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MONDAY, Jan. 19 (HealthDayNews) -- Melatonin may do more than cure jet lag.

Researchers have found taking supplements of the hormone at night helped reduce blood pressure levels in a small number of men.

Pending further investigation, this over-the-counter supplement could join the arsenal of effective blood pressure treatments, the authors of a new study say.

Researchers have learned recently that people suffering from high blood pressure have disturbances in their biological clocks, which are tied to light and dark and regulate sleep patterns. Exactly how the two are linked is not yet known.

"There is an early morning peak in cardiovascular incidents [heart attacks]," says Frank A.J.L. Scheer, lead author of the study appearing in the February issue of Hypertension.

"Since in the early morning there are also changes induced by the circadian rhythm [biological clock], a hypothesis was that disturbances of this circadian rhythm might be one of the underlying mechanisms of this increased peak in the early morning. And that by restoring the anticipatory functionality of the biological clock [with melatonin], we might be able to counteract that," Scheer adds.

Scheer is a neuroscientist at Brigham and Women's Hospital and Harvard Medical School Division of Sleep Medicine, both in Boston.

Others caution it's too early to draw any firm conclusions about melatonin's ability to control blood pressure.

"It's obviously a wait-and-see situation," says Dr. Michael Schloss, co-director of the New York University Lipid Treatment and Research Center and a clinical associate professor of medicine at NYU School of Medicine.

Melatonin is a hormone produced by the body's pineal gland. As darkness arrives, the pineal gland kicks into action. As melatonin production rises, people start to feel less alert and sleepy. Melatonin levels decline with sunrise, and remain low throughout the day.

Scheer and his colleagues looked at 16 men, all of whom had untreated high blood pressure, at the Netherlands Institute for Brain Research in Amsterdam. The men were randomly assigned to receive either a placebo, a single dose of melatonin or 2.5 milligrams of melatonin one hour before bedtime for three weeks. The study was designed so all the men would be assigned to each group at one point.

While the men taking the placebo or the single dose of melatonin experienced no change in their blood pressure, those taking the hormone each night throughout the three weeks had lower nighttime systolic and diastolic blood pressure. Systolic blood pressure (the top number in the reading) decreased by an average of six millimeters of mercury while the diastolic blood pressure (the bottom number) decreased by an average of four millimeters of mercury.

Participants taking melatonin also reported sleeping better, but this was not necessarily related to changes in their blood pressure.

"We did not find such a correlation in this study," Scheer says. "We, however, don't exclude that chronically improved sleep may also contribute to the lower blood pressure. The improvement of sleep by repeated and not by single melatonin actually further supports the hypothesis of the increase in the circadian rhythm output of the biological clock."

No one is sure why these changes took place, only that they are potentially significant. People are asleep for about a third of their lives, the study authors point out, and nighttime blood pressure seems to be a better predictor of cardiovascular risk than daytime blood pressure. Melatonin may be effective in reducing morning blood pressure, which may be contributing to the increased risk at that time, the study authors say.

Still, experts, including the study authors, caution patients not to do anything just yet.

"From a medical point of view, more patients need to be studied," Scheer says. "Also, in our study the patients were untreated by any other medication and because many people with hypertension are treated already by regular hypertensive drugs, it also would need to be established how co-treatments would affect the blood pressure."

More information

The National Sleep Foundation has more on melatonin. The American Heart Association has more on blood pressure.

(SOURCES: Frank A.J.L. Scheer, Ph.D., neuroscientist, Brigham and Women's Hospital, and Harvard Medical School Division of Sleep Medicine, both in Boston; Michael Schloss, M.D., co-director, New York University Lipid Treatment and Research Center, and clinical associate professor, medicine, New York University School of Medicine, New York City; February 2004 Hypertension)

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