As people in the US prepare to turn their clocks ahead one hour in mid-March, I find myself bracing for the annual ritual of media stories about the disruptions to daily routines caused by changing from standard time to daylight saving time.
A third of Americans don't like the twice-yearly time changes. A majority of people would like to eliminate them completely.
The effects go beyond simple annoyance. Each March is connected to serious negative health effects.
The director of our sleep division is a professor of neurology and pediatrics at the University Medical Center in Nashville, Tennessee. My co-authors and I reviewed the evidence linking the annual transition to daylight saving time to increased strokes, heart attacks, and teen sleep deprivation.
My colleagues and I believe that the science behind the links is strong and that the evidence makes a good case for adopting permanent standard time nationwide, as I testified at a recent Congressional hearing.
Going from daylight saving time to standard time each November is relatively benign. Some people may feel thrown off balance and need a few weeks to recover, but research has not linked it to serious impacts on health.
Springing forward is more difficult on the body. Our clock time is moved an hour later, which makes it feel like 7 am, even though our clocks say it is 8 am. It is a permanent shift to later morning light for almost eight months, not just for the day or a few weeks after.
Morning light helps to set the body's natural rhythms and it wakes us up.
Light may have an effect on the stress response and the amygdala, a part of the brain involved in emotions.
Exposure to light later in the evening delays the release of melatonin, a hormone that promotes sleep. The effect can last even after most people adjust to losing an hour of sleep at the start of daylight saving time.
Adolescents are particularly vulnerable to sleep problems because puberty causes melatonin to be released later at night, meaning that they have a delay in the natural signal that helps them fall asleep. During puberty, melatonin shifts into our 20s.
School, sports, and social activity schedules can cause adolescents to be chronically sleep deprived. Many children start school at 8 am. Young people get up and travel to school in the dark during daylight saving time.
Daylight saving time affects people in different ways. A study shows that people living on the western edge of a time zone get less sleep than their counterparts on the eastern edge.
The study found that western edge residents had higher rates of diabetes, heart disease, and breast cancer, as well as lower per capita income and higher health care costs.
The western edge of a time zone has been found to have higher rates of certain other cancers.
Scientists believe that these health problems may be caused by a combination of chronic sleep deprivation andcircadian misalignment.
There is a mismatch between our biological rhythms and the outside world. The timing of work, school, and sleep is based on the time of day, rather than on the sun's rise and set.
Daylight saving time was instituted by Congress during World War II and the energy crisis of the early 1970s.
The idea was that having more light in the afternoon would save energy. This idea has been proved to be false, as heating needs can increase in the morning in the winter, while air conditioning needs can increase in the afternoon in the summer.
One of the pro-daylight saving arguments is that crime rates go down at the end of the day. The change is small and the health effects seem to outweigh the lower rates of crime.
Daylight saving time was set by state governments after World War II. The Uniform Time Act was passed in 1966 because of this. Daylight saving time was set from the last Sunday in April to the last Sunday in October.
Daylight saving time was expanded from the second Sunday in March to the first Sunday in November by Congress in 2007.
Daylight saving time is not allowed for states and territories. Hawaii, Arizona, and Puerto Rico are all on standard time. Many states are considering whether to stop falling back and springing ahead.
Should they pick permanent daylight saving time or permanent standard time?
Some Americans prefer standard time while others prefer permanent daylight saving time. The health-related science for establishing permanent standard time is strong according to my colleagues and I.
Standard time approximates natural light, with the sun overhead at or near noon. During daylight saving time from March to November, the natural light is shifted by one hour later.
Daylight saving time should be abolished and replaced with permanent standard time based on abundant evidence that it is not healthy.
Beth Ann Malow is a professor at the university.
This article is free to use under a Creative Commons license. The original article is worth a read.
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