As most people in the U.S. prepare to turn their clocks back an hour when Daylight Saving Time ends Nov. 1, Houston Methodist ENT and sleep expert Dr. Ahmed Sam Beydoun has answers for commonly asked questions about what the shift means for the human sleep cycle.


Question: So, what is Daylight Saving Time, anyway?

Dr. Beydoun: Daylight Saving Time is simply a way of shifting our clock relative to the sun. In the spring, we move the clock forward one hour so that more of our daylight falls in the evening. In the fall, we move the clock back one hour and return to standard time. The biggest consideration for our sleep is that while clocks can change instantly, a human’s internal body clock cannot.

Question: Why does Daylight Saving Time mess with our sleep?

Dr. Beydoun: The way I explain it to patients is that we have two clocks. One is the clock on the wall; the other is the biological clock in our brain. Light and darkness strongly set that biological clock. When we suddenly move the wall clock by an hour, our work, school and meal schedules change immediately, but our body clock is still running on the old schedule. That mismatch is why people can feel sleepy, wake up at the wrong time or have trouble falling asleep.

Question: Why am I still tired after gaining an hour?

Because an extra hour on the clock does not automatically mean an extra hour of good sleep. Your body may still want to wake up at its old time, and the timing of light has also changed. And if you have been chronically short on sleep, one longer night won't erase that sleep debt. While the fall change is usually easier than the spring change, it is still possible to feel off for a few days.

Question: How long does it take our body to adjust to the time change?

Dr. Beydoun: There is not one exact number for everyone. With a one-hour clock change, many people feel back to normal within a few days, while those more sensitive to schedule changes may notice it longer. The fall change is usually easier because we are shifting later. The spring change is tougher because we suddenly ask people to fall asleep and wake up an hour earlier.

Question: What health effects can people experience in the days immediately following the time change?

Dr. Beydoun: For most people, the effects are pretty ordinary: sleepiness, reduced alertness, difficulty concentrating and sometimes changes in mood. But the biggest concern related to these effects is safety. If you are sleepy, your reaction time and attention are worse, and that matters when you are driving or doing a safety-sensitive job. Research has also found small population-level increases in some serious outcomes, particularly heart attacks and fatal traffic accidents after the spring change, although not every large study finds the same effect. The fall change generally appears less disruptive.

Question: Who tends to be most affected by the time change, and who should take extra precautions?

Dr. Beydoun: The people I worry about most are the ones who are already running on too little sleep, people with very fixed early-morning schedules, and people who already struggle with insomnia or a circadian rhythm problem. Anyone whose job depends on alertness - drivers, health care workers, pilots, people operating machinery - should be especially careful. And if you know even small schedule changes affect you, it is worth planning ahead instead of assuming you will just power through.

What can people do in the days leading up to the time change to adjust more easily?

Dr. Beydoun: The biggest thing is not to go into the weekend already sleep-deprived. Keep your sleep schedule reasonably consistent, get daylight during the day and avoid trying to fix everything with a huge sleep-in. If you know you are sensitive to the clock change, you can move your bedtime and wake time gradually - even 15 to 30 minutes at a time - in the direction of the new schedule.

 

For more information or to schedule an interview with Beydoun, contact Amy McCaig, manager of public relations at Houston Methodist, at 217.417.2901 or almccaig@houstonmethodist.org.