Melatonin supplements are currently taken in the US to reduce the effects of jet lag. But this ability to help regulate the body's biological clock may be linked to melatonin's effect on blood pressure, says Dr Frank A.J.L. Scheer, a neuroscientist at Brigham and Women's Hospital and at Harvard Medical School's division of sleep medicine.
"It has been reported that people with high blood pressure often have suppressed night-time melatonin levels. 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," he said.
In a study conducted at the Netherlands Institute for Brain Research in Amsterdam, Scheer and colleagues 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 2.5mg 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 night-time 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 do not exclude that improved sleep over a long time might help reduce blood pressure as well.
Scheer added: "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."
Last year UK scientists from the Cochrane Collaboration called for funding to back proper testing of melatonin in supplement form so that it can be widely used by the public. There are currently no purity standards for the supplement, or enough clinical evidence to support its safety, despite the fact that it is very popular in many countries, they said.
A recent study suggested that melatonin supplements may worsen symptoms for asthma patients.