Changing the clocks by an hour can disrupt your sleep and leave you tired for a few days. It can also throw off your circadian rhythm, your body’s internal clock.
Andrew Varga, MD, PhD, a neuroscientist and physician at the Mount Sinai Respiratory Institute Integrative Sleep Center, explains how the time change affects your body—and what you can do to help adjust.
“In our Sleep Disorders Program, we research, diagnose, and treat sleep issues such as insomnia, sleep apnea, and changes in circadian rhythms,” says Dr. Varga. “And we know that twice a year, everyone experiences a pretty dramatic shift in their biological rhythms because of the time change.”
How does the time change affect your body?
Any time change, including travel to another time zone, can force your body to adjust its internal clock. Your circadian rhythm is a roughly 24-hour cycle that responds to light and darkness. It helps control when you sleep and wake, along with other body processes.
When your body clock does not match the time on the clock, you may lose sleep and feel tired. The time change is also linked with increases in heart attacks, strokes, and car crashes caused by sleepy driving.
How long does it take to adjust?
It depends on how large the time change is and your age.
For a one-hour clock change, most people adjust within a few days. Larger changes, such as travel to Europe or Asia, can take about a week. Older adults may need two weeks or more.
What can help you adjust before bedtime?
“There are several things that I recommend to patients in my practice,” says Dr. Varga.
Take a low dose of melatonin.
I recommend a dose of 0.5 to 1 milligram of melatonin, at most, about three hours before the bedtime you want. If you want to go to bed at 11 pm, for example, take it between 7 and 8 pm.
This dose is much lower than many melatonin products, which may contain up to 10 milligrams. A low dose more closely matches the slow rise in melatonin your body normally produces in response to cues such as light, food, and physical activity.
I don’t recommend a higher dose for adjusting your body clock. Some people take higher doses to feel sleepy right away, but it’s not recommended for long-term use. If you have been taking melatonin regularly, especially at higher doses, I suggest to my patients to take a break and use it only when you want to adjust your body clock.
Cognitive Behavioral Therapy for Insomnia, a treatment that uses practical exercises and changes in thoughts and habits to support healthy sleep, may help during a break from melatonin.
Limit blue light at night.
After taking melatonin, try to reduce blue light. Avoid phones, tablets, TVs, and other screens when possible. If you still want to use screens, try a blue-light filter or blue-blocking glasses. The glasses can also reduce light from overhead sources.
What is blue light?
Blue light is part of the light that reaches your eyes. White light contains blue light along with other types of light. Many screens give off a higher share of blue light, even though you may not notice it.
Blue light is a strong signal to your body clock. That is why reducing blue light at night may help when you are trying to adjust your sleep schedule.
What can help you wake up after the time change?
“In the morning, light decreases the amount of melatonin in your body,” says Dr. Varga. “This is one of the cues, known as ‘zeitgebers,’ that help you wake up in the morning. To help this process, there are a couple of things I recommend to patients.”
Get plenty of blue light in the morning.
The morning is the time when you want plenty of blue light. I primarily recommend natural outdoor light, but if you awaken well before sunrise, I recommend blue-light boxes, therapeutic devices that emit small amounts of blue light, for adjusting the body clock.
If you travel often, especially between the United States and Europe or Asia, I suggest placing a blue light box on your kitchen table in the morning. You can eat breakfast or have coffee while the light shines toward your face for 20 minutes.
Use social and environmental cues
Light is the strongest cue that helps reset your body clock. But eating and exercise are other cues that can help your body know it is time to be awake. Morning meals and physical activity may help you adjust to the new schedule.