As reported by the New Haven Register, November 1, 2008.

Change Clocks, Not Sleep Cycle as Daylight Saving Time Ends

By Abram Katz

What happens to that hour that disappears between today and Sunday?

The day does not become 23 (and a fraction) hours long when daylight saving time ends.

Rather, the human time line is unstuck and re-pasted an hour earlier. As a practical matter, the sun comes up an hour earlier — otherwise known as the normal time.

“This is the glorious change!” said Dr. Daniel McNally, director of the sleep disorder center at the University of Connecticut Health Center. “We get an extra hour of sleep.”

This relatively minor shift can help people catch up on sleep and reset their biological clocks.

Get up at the same time as always, and you’ll be helping your locus ceruleus, dorsal raphe, suprachiasmatic nucleus, and the other chronological bits of gray matter that keep you synchronized with the rest of the world, McNally said.

Swedish researchers at the Karolinska Institute also found that the risk of having a heart attack decreases slightly the Monday after the end of daylight saving time.

What this means, if anything, is not clear, McNally said. The effect may not even be statistically significant.

But what it does show is that the brain and body are exquisitely tuned to daylight and dark, he said.

“The average person is sleepy and can use an extra hour of sleep,” he said.

Part of the reason for this torpor is artificial lighting, which pushes sleep back.

Before light bulbs, fluorescent tubes and sodium vapor lamps, when the sun set, light levels would drop, McNally said.

The brain would start to produce a hormone called melatonin, and other neurotransmitters would be activated, inducing sleep. When the sun rose, bright light would turn off melatonin production, and generally rig the brain for alert running.

Sitting in a brightly lit office is not the same. No matter how many lights are on, the sun is far more luminous. This could help explain the depth of morning grogginess.

Given early school starting times, too much work, an over abundance of entertainment, and glowing computer screens, the average person is sleep deprived, McNally said. People in the U.S. get about 6.5 to 7.5 hours of sleep a night, while 7.5 to 9 hours is necessary, he said.

Do not squander the extra hour, McNally advised. If you stay up an hour later, you haven’t pushed your sleep phase back at all. Then in March, when daylight saving starts anew, you lose an hour, and you’re in even more trouble.

“This is the time of year when you get a gift to reduce sleep phase delay. You sort of wish people would take that tack,” McNally said.