Daylight Saving Time (DST) is the yearly practice of setting clocks forward one hour between the months of March and November. The idea behind DST is to conserve – or “save” – natural light, since spring, summer, and early fall days typically get dark later in the evening compared to late fall and winter days. The non-DST period between November and March is known as Standard Time.
The United States has officially observed DST since 1966. We set our clocks forward one hour at 2 a.m. on the second Sunday in March, resulting in one less hour of sleep that night. Then, at 2 a.m. on the first Sunday in November, we set our clocks back one hour. DST is often referred to as “Spring Forward, Fall Backward” because of when these time changes occur.
Adjusting the time by one hour may not seem like too drastic a change, but sleep experts have noted troubling trends that occur during the transition between DST and Standard Time. These include upticks in heart problems, mood disorders, and motor vehicle collisions. Furthermore, DST can cause sleep problems if circadian rhythms are not aligned with natural cycles of light and darkness. Some people also experience insomnia symptoms due to time changes.
Humans and other mammals are guided by circadian rhythms, which are 24-hour cycles that regulate sleep and other key bodily functions such as appetite and mood. These rhythms are largely dependent on light exposure. In order to reset each day, they must be synchronized with natural light-darkness cycles in order to ensure healthy, high-quality sleep.
The transition between DST and Standard Time is characterized by more morning darkness and evening light. This can essentially “delay” your sleep-wake cycle, making you feel tired in the morning and alert in the evening. Circadian misalignment can contribute to sleep loss, as well as “sleep debt,” which refers to the cumulative effect of not getting enough sleep on a regular basis.
Humans are most vulnerable to sleep deprivation in early March, as they transition from Standard Time to DST. One study found that the average person receives 40 minutes less sleep on the Monday after “Springing Forward” compared to other nights of the year. Researchers have also noted negative effects that occur during the transition from DST to Standard Time in November. In addition to sleep loss, people are at greater risk of mood disturbance, suicide, and being involved in traffic accidents during both bi-annual transition periods. However, experts suggest that long term, there is a reduction of accidents as more people drive home from work in daylight.
While many people adapt to time changes, some studies have suggested the human body never fully acclimates to DST. Rather, their circadian misalignment may become a chronic or permanent condition. This can lead to more serious health problems, especially for those who experience “social jet lag” because their demands at work or school take precedence over a full night’s sleep. Social jet lag has been linked to a higher risk of obesity, depression, and cardiovascular disease. The effects of DST subside gradually after a few weeks.
DST is associated with many negative outcomes and risk factors that some experts advocate for abandoning the system altogether in favor of a year-round time. They argue a permanent standard time is more in line with human circadian rhythms, and that this schedule would carry benefits for public health and safety. On the side of the argument, people in favor of DST argue that at least 70 countries around the world observe DST as it decreases energy consumption, reduces costs, and protects the environment. There is also evidence that crime rates decrease with the use of DST due to the lack of dark hours.
Arizona, Hawaii, Puerto Rico, and the U.S. Virgin Islands do not practice DST, and in 2020, 32 other states have pursued legislation to adopt DST as the permanent year-round time.
In the days and weeks leading up to time changes, you can prepare yourself for the adjustment by taking the following precautions: