Looking for the causes of summertime blues

The causes of summertime depression are not well understood.

But then, the condition was identified only recently and remains an understudied area of research. Winter depression was first described in a 1984 study, and the summer form of seasonal depression was described in a 1987 study. Seasonal patterns of depression were officially recognized in the Diagnostic and Statistical Manual of Mental Disorders in 1987.

“Summer seasonal affective disorder is the same major depressive disorder that any psychiatrist would call a major depression, with the additional criteria that it specifically occurs in the summer months and resolves during the winter months each year,” says Dr. Dan Oren, an adjunct associate professor of psychiatry at Yale University who has studied seasonal disorders.

The winter version is widely believed to be associated with the shortened days and decreased exposure to sunlight; in summer depression, some researchers believe that heat and humidity may play a more significant role than length of day.


However, Dr. Alfred Lewy, a professor of psychiatry at Oregon Health and Science University, who has studied seasonal disorders for 30 years, says it is possible that there are two distinct types of summer depression: one linked to the light-dark cycle and another that relates to temperature and humidity.

But, he adds, because researchers are still learning so much about these conditions, “five years from now there may be only one type of summer depression — the one linked to day length. But we don’t know that yet.”

Dr. Norman Rosenthal, a clinical professor of psychiatry at Georgetown University Medical School who has studied seasonal disorders, suggests that the intensity of sunlight may play a role in seasonal depression. “One of my patients talks about how she feels the bright sunlight cutting through her like a knife,” he says.

Listless summers

Ellen Frank, a professor of psychiatry and psychology at the University of Pittsburgh School of Medicine, has been studying mood disorders for the last 30 years. Frank herself has suffered with summer depression, which she began to recognize when she was around 12 years old.

“I always felt kind of yucky and listless in the summer and full of energy in the winter,” says Frank. “Going back to my even pre-adolescence, I can remember lying on my bed in the summer, unmotivated to go out and do anything.”

She also had trouble with her weight during the summer but easily shed pounds in the winter. Later on, in her professional life, Frank recalls how her productivity would be diminished during the summer months.

“We had major grant application deadlines or grant site visits … and I would just find myself barely functional,” says Frank. But around 9:45 in the evening — when it gets dark in the summertime on much of the East Coast — she would get a surge of energy. “All of the things that I couldn’t do during the day were possible.”


Then, 20 years ago, she met Dr. David Avery, a psychiatrist at the University of Washington in Seattle. After she explained her summer symptoms, she recalls, Avery suggested a possible antidote: He told her to wake early in the morning, at sunrise, and expose herself to sunlight for a few minutes when the sun first begins to peak over the horizon. “And I was cured,” says Frank.

Frank still uses this technique to manage her summer depression. As early as 5:45 a.m., when the sun rises on parts of the East Coast, “I stand on the street and look toward the horizon where I know the sun comes up, and it seems to be really important, for me anyhow, to actually see the sun,” says Frank.

If the sun is blocked by trees or buildings, she walks down the street until she has a clear view and remains for a few minutes. “Then I come in and start my day.” Frank no longer suffers with her summer depression. But if she misses a few days of her morning light routine, Frank feels her symptoms returning.

Mistimed clocks


Lewy believes that his theory, known as the “phase shift hypothesis,” could explain symptoms such as Frank’s — and her cure.

For the last 30 years, Lewy has been investigating whether some people who suffer winter depressions have what he calls circadian “misalignments,” in which a person’s day and night cycles fall out of sync. “As dawn is later in the winter, your circadian rhythms drift later with the later dawn and drift out of phase with the sleep-wake cycle, so there’s a misalignment,” says Lewy. “Kind of like having jet lag, although for five months.”

Lewy’s work suggests that light therapy at the correct time of day can reset a person’s daily clock. Light has an antidepressant effect because it resets the body clock in the correct direction, says Lewy.

In 1987, Lewy published a study suggesting that morning light shifts the body clock earlier and that evening light shifts the body clock later. In a 2006 study, Lewy established that a mistimed body clock plays an important role in winter depression.


A 2009 study in Psychiatry Research concludes that this “circadian misalignment” could also be the underlying factor in nonseasonal depression.