Thursday, April 5, 2012

Magnesium and Hypertension

When it comes to calcium and osteoporosis, everyone is agreed – NDs, MDs, acupuncturists, NPs, and chiropractors all recommend 1200 mg of calcium a day to help ward off the onset of osteoporosis. By contrast, there’s not as much discussion of magnesium when it comes to high blood pressure, despite an overwhelming amount of research into the topic, a fact at least partly explainable by inconsistent results in clinical studies. This week, I’m going to write on this topic, referencing select articles from the medical literature – there are thousands of articles on the topic of magnesium and hypertension, and it’s easy to get lost in the sea of literature.

Let me start by discussing briefly the epidemiological information on the topic. I won’t present studies here, though there are many, but in general, the research indicates that people who consume higher amounts of magnesium have, in general, a lower prevalence of hypertension, lower blood pressure in general, and lower incidence of stroke. Of course there are studies that have found no association, as is the case when you have enough studies devoted to a given topic, but a greater number of studies indicate that there is a relationship present, and the evidence is quite compelling.

One of the reasons that I’m inclined to believe the link is because there exist plausible mechanisms for magnesium’s ability to reduce blood pressure. A recent article published in the Journal of Clinical Hypertension elaborates on the biochemistry behind magnesium’s role in hypertension, indicating multiple pathways by which it acts to lower blood pressure, but primarily likening its action to that of a calcium channel blocker (a class of medication used for hypertension and chronic heart failure). Much like a calcium channel blocker, magnesium induces vasodilatation of arteries and regulates cardiac contractility, thus lowering blood pressure and improving the function of the heart. It’s also been suggested that the role that magnesium plays in reducing blood pressure is in part due to the action its presence exerts on other minerals in the body, including sodium, potassium and calcium.

As always, none of this should be taken without evidence that it actually lowers blood pressure in a clinical setting. A 2002 meta-analysis, which looked at 22 trials, including 1220 patients, found that magnesium provided mild benefit to hypertensive patients, although this benefit was dose-dependent, which suggests that greater benefit might be derived from higher doses of magnesium. Since then, further studies have been published that indicate benefit, albeit mild, from magnesium supplementation (1, 2). Taken together, these studies indicate that there is some benefit to be had from magnesium in regards to hypertension. However, all authors more or less agree that the benefit is somewhat inconsistent in clinical trials. The authors of the previously mentioned meta-analysis indicated that small studies and variable study design was a likely factor in the inconsistencies, and called for larger studies in order to more clearly define the benefit and role of magnesium in hypertension.

One piece of the puzzle that has as yet not been fully fleshed out, but which I believe is likely to answer many questions is that of magnesium deficiency. As early as 1983, a study published in the British Medical Journal showed that magnesium could reduce blood pressure significantly, and postulated that it was due to a correction of magnesium deficiency. However, this hasn’t been a major area of research in the intervening period, although a recent study showed that magnesium did produce surprisingly large decreases in blood pressure among a collection of hypertensive diabetics who also had low serum magnesium. This piece of information may give us clinical guidelines regarding when to prescribe magnesium for hypertension, and when to resort to other measures. There’s been some dispute in the past as to the best way to measure a patient’s magnesium status, but I think the clinical correlation here points the way forward.

So what’s the take home message? In all, magnesium does appear to provide some mild benefit in cases of hypertension, a benefit even more marked if the patient is demonstrably low in magnesium. As always, be in consultation with a healthcare provider about using nutritional supplements to help combat disease, especially one with consequences as serious as hypertension – additionally, magnesium is not without side effects, and it takes an experienced provider to help guide you through that.