Melatonin's role in protecting the heart – the evidence so far

Many people know of melatonin as the sleep hormone – and, indeed, that’s what most of the research on melatonin has focused on. However, melatonin is also an antioxidant, protecting cells from harmful “free radicals” that can damage DNA – and this includes protecting cells in the heart and blood vessels.

Given that heart disease is the leading cause of death in the world, killing around 17.9 million people each year, this action is of particular interest to researchers.

Research shows that people with cardiovascular disease have lower levels of melatonin in their blood compared with healthy people. And there is a strong inverse relationship between melatonin levels and cardiovascular disease. In other words, the lower a person’s melatonin level, the higher their risk of cardiovascular disease.

Melatonin supplements (2.5mg taken one hour before sleep) have been shown to reduce blood pressure. And, of course, high blood pressure (hypertension) is a known risk factor for cardiovascular disease. Also, so-called cardiovascular events, including heart attacks and sudden cardiac death (unexpected death caused by a change in heart rhythm), occur at a higher rate in the early morning when melatonin is at its lowest. These studies strongly suggest that melatonin protects the heart and blood vessels.

Importantly, patients who have had a heart attack have reduced nighttime melatonin levels. This observation has led to the theory that melatonin may be able to improve recovery from a heart attack and form part of the standard treatment given immediately after a heart attack occurs.

Laboratory studies of heart attack (using rats’ hearts kept alive outside of their bodies) have shown that melatonin does indeed protect the heart from damage after a heart attack. Similar studies have shown that when rats’ hearts are deprived of oxygen, as occurs in a heart attack, providing the heart with melatonin had a protective effect.

Evidence less certain in people

In humans, the evidence is less clear. A large trial where melatonin was injected into patients’ hearts after a heart attack showed no beneficial effects. A later analysis of the same data suggested that melatonin reduced the size of damage caused to the heart by being starved of oxygen during a heart attack. And a similar clinical trial suggested no beneficial effects of giving melatonin to people who had suffered a heart attack. So the evidence is contradictory and no clear picture of melatonin’s role in helping to prevent damage to the heart during a heart attack has emerged so far.

It has been suggested that giving melatonin orally after a heart attack, rather than directly to the heart, could explain the contradictory findings in clinical trials.

Trials looking at the effect of melatonin on heart attack are still in the relatively early stages, and it is clear further studies are needed to look at how and when melatonin could be administered after a heart attack.

However, it is clear that melatonin levels decline as we get older, and this may lead to an increased risk of heart disease.

As melatonin pills are only available on prescription in the UK, EU and Australia, melatonin levels can’t be topped up with a supplement – as can be done with other hormones, such as vitamin D. Ultimately, eating a diet that contains foods rich in melatonin, such as milk, eggs, grapes, walnuts and grains, may help protect you from cardiovascular disease. Melatonin is also found in wine, and some suggest that this may explain red wine’s heart-protective effects.

James Brown does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.