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In March, most parts of the United States move their clocks forward by one hour. This event starts daylight saving time. Many other countries also change their clocks each year, though they might start and end at different times. When the clocks change, many people feel very tired and grumpy the next day. However, research shows that this sudden shift can also affect our physical health in real ways. Some studies have found an increase in serious health problems, like heart attacks and strokes, in the days right after the spring time change.
Fortunately, there are steps people can take to reduce these negative effects. Getting more morning sunshine is a key strategy. Light helps reset the body's internal clock, which is essential for healthy sleep. Understanding how this clock works helps us see why this time change matters so much for our well-being.
In the United States, daylight saving time starts on the second Sunday in March. At 2:00 a.m. on that date, clocks are set forward by one hour. This means we lose one hour of sleep that night. The time change reverses on the first Sunday in November, when clocks "fall back" to standard time. However, not every place in the U.S. participates in this change. The state of Hawaii and most of Arizona do not change their clocks in the spring. These areas, along with U.S. territories like Puerto Rico and Guam, stay on standard time all year.
Some people try to get ready for the shift by going to bed a little earlier for several nights before the change. However, this preparation can be difficult. A third of American adults already do not get the recommended seven hours of sleep each night. Finding extra time for rest can be a challenge. The loss of sleep time adds to the struggle of adjusting to the new schedule. Parents should be aware that children may also feel more tired during this transition.
The human brain has a master clock that is set by exposure to sunlight and darkness. This clock is known as your circadian rhythm. It follows a cycle that is close to 24 hours long. This rhythm controls when we feel sleepy and when we feel most awake. Our circadian rhythms change as we age. This is one major reason why young children who wake up early often turn into teenagers who struggle to get out of bed in the morning. The timing of their internal clocks shifts naturally as they grow.