"It has been reported that people with high blood pressure often have suppressed nighttime melatonin levels," Scheer said. "We have recently found that people with high blood pressure have actual anatomical disturbances of their biological clocks. This finding might open the door for a new approach for treating hypertension."
Scheer and colleagues conducted the study at the Netherlands Institute for Brain Research in Amsterdam. They evaluated melatonin's effect after a single dose versus after a longer regimen. For three weeks, researchers gave 16 men with untreated essential hypertension (high blood pressure with no known cause) either placebo or 2.5 mg oral melatonin one hour before they went to sleep. They compared the effect of the three-week course to taking melatonin only on one day.
The researchers found that patients taking repeated melatonin had lower nighttime systolic blood pressure (the top number in a blood pressure reading) by 6 millimeters of mercury (mm Hg) and diastolic blood pressure (bottom number) by 4 mm Hg. The single dose of melatonin had no effect on blood pressure. Patients taking melatonin also reported improved sleep, but Scheer said that effect was unrelated to blood pressure reduction in this study.
While this small study suggests the biological clock might be a mechanism involved in the blood pressure reduction, Scheer and colleagues don't exclude that improved sleep over a long time might help reduce blood pressure as well.
Dan Jones, M.D., an American Heart Association spokesperson and high blood pressure expert, added a word of caution about the study findings: "This report showing a blood pressure-lowering effect of melatonin use is of interest primarily at a theoretical or research level. Larger studies certainly would be needed prior to recommending this approach to patients with high blood pressure."
"Patients with high blood pressure should consult their own health care provider for specific advice, but no one should begin melatonin therapy for blood pressure management for the time being," added Jones, who is dean of the University of Mississippi Medical Center School of Medicine in Jackson, Miss.
Scheer agreed. "This is just a start. Large-scale studies need to be done, as well as studies of potential interactions between melatonin and traditional antihypertensive treatments."
Co-authors are Gert A. Van Montfrans, Eus J.W. van Someren, Gideon Mairuhu and Ruud M. Buijs.
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