in New Zealand, where we’re close enough to the equator to be able to get a reasonable amount of natural light in the morning, even on a cloudy day. Those in countries further from the equator, particularly northern Europe, might need a dose of artificial morning light along with their espresso, to keep their clocks in check.

Ensuring we get enough light in the morning can have huge benefits for elderly people too, particularly those in residential care facilities, who often aren’t getting enough light exposure.

As we age, our eyes can need more light to ensure the clock is kept ticking with a 24-hour period. Work increasing the strength of lighting in residential care facilities and increasing people’s exposure to natural (morning) light has shown improvements in mood, mental health and even slows the progression of neurological disease.

But should we turn back the clock, and abandon daylight savings? Well, the idea gets attention every year because turning back the clock in effect gives the whole nation a few days of jet lag, all at once. Yet I’m not seeing anyone suggesting that people should stop travelling to different time zones because they’ll get jet lag. The people we should be concerned about are shift workers, who live with this type of jet lag all the time.