These are the longest nights. From now until mid-January the sun will set before most of us are done with the day's work. We'll be coming home in darkness and leaving the house again before dawn. Some folks never see their home in daylight this time of year except on weekends.
This is a time of torpor, when many mammals take to their burrows for hibernation. Colder weather and shorter days signal biological changes in the Earth's creatures, including man. Holidays alone are not the reason we do more shopping, put on more weight and feel more tired than usual.
Each of us comes with a built-in biological clock that affects virtually every function of our bodies, including sleep. Blood pressure rises and falls, pulse quickens and slows, and glands secrete proteins according to daily -- or Circadian -- rhythms established by this inner timepiece.
Our inner clocks never need winding, but they must be reset -- daily. Otherwise, they run in 25-hour cycles. A body that woke at 5 a.m. Monday would expect to sleep until 6 a.m. Tuesday and 7 a.m. Wednesday. Likewise, our mealtime expectations would run an hour later each day until breakfasts would be taken in the evening and dinners at dawn.
Light signals from our environment, whether natural or artificial, set our inner clocks back to a 24-hour cycle. And when those signals say "winter," our bodies tend to want more sleep.
Not all creatures sleep the same, of course. Bears and squirrels and marmots hole up and drowse deeply almost the entire winter while birds and shrews only doze.
Among humans, there are short sleepers (less than 6 hours) and long sleepers (more than 9 hours) and a great many in between. All are affected by the winter season, but show it in different ways. Lethargy. Moodiness. Depression.
Some researchers have suggested that short sleepers tend to be more energetic, ambitious and successful. Because they have more waking hours to work with short sleepers can get more done. Others have theorized that the less sleep the shorter the lifespan.
"The only clear conclusion is that there is a rare subgroup of people who constitutionally need little sleep, many of whom appear to take advantage of the fact by getting more accomplished," reports Harvard Medical School psychiatry professor J. Allan Hobson in his book, "Sleep."
The world record short sleeper, he points out, is an Englishwoman who sleeps just 40 minutes a day. Doesn't she feel fortunate? Isn't she productive?
No, he adds, she's rather bored.
He probably caught her on a winter's day, or night more likely.
