Dispelling nutrition myths, ranting, and occasionally, raving

What you need to know about magnesium

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Photo “nuts!” by Adam Wyles on Flickr, used under a Creative Commons Licence.

I recently read an article about magnesium that someone shared on facebook. Shockingly, for FB, it wasn’t nearly as inaccurate as I had expected. However, there were a couple of things in it that I wanted to address. The premise of the article was that most of us are magnesium deficient. This is untrue. Most of us don’t consume enough magnesium but there’s a world of difference between that, and being truly deficient. Magnesium deficiency manifests as an irregular heartbeat which may be accompanied by weakness, muscle spasms, disorientation, nausea, vomiting, and seizures. People who are at greatest risk of magnesium deficiency include: users of some diuretics, those with diabetes, people with alcoholism, as well as those who live in climates where they experience frequent heavy perspiration or those who have long bouts of vomiting or diarrhea.

So, how much magnesium should you be consuming? If you’re a man between 19 and 30 years of age, you should be consuming about 400 mg a day. Women in this age group should be consuming about 310 mg a day. Needs increase beyond this age by about 20 mg/d for men and 10 mg/d for women, and for those experiencing the conditions listed above. For more information of magnesium recommendations, click here. According to one of my old nutrition textbooks (Perspectives in Nutrition by Wardlaw and Hampl), assuming things haven’t changed that much in the past eight years, men consume 325 mg, women 225 mg, on average each day.

It’s not that terribly difficult to reach the recommended intakes of magnesium. One cup of spinach contains 157 mg, one cup of squash `105 mg, 1/4 cup of wheat germ 90 mg, 1/2 cup of navy beans 54 mg, 1 cup of plain yoghurt 43 mg… Nuts and seeds are also good sources of magnesium; as is dark chocolate and raw cacao (nibs, powder). Other leafy greens, beans, and legumes are also good sources of magnesium.

If you do decide to take a magnesium supplement, you should be aware that they are not all the same. Magnesium oxide tends to be the most common and inexpensive form of supplemental magnesium. However, it is also the most poorly absorbed form of magnesium. Liquid magnesium supplements will be best absorbed; the quantity of magnesium listed on the label is not as important as the form. As far as tablets and capsules go, Magnesium lactate, magnesium gluconate, and magnesium citrate are the most absorbable. However, magnesium citrate may have laxative effects, and magnesium hydroxide and magnesium sulfate are forms commonly used as laxatives. Zinc supplementation may interfere with magnesium absorption, while vitamin D supplementation may enhance magnesium absorption. Some medications may also affect magnesium absorption. As with any supplement, you should always check with your pharmacist to ensure that there will be no interactions with any other medications you’re taking. As with any nutrient, it’s best to try to get it from your food rather than from a supplement.

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Author: Diana

I'm a registered dietitian from Nova Scotia, living and working in Ontario, Canada. My goal is to help people relearn how to have a healthy relationship with food.

6 thoughts on “What you need to know about magnesium

  1. Enjoyed the article. I had restless leg syndrome. When I was on mirapex I had the side effect of unsual gambling behavior (don’t even like to play nickle buck with the family – nickle buck is a card game). Because of the mild side effect the neurologist and I decide to discontinue the medication. Then she perscribed magnesium, D3 and calcium – no more restless legs unless I am having a very stressful day

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    • Interesting. Thanks for sharing your experience Shirley! I think we too often overlook vitamin and mineral supplements as medications and turn to prescription drugs as the first method of treatment.

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  2. Interesting post. Good advice about consulting your pharmacist to try to avoid negative interactions if you are taking other supplements or prescription medications. Don’t stop there. Read the information sheets for your prescriptions carefully. Back around 1998 I was “diagnosed” with adult onset asthma, and started using puffers for relief. A few years ago I had a really bad asthma attack. I also have glaucoma, and use eye drops to keep the pressure at a reasonable level. Then one day I was reading the information sheet for one of the drops I was taking and noticed that it said that the drops could cause or aggravate asthma. I had a discussion with the specialist that I see for my glaucoma, and she changed my medication. My asthma improved dramatically after that.

    Don

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  3. What do you think of the idea of athletes floating in mgso4? Apparently, it gets absorbed through the skin and corrects a mg deficiency? And is it true that you cannot overdose on mag? Saw all this on a fb post by a naturopath.

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    • Athletes may need additional magnesium (beyond the RDA) and some forms of magnesium can be absorbed through the skin. This seems like it would be a costly method to counteract a deficiency. As for overdosing… It’s extremely unlikely that you’ll reach a level of toxicity through consumption of magnesium containing foods (the body regulates absorption based on need). However, it is possible to consume too much through supplementation, laxatives, or antacids. Elderly persons and people with kidney disease are most susceptible to magnesium toxicity.

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