Melatonin is a sleep hormone, produced by the pineal gland seated deep inside the brain, as well as other parts of the body, such as the gastrointestinal tract. For years, melatonin has been recognized as a regulator of circadian rhythms, the natural cycle of sleep and wakefulness that has allowed humans to inhabit the earth in phase with the cycles of night and day.

Exposure of the retina (in the back of the eye) to light suppresses release of melatonin into the blood; darkness triggers release. Nighttime levels of melatonin surge 10-fold higher compared to that of daytime levels. In the modern world, authorities have proposed that lack of melatonin may be a by-product of interior lighting that extends into the evening hours. Evidence has emerged suggesting that lack of melatonin may contribute to increased potential for heart disease.

Supplementation of this fascinating hormone has shown potential benefit through a variety of favorable effects on cardiovascular parameters, including anti-oxidative action on LDL cholesterol, reduction in sympathetic (adrenaline-driven) tone, and reduction in blood pressure (BP).

Several studies document the blood pressure-reducing effect of melatonin:

Daily nighttime melatonin reduces blood pressure in male patients with essential hypertension. Once-nightly melatonin, 2.5 mg, reduced nighttime and daytime blood pressures in male subjects.

Melatonin reduces night blood pressure in patients with nocturnal hypertension. Because hypertension that persists during sleep has been suspected to be related to inadequate melatonin release, this study documents that melatonin supplementation, 2 mg sustained-release, reduces nighttime BP in the population with this condition.

Prolonged melatonin administration decreases nocturnal blood pressure in women.
The BP-reducing effect of melatonin, 3 mg sustained-release, extends to women with diabetes.

(But blood pressure may be increased when melatonin is added to nifedipine, a calcium channel blocker: Cardiovascular effects of melatonin in hypertensive patients well controlled by nifedipine: a 24-hour study.)

Effects on BP tend to be modest, on the order of 5-8 mmHg reduction in systolic, half that in diastolic.

But don't pooh-pooh such small reductions, as small reductions exert several-fold larger reductions in cardiovascular events like heart attack and stroke. The National Institutes of Health-sponsored NHANES data (see JNC VII), for example, document a doubling of risk for each increment of BP of 20/10. The Camelot Study demonstrated a reduction in cardiovascular events from 23% in placebo subjects to 16.7% in subjects taking amlodipine (Norvasc) with a 5 mm reduction in systolic pressure, 2 mmHg drop in diastolic pressure. Small changes, but big benefits.

Many people take melatonin at bedtime and are disappointed with the sleep-promoting effects. However, a much better way is to take melatonin several hours before bedtime, e.g., take at 7 pm to fall asleep at 10 pm. Don't think of melatonin as a sleeping pill; think of it as a sleep hormone, something that simply prepares your body for sleep by slowing heart rate, reducing body temperature, and reducing blood pressure. (You may need to modify the interval between taking melatonin and sleep, since individual responsiveness varies quite a bit.)