The Winter Side Of Our Humanity Change Of Seasons Brings On Many Changes In Our Bodies

Light is the signature that winter scrawls across the sky, writ low over the horizon in muted shades and cursive script.

Buildings cast elongated shadows, condemning to darkness sidewalks and streets. Light illuminates rooftops and punches through at alleys and side roads. But when we turn, instinctively, toward that warmth, we may instead be blasted by icy wind. Stung by dark and discomfort, we retreat indoors where artificial light creates an endless summer.

Winter is not defined by short days and long nights alone. In fact, winter’s onset begins a march toward spring that typically offers an extra minute or so of sunshine each day.

But recently, there has been an effort to strip sunlight of myth and subject it to science. Human response to the seasonal cycles of daylight, once disdained as fringe research, is burgeoning into a fertile field. Neuroscientists now know the brain retains vestiges of a past in which the season was master.

“We are much more biological creatures than we have admitted to ourselves, and I think part of that is our desire and need for light in our lives,” said Judith Heerwagen, senior research scientist at Battelle, a Seattle research center.

“We didn’t evolve in caves or in buildings,” said Heerwagen, a psychologist who studies the effect of windows and lighting on productivity. “A lot of our biorhythms, our emotional centers, are really tied to biological processes and contact with nature and natural things. This, particularly, is manifested in the winter when we spend more time indoors.”

Light is, in a sense, the key that winds our internal clocks, sets our daily and seasonal rhythms and, perhaps, influences mood.

Fred Turek, who studies seasonal and circadian rhythms in mammals at his laboratory at Northwestern University in Evanston, Ill., puts it another way: “Light is central.”

A hormone, melatonin, produced by the pineal gland inside the brain lets humans and other animals recognize changes in the length of the day. Melatonin is the chemical companion of the night, secreted primarily when it is dark. Because nights are longer in winter than in summer, melatonin serves as a seasonal signal.

“In ways that we don’t understand, the duration of melatonin signals other areas of the brain that the day is long or the day is short,” said Turek, chairman of the department of neurobiology and physiology at Northwestern.

Scientists now are studying precisely how melatonin orchestrates a body’s daily, or circadian, rhythms and how that controls seasonal changes in physiology and behavior.

Human winter and summer selves may not be as distinct as those experienced by Siberian hamsters. But the more scientists began to look for human response to seasonal change, the more evidence they found. Consider the fall feeding instinct.

A number of animal species prepare for winter by gorging on food during fall, the traditional season of harvest. In recent studies of human eating behavior, psychologist John de Castro found that people do the same thing.

Beginning in October and continuing for about three months, people consume an average of about 220 extra calories per day, adding about 5.5 pounds over the season. Not only are they eating more food, they’re eating different kinds: more carbohydrates, fat and sugar.

Put another way, we act like chipmunks bracing for winter by fattening up in fall.

“Most people are quite surprised by this. They figure they’re eating more because of the holidays. But these data are exclusive of the holidays,” said de Castro, a professor of psychology at Georgia State University who studies eating.

How do people “know” to do this?

“There’s no way of telling what it is in humans, but in animal species it’s the light, the length of the day, that sets these things off,” de Castro said.

At the University of Massachusetts Medical Center, Dr. Ira Ockene also has detected the blush of winter light on human lives.

He found it in blood.

When screening people for a study on cholesterol, Ockene found that the levels in winter averaged 20 points higher than those in summer.

“Which is the right one?” asked Ockene, a cardiologist. “I haven’t a clue. Should people only have their cholesterol tested in the winter because it’s at its highest? We don’t know the answers to those questions at all, but they have huge implications.”

Equally puzzling to Ockene is the fact that some doctors have known of this variation at least since the 1930s, and “no one has ever made anything of it.” Case in point: A recent set of cholesterol guidelines given to physicians by the National Institutes of Health never mentions the word season.

Doctors also know that levels of fibrinogen, one of blood’s major clotting factors, is higher in winter, and that the incidence of heart attack deaths is greater as well.

Intrigued about the relationships, Ockene is in the midst of a federally funded study to chart cholesterol’s seasonal cycle. He is looking at the cholesterol levels of 600 people five times during a year and coupling those readings with weather data. His research team includes a meteorologist, an exercise physiologist and a psychologist.

Winter sends us into a literal retreat. Downtown plazas that teem with urban vibrancy in other seasons may be devoid of even pigeons during cold weather. Some people withdraw emotionally as well, displaying distinct summer and winter personalities. A kind of a depression typically begins its onset in late fall and is worst in January and February. The diagnosis: Seasonal Affective Disorder.

The incidence of the disorder, with the apt acronym SAD, is very low in Florida, but rises to about 10 percent in the far northern United States. Symptoms include a blue mood, craving for junk food, weight gain of as much as 30 pounds and an overwhelming desire to sleep two or three extra hours each night.