63 senior respondents of a mean age of 80 were studied during 3 consecutive weeks. First week control data were collected for 7 successive days. Over the next 2 weeks, the seniors were administered a low dose of melatonin (1.5 mg) each day by night at 10:30 p.m. On the third week data were monitored again.
Melatonin significantly reduced BP. The hypotensive effect was dependent on time. The maximum systolic BP lowering effect of melatonin falls between 3:00 and 8:00 in the morning, the time of the highest risk of heart attacks and strokes. Nighttime and morning BP decreased more profoundly on average -8/3.5 mm Hg for SBP/DBP, respectively.
Moreover, the higher the mean systolic BP was during the first week, the more it dropped on the second week of melatonin administration. Melatonin also decreased the overall variability in BP.
Melatonin ws effective in synchronizing disrupted circadian rhythms of BP, heart rate and body temperature, making these circadian rhythms smoother and less irregular. None of these effects was found in 34 placebo treated seniors, thus ruling out the possibility that rhythms could be improved just because of regular schedule and presence of medical personal who took measurements.