How much you sleep one night depends on where you live in your time zone, suggests a new study.
And that, in turn, can help shape your overall health.
People living on the wrong side of a time zone see more sun later in the evening, go to bed later, sleep less and may have more health (and financial) problems.
Researchers from the University of Pittsburgh and the Universita della Svizzera in Italy found that people living on the fringes of a time zone where the sun goes down late have the greatest risks for breast cancer, obesity, heart attack and diabetes.
West each time zone go to bed later (dark blue), sleep less, earn less and suffer on average more diseases, as a map from the new study shows
Worrying that the US – and many countries around the world – are in an insomnia epidemic.
And falling asleep is a known risk factor for health problems.
Even small changes such as summer time are associated with higher heart attack rates.
We also know that women have higher breast cancer rates in women who work shifts.
Irregular working hours disturb the circadian rhythms of our biological clocks, which contribute to the fluctuations of our hormones.
However, the new study, published in the Journal of Health Economics, suggests that more small differences in our days and schedules can affect our sleep plans and health outcomes.
Going west, the sun goes on later and later in the day and even later within the time zone.
Within a time zone, the sun sets on the east side an hour earlier than on the west side.
Sleep experts say that the constant presence of artificial lighting has made it much more difficult for the average person to sleep than it once was.
Despite all this additional light pollution, the presence of the sun in the sky still has a strong attraction towards wakefulness or sleep.
The sun enters at a later time on the west side of each time zone (darker blue), as a map from the new study shows
. Light triggers a chemical that goes into the brain and tells us what time it is and what it should do – which is awake in the presence of light.
As long as the part of the brain of the biological clock, the hypothalamus, thinks it is daytime, it will instruct the endocrine to hold the melatonin, the hormone that triggers sleep.
The longer the sun emerges from this chain of events, the longer we stay.
Even if modern life does not suppose we have to get up early to work, at school and in the various other tasks of the day. As soon as the sun rises, the entire alarm system is released again.
The new study has shown just how accurate this movement is – and how powerful its effects could be.
The researchers compared the average daily sunset time data in each of the four time zones in the US with the average sleeping time of the individuals living in each county.
The average sleeping times per district only varied by about 20 minutes, ranging from 11:09 on the early side to 23:30.
But even this variation adds up quickly. If you fall at the late end of the bedtime spectrum, but at the same time (on average) get up like everyone else, you will lose 113 hours of sleep a year.
This variation was almost uncannily consistent with the shift in sunset times from east to west.
And another assessment just confirmed what the sleep scientist has long been saying about the negative effects of less sleep on health and economics.
In circles with late sunsets and bedtime, more residents had an average of six hours sleep or less, and more likely a full, luxurious eight.
In those high-light, low-sleep zones, obesity was 21 percent more frequent and people were overweight by 11 percent more frequently.
These combined risk factors also totaled higher rates of poor health outcomes.
Heart attacks, diabetes and breast cancer were also more common in the western end of the time zones.
These subzones are even more financially distressing, with wages three percent lower than the eastern sides of the time zones.
As a side note – or perhaps a consolation for the sleepless west – the authors of the study found that the term "work hard, play hard" can have ecological and biological foundations.
"Individuals can benefit more by enjoying more of the natural light in the evening," they wrote.
Whether this difference in quality of life is worth the lost wages, weight gain and disease was not discussed in the paper.
Instead, the authors encouraged people living on the wrong side of their time zone to try to balance their postcodes with social sleep schedules.