April 24, 2006 — Nudging the body’s “clock,” or circadian rhythm, may help curb seasonal affective disorder (SAD), a new study shows.

SAD is a depression that occurs each year at the same time, usually starting in fall or winter and ending in spring or early summer. The exact cause of SAD isn’t known, but the amount of sunlight is an important factor.

The new study included 68 SAD patients. The goal was to see if the medication melatonin could adjust the patients’ internal clocks to cope with the later sunrise during winter.

The researchers included psychiatrist Alfred Lewy, MD, PhD, of Oregon Health & Science University.

“Although more studies are needed, these data suggest that most SAD patients might benefit from an appropriate low-dose formulation of melatonin taken in the afternoon,” they write.

The study appears in the online early edition of Proceedings of the National Academy of Sciences.

Shifting the Body Clock

Lewy’s team gave patients pills containing melatonin — a hormone triggered by darkness that helps govern the sleep/wake cycle — or a similar pill without melatonin (placebo). The body’s pineal gland makes melatonin; melatonin supplements are also widely available but aren’t subject to the same U.S. regulations as prescription drugs.

For three weeks during winter, the patients took a pill every two hours, starting when they woke up and ending four hours or two hours before sleep, for a total of seven or eight daily pills.

The patients were split into three groups. One group received melatonin in the morning and a placebo the rest of the day; another group got placebo in the morning and melatonin in the afternoon. The third group took placebo pills at all times. No one knew which pills contained melatonin.

The pill schedule and doses were based on the theory that “most SAD patients become depressed in the winter because of the later dawn,” the researchers write, calling melatonin “the chemical signal of darkness.”

Lewy and colleagues checked the patients’ depression severity before treatment and every week during the study.

Soothing SAD

The researchers found that in most patients SAD was linked to delayed sunrises. Those patients tended to respond best when they got melatonin in the afternoon. Afternoon melatonin shifted their body clock to earlier in the day.

SAD appeared to be linked to winter’s earlier sunsets in a smaller group of patients. Those patients responded best when they took melatonin in the morning.

The study shows that 17 patients received the “correct” treatment, meaning they got melatonin at the time of day that suited their condition best. In those patients, depression ratings decreased by 34%, compared with 13% to 15% for the other patients.

The study wasn’t intended to test melatonin as a SAD treatment. Further studies are needed for that, write Lewy and colleagues.

They add that their findings could also prompt new studies on nonseasonal depression, as well as other sleep problems and psychiatric disorders that might involve circadian rhythms.

The journal states that Lewy is a co-inventor on several melatonin-use patents owned by Oregon Health & Science University, currently not licensed to any company.