Why do I wake up right before my alarm clock?

Q: Sometimes I wake up a minute or two before my alarm goes off. Is this normal? And why is my body doing this?

Little research has been done on how common this experience is and why it happens. But according to Russell Foster, head of the Sleep and Circadian Neuroscience Institute at the University of Oxford in Britain, many people think it’s “a real phenomenon.”

In one telephone survey published in 1997, for example, researchers from Iowa and Minnesota randomly interviewed 269 adults, mostly in the Midwest. About three-quarters of those interviewed said they sometimes woke up before the alarm went off, and just under a quarter said they woke up so reliably that they never had to use an alarm clock.

After the research team ran an ad in the newspaper asking about people who always or regularly woke up at certain times without using an alarm, they invited 15 of those respondents to a lab and tracked their sleep over three nights. They found that five out of 15 woke up within 10 minutes of their preferred wake-up time all three times.

Time is everything

No one knows exactly how or why the body is able to do this, but researchers say our biological clocks, which keep track of time, have something to do with it.

Just above the optic nerve in the brain is a master clock called the suprachiasmatic nucleus, said Dr. Ravi Allada, a neurobiologist specializing in sleep and circadian rhythms at Northwestern University.

This clock synchronizes and coordinates our body’s circadian rhythms, which help us prepare for things that happen at different times of the day, such as falling asleep at night and waking up in the morning.

One way our bodies do this is by sensing the light levels around us, said Dr. foster. Special cells in our eyes detect changing levels of light, such as just before and at sunrise — even through our eyelids when our eyes are closed, he said. These cells probably don’t tell our bodies exactly what time it is, but they can communicate that we are approaching the time when we normally get up.

This causes changes – like increase in hormones cortisol and adrenocorticotropin, as well as in blood pressure, said Dr. Foster – helping us prepare for activity.

What about the times you woke up right before your alarm clock when you had to get up much earlier than your body is used to, say to catch a flight or attend an important appointment?

Instead of waking up based on what time it is, Dr. Allada, our bodies can wake up based on how much time has passed since we went to bed – almost like an hourglass. If we go to bed knowing we have to be up in four hours, something can help make sure we wake up after four.

If things go wrong

If our bodies are so good at sensing time, why don’t we always wake up right before the alarm?

Dr. Foster isn’t sure. It’s possible that when you’re particularly tired, your body’s need for sleep overrides its biological clock, he explained.

Or sometimes, if you’re nervous about waking up on time, stress can cause you to wake up earlier than you’d like, said Dr. Allada.

it comes down to

There are still many more questions than answers about why and how our bodies sometimes wake us up before we sound the alarm.

But to maximize the chances of waking up on time, Dr. Foster said, it may be helpful to set your alarm clock for the same time each day, so your body gets used to waking up at a set time.