In a study conducted by Dr. Cagnacci at the Institute of Obstetrics and Gynecology, University of Cagliari in Italy, twelve young women were given one mg of melatonin during the day and then had their heart rate and blood pressure measured. These cardiovascular parameters were also measured on another day when the women were given placebo pills. In comparison to the placebo, the administration of melatonin reduced, within 90 minutes, systolic and diastolic blood pressure, along with heart rate.

Cagnacci A, Arangino S, Angiolucci M, et al. Potentially beneficial cardiovascular effects of melatonin administration in women. J Pineal Research 22:16-19, 1997.

Comments: It would be interesting to do a study evaluating heart rate, blood pressure, breathing rate and temperature throughout the night when administering a small, physiological dose of melatonin. If we do find that melatonin is able to lower heart rate and blood pressure throughout the night, this would be a very positive finding indicating that the use of melatonin could potentially provide long-term benefits to the cardiovascular system. However, long-term studies would be indicated to see whether there is a tolerance to the melatonin after a few weeks.

In the meantime, I still feel that the use of melatonin once, twice or three times a week is safe, especially when taken in amounts less than one mg. I know many people who were influence by the hype on melatonin two years ago and started taking nightly doses of 3, 6, or even 9 mg. I don't think this is a wise decision based on the limited information we have on the long-term use of this hormone. However, I'm comfortable enough about the safety of melatonin that I'm continuing using it. For the past three years, I have taken between 0.2 and 1 mg about twice a week without any side effects.