In the News

Scientists are joining poets and artists in celebrating light.

Light, it turns out, is good for the body as well as the soul, they say. Scientists being scientists, however, they also can't help but throw in a caveat or two.

Take, for instance, people who suffer from seasonal affective disorder. For most people, springtime and its increased amount of daylight marks the seasonal end of the debilitating depression that marks the illness.

However, for a few people with bipolar disorder, the increased levels of light work a little too well.

"They can become overly activated, fully manic or what we call hypo-manic," says Dr. Andrew Winokur, professor of psychiatry and director of psychopharmacology at the University of Connecticut Health Center.

These people are more likely to engage in risky and inappropriate behavior as mania replaces depression.

"It is a dangerous condition," agrees Dr. Michael Terman, director of the clinical chronobiology program at Columbia University Medical Center.

Terman notes that suicide rates peak during spring in northern latitudes. One theory is that the increased exposure to daylight triggers changes in brain chemistry in depressed people that allow them to act on harmful thoughts.

Seasonal affective disorder "is marked by a tremendous lethargy," he says. "But then comes a transition period in the spring when there is an energy boost, and people become more likely to act on suicidal thoughts."

These harmful effects of light, however, are the exceptions to a fundamental and often overlooked point, Terman says: "We are designed to be in the sun."

Chronobiology is a relatively new science that tracks the effects of circadian rhythms, or the body's internal clock, on health and behavior.

In almost all species, it is sunlight that sets the internal clock, which governs functions such as sleep and wakefulness. Malfunctions of the internal clock have been implicated in several neurological, cardiovascular and hormonal disorders.

And it is sunlight that helps time the release of melatonin, which signals the onset of sleep and appears to regulate the release of a wide variety of other hormones in regulating biological rhythms.

Most people experience the effects of disrupted circadian rhythms only when they suffer jet lag, a consequence of traveling across several time zones.

However, Winokur estimates that one in four people experience some form of seasonal mood change in which they feel at least slightly more vibrant in the spring and slightly more depressed in winter.

By studying people who become sick from the absence of light, Terman has developed ideas about why light helps provide an emotional lift for people.

When prescribing light therapy for patients with the disorder, the intensity of the light and the duration for which patients are exposed are important factors, he says. However, the most critical element in effective treatment is the time of day patients are exposed to light.

The most beneficial time for light is about 8.5 hours after melatonin levels rise, signaling the onset of sleep, Terman says. But he notes that optimum levels of melatonin can vary six hours between larks, or morning people, and owls, or night people.

Winokur says that's why he often advises depressed patients to get up and take a walk in early-morning light, which tends to have an energizing effect.

Other researchers have noted that certain elements of light may be more beneficial than others.

Mark Rea, director of lighting research at Rensselaer Polytechnic Institute, has studied the optimum lighting conditions for people working overnight. It turns out that nurses and other night-shift workers report feeling more alert when they are exposed to the blue spectrum of light -- the same spectrum of light we find on cloudless days.

The lesson is that we should make sure we get enough natural light every day, they say.

"As our modern society developed, we have tremendously restricted the outdoor levels of light we get," Terman says. "Even in San Diego, a healthy young male gets an average of 20 minutes of light exposure a day. We live with a sort of self-imposed light deprivation."