As a nutrition support pharmacist, you will get more questions about magnesium supplements, it is the top-selling supplement that’s often touted as “the miracle mineral”. Magnesium plays a key role in processes from bone development, to blood pressure regulation, to muscle and nerve function. We know to use magnesium for hypomagnesemia, such as due to GI losses (celiac disease, Crohn’s, etc) or medications (diuretics, PPIs, etc).
And magnesium is an old standby for constipation or heartburn. But don’t suggest oral magnesium supplements for energy, insomnia or leg cramps. There’s not good evidence for these uses. Also don’t turn to magnesium supplements for high blood pressure. Weak evidence suggests blood pressure lowering of only about 2 mmHg. Use these tips when choosing a mag supplement, if appropriate.
Magnesium oxide (Mag-Ox, etc) doesn’t seem to be as well absorbed as other forms, including magnesium chloride, magnesium citrate (Cal-Mag), magnesium glycinate or mag lactate. But any of these forms can be used to replete low levels and magnesium oxide is often the least costly. Advise patients to check labels for elemental magnesium content, about 300 to 400 mg/day is the recommended intake for most adults. But consider higher doses (800 mg BID, etc) for a day or so to replete low levels. Dietary magnesium (greens, nuts, whole grains, etc) is a good way for most patients to meet their daily needs. For example, there’s about 75 mg of magnesium in a half cup of cooked spinach. But a supplement is usually needed to replete low levels.
If practical, divide the dose to improve absorption, and possibly reduce GI upset (diarrhea, nausea, etc). Keep in mind, it’s not necessary to check magnesium levels if patients are just trying a supplement. But monitor if you’re repleting magnesium or in patients with severe kidney disease.
References
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National Institutes of Health (2016). Office of Dietary Supplements - Magnesium. [online] Nih.gov. Available at: https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional
Schuchardt JP, Hahn A. Intestinal Absorption and Factors Influencing Bioavailability of Magnesium-An Update. Curr Nutr Food Sci. 2017 Nov;13(4):260-278. Available at: http://www.eurekaselect.com/article/83107, Or https://pubmed.ncbi.nlm.nih.gov/29123461
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