3 questions about seasonal affective disorder — SAD — for the psychiatrist who discovered it

As much as there is to embrace about winter's approach for those who live in a place with changing seasons — holidays! cozy sweaters! snow! — there is also, for many people, a palpable dread. That's often due to the decrease in light and day length that can negatively affect one's mood, leading annually to seasonal affective disorder (SAD) in about 5% of the U.S. population.

SAD, first discovered and named in the 1980s by South African psychiatrist Dr. Norman Rosenthal, can cause symptoms from sadness to apathy, which can lead to troubles at work and in relationships and to deep depression, lasting an average of 40% of the year, until spring or summer comes back around.

For those who struggle with full-blown SAD — which is a subset of clinical depression and more severe than what some call the "winter blues" — there are plenty of treatments beyond waiting it out, from highly effective light therapy to medication and changes in diet.

Here, Rosenthal, a light-therapy pioneer and clinical professor of psychiatry at Georgetown University School of Medicine who has just released his 10th book, Defeating SAD: A Guide to Health and Happiness Through All Seasons, shares his insights.

1. How did you discover SAD?

"It was a process of some years," beginning when Rosenthal left Johannesburg for New York City to do his psychiatry residency at Columbia University, he tells Yahoo Life. "When I came, it was summertime, the days were long, and I really loved it. I had a lot of energy. And then winter came, and the days shortened and my energy declined." Because his home in South Africa sat about 27 degrees south of the equator and NYC is 40 degrees north, he points out, "I had never really been exposed to such a variability in the day length in all my life." But, he adds, "when spring came, I said, 'Well, that wasn't so bad,' and then I would pick everything up again. It would happen year after year, for three years."

Eventually, Rosenthal went to the National Institutes of Health and had to choose a topic of research. "We came across a man who had this kind of seasonal pattern, but much worse than me. I thought, 'Wow, there's really something here,'" he says.

Rosenthal put the elements of the syndrome together based on thousands of questionnaires and observed common symptoms, which he describes as "an increased need for sleep; difficulty waking up in the morning; an increased appetite, especially for sweets and starches; difficulty concentrating and focusing and getting your work done; and withdrawal." Then he and his team followed a cohort from the summer into the winter.

"They were just having the best time in the summer, just like I did that first summer, and one of my colleagues said, 'Well, what will you do if they don't get depressed on schedule? Won't you look foolish?' And I said, 'I think they're going to get depressed. And, you know, looking foolish is not the worst thing.' And sure enough," he recalls, "as the days got shorter, all the people who we'd been studying became depressed, one after the other, right on schedule. And we put them into a clinical trial. And then one of the most thrilling experiences in my research career, or even in my life, was seeing these people come out of their depression. We were all pretty much delighted, surprised, impressed, and realized that this was something real. We wrote it up, and that was our original paper in 1984."

His new book, he says, "is four decades in the making. It's a distillation of everything that I have learned that could be helpful to people."

2. How would you describe SAD?

In his book, Rosenthal defines the disorder as "a condition of regular depressions that occur in the fall and winter and typically remit in the spring and summer," mostly affecting women more than men and coming with variations, including some people who not only get depressed in winter but get "excessively exuberant" in summer. The way he describes it, though, is in our relation to both the animal kingdom and our productivity-focused society.

"If you look around the world, animals have seasonal rhythms in many instances — especially animals who evolved a little further from the equator, where there are seasonal rhythms of sunlight and day length," he says. "And while seasonal rhythms in nature can often be very adaptive and helpful — [as with] a hibernating bear — seasonal rhythms in humans can be a serious pain in the neck."

When someone has SAD, "the changes in behavior that predictably occur … starting when the days get shorter and continuing through the short days into the spring, can be manifold and problematic," prompting the symptoms that Rosenthal first observed in his study.

Further, he adds, "One of my early patients said, 'I should have been a bear. There's a lot to hibernate about' … and in that comment, she really pointed out that these seasonal rhythms, though widespread, are not well tolerated in the species that prides itself on functioning at a high level all year round. … There's very little tolerance for curling up with some munchies and waiting out the winter, you know? So that's the problem with seasonal affective disorder."

Rosenthal is often asked to explain the difference between depression and SAD. "That's as if you said, 'How is a cucumber different from a vegetable?' A cucumber is a type of vegetable. And in the family of depressions, SAD is one kind," he explains. "It could be just as bad — there has been the mistake of thinking that if it's SAD, it is mild, just because it's seasonal. But it's not necessarily so, and in fact, in my book, I talk about two people who were very suicidal. … But its pattern of occurrence tallies with the seasons. So that's what distinguishes it from nonseasonal depression."

3. What do we know about light therapy and other forms of SAD treatment?

Because SAD is tied to seasonal changes in light, Rosenthal's initial findings hypothesized that symptoms could be reversed by exposure to bright light. Since then, what's now known as bright light therapy or BLT — the use of SAD lamps, also called light boxes, available in a range of sizes and prices, at regular intervals — has been shown to be largely effective in over 60 studies.

"If you look at light therapy in the clinical trials, most people will respond, meaning that they are better on light therapy than off," he says, adding that a majority of people appear to need additional treatments in order to reach total remission. "Light therapy does the heavy lifting, but [there are] all these other things to get the best effect," he says, noting that if he sees a patient still having SAD symptoms even while sticking to a regimen of light therapy, he will make lifestyle-change suggestions. "I might say, 'Add exercise, and add exercise outside in the light. And what are you doing socially? Oh, you're hanging out at home. Make some arrangements. And have you booked any vacations to sunny places in the winter? Well, hurry up before the prices get high on the airfares.' So the sort of collective combination is much better than the light therapy alone."

He adds: "Light therapy is terrific. I don't want to talk it down. It's really been a major contribution not just to SAD but to depression in general, which is largely unknown. But it really works best if it's combined with other treatments. That's a central theme in the book. And that's why I have sections on foundational habits and medications, if you need them. And on CBT [cognitive behavioral therapy], which is an outstanding treatment."