Many people take a daily magnesium supplement. But does it help lower your blood pressure? The official view that doctors are advised to take is that we shouldn’t recommend magnesium supplements to lower blood pressure. But what is this based upon? And in that case, why do many people take it anyway?
What research has been done?
The main problem is that the studies that have been done to look at the effect of magnesium supplements on blood pressure have often not been well designed. The best studies are called randomised controlled trials. That means that people are randomly assigned to take either magnesium or a placebo pill. This is essential to try to detect any benefit from magnesium or any other medication. The placebo effect is so powerful that unless you control for it in this way, it’s impossible to know if you are measuring benefit from the magnesium or just from giving someone any old pill.
The good news is that there are a number of studies that have looked at the benefit of magnesium on high blood pressure which were designed as randomised controlled trials. The bad news is that when this was last reviewed a few years ago, the total number of patients in all of those studies was small (about 500). This may not be enough to detect the effects reliably. The second bit of bad news is that most of those studies still had significant potential flaws. This included things like whether the group of people who received the magnesium or the placebo pill were similar to start with so that they could be compared to one another.
What did the research show?
Taking all that into account, what did the small number of patients in these studies show when they took a daily magnesium supplement? The doses taken varied between 10mmol to 40mmol a day and there was no difference in benefit seen depending on dose. Averaging out the effect across all the studies showed no change to the systolic blood pressure BUT it did show a drop in the diastolic blood pressure. The other bit of good news is that the number of people who decided to stop the pills was the same in the placebo and the magnesium groups so no significant side effects were detected.
And so this is probably why some people, quite reasonably, take magnesium supplements. We don’t know for sure if it does help, but there doesn’t appear to be any harm and there might be some benefit. But as doctors, we haven’t got enough reliable information to be able to give a recommendation.