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Magnesium: Are you low, but don’t know?

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Jana is a 50-year-old woman with three children at various stages of leaving the nest … and returning to the nest … and leaving again. She comes into my office, not surprisingly, with high blood pressure and annoying afternoon headaches. She already takes a medication to reduce her blood pressure, and really doesn’t want to take another. She’s wondering if there might be something else wrong and if there are drug-free ways to feel better.

My first thought for Jana is magnesium. People who are depleted in magnesium will have higher blood pressure, higher blood sugar, more headaches and muscle cramping, worse anxiety, and trouble sleeping. It’s easy to overlook recommending magnesium, especially if lab results are within normal range.

The downside to magnesium is its common side effects, including loose stools, abdominal cramping and bowel urgency. Paying attention to the dose could be helpful in reducing unwanted gastrointestinal symptoms. Here is some general advice for considering magnesium.

  • What are Jana’s risk factors for magnesium deficiency? Jana has a few risk factors for being magnesium deficient. She eats an American diet, which is commonly depleted of magnesium from being industrially produced and over processed. She is also taking hydrochlorothiazide, which is a common, first line treatment for high blood pressure. This medication is well recognized for lowering potassium in the body, but it also affects magnesium. If Jana drinks alcohol — even socially — this puts her at risk of magnesium deficiency. Although not an issue for Jana, another risk factor for magnesium deficiency is the use of nonprescription medications to manage heartburn and gastroesophageal reflux disease (GERD), such as proton pump inhibitors (PPIs).
  • Is it possible to get enough magnesium from food? Yes, but it may not be in sufficient amounts. Many healthy foods are rich in magnesium, including nuts, beans, seeds and dark chocolate.
  • Why not just check magnesium blood levels? This is trickier than you might think. A blood test of magnesium may not provide a helpful answer. Magnesium is a charged mineral in the body and resides primarily inside the cell. When you test for magnesium in the blood, you are checking the level outside the cell. If the level is low, your magnesium is low. If it’s normal, you don’t know. There is a lab test that checks intracellular magnesium. However, it’s expensive and not typically covered by insurance.
  • Who should not take magnesium? Anyone with kidney disease — that is, disease that affects the kidney function — should not take magnesium unless recommended and monitored by a clinician. In addition, some people cannot tolerate magnesium because of the gastrointestinal (GI) side effects.
  • What kind of magnesium is best? For people who struggle with slow bowel movements or constipation, any magnesium supplement should be fine. If you have loose, frequent stools or irritable bowel syndrome, consider using magnesium glycinate — a specific salt of magnesium that tends to have fewer GI side effects.
  • What is the best dose of magnesium? Many people take magnesium at night because they find it calming. But it can be taken at any time of day. The typical dose is 250 to 500 milligrams daily.
  • How long should it be taken? I recommend taking magnesium for at least three months before deciding whether it does or does not work. At that point, if you perceive a benefit, keep taking it. If it hasn’t helped, you can probably stop.

Denise Millstine, M.D.

Dr. Millstine is a women’s health internist and integrative medicine specialist at Mayo Clinic in Scottsdale, Arizona, where she lives with her husband and twin sons. She serves on the Editorial Board for the Mayo Clinic Health Letter and is the Medical Director for the women’s health blog on Mayo Clinic Press. Find her on Twitter @drdmaz

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