That Internal Clock Runs a Touch Slow
Writing in the journal Science, researchers at Harvard Medical School who looked at subjects of varying ages found the circadian period (occurring approximately every 24 hours) of healthy adults averages 24 hours, 11 minutes instead of 25 hours as previously believed. And the human "day" changes little with age.
The researchers found that while older individuals tend to awaken earlier, it may be due to a higher exposure or sensitivity to light, not a change in the "circadian pacemaker."
Despite the early awakenings, a spokesman for the National Institute on Aging says the Harvard study "indicates that changes in the circadian clock are not inevitable with age but sleep-wake cycles among mature adults may be affected by their sleep phase peaking earlier.