Prolonged melatonin administration decreases nocturnal blood pressure in women.
BACKGROUND
The nocturnal decline of blood pressure (BP) is almost coincident with the elevation of melatonin, which may exert vasodilatating and hypotensive effects. In this study we investigated whether prolonged nocturnal administration of melatonin could influence the daily rhythm of BP in women.


METHODS
In a randomized double-blind study, 18 women, 47 to 63 years of age and with normal BP (N = 9) or treated essential hypertension (N = 9), received a 3-week course of a slow-release melatonin pill (3 mg) or placebo 1 h before going to bed. They were then crossed over to the other treatment for another 3 weeks. In each woman ambulatory BP was recorded for 41 h at baseline at the end of each treatment period.


RESULTS
In comparison with placebo, melatonin administration did not influence diurnal BP but did significantly decrease nocturnal systolic (-3.77 +/- 1.7 mm Hg, P = .0423), diastolic (-3.63 +/- 1.3 mm Hg, P = .0153), and mean (-3.71 +/- 1.3 mm Hg, P = .013) BP without modifying heart rate. The effect was inversely related to the day-night difference in BP.


CONCLUSION
These data indicate that prolonged administration of melatonin may improve the day-night rhythm of BP, particularly in women with a blunted nocturnal decline.