Magnesium in pregnancy: evidence and safety

How does magnesium work?

Magnesium acts as a cofactor, and broadly so. NIH ODS places it in more than 300 enzyme systems regulating protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation, and describes it as required for energy production, oxidative phosphorylation, and glycolysis. It also plays a role in the active transport of calcium and potassium ions across cell membranes, the process underlying nerve impulse conduction, muscle contraction, and normal heart rhythm. Choosing the oxide form changes none of that biology. It changes how much magnesium arrives, since ODS notes that forms dissolving well in liquid are more completely absorbed and that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide.

What does the evidence say about magnesium in pregnancy?

• The pregnancy Recommended Dietary Allowance for magnesium is 350 to 360 mg a day, and the supplemental upper limit is 350 mg a day, not counting magnesium from food. 1
• Diarrhea, nausea, and stomach cramping are the most common side effects of going over the supplemental magnesium limit, so easing into your dose matters even within the 'safe' range. 2
• Magnesium oxide is a common supplement form, but your body absorbs only around 4 percent of it, so the same milligram amount delivers less usable magnesium than glycinate or citrate would. 1
• Oral magnesium can interact with several medications, including bisphosphonates, certain antibiotics like tetracycline and quinolones, and some diuretics. 1
• Pregnancy Smart's Supplement Facts panels list magnesium, as magnesium oxide, at 171 mg per three-capsule serving in Nausea and Digestive Support and 256.5 mg per three-capsule serving in Immune and Respiratory Support. 3

What's on the label?

The form named on the panel predicts both absorption and how your gut responds to it. ODS lists magnesium carbonate, chloride, gluconate, and oxide as the forms most commonly reported to cause diarrhea, and names aspartate, citrate, lactate, and chloride as better absorbed than oxide. Because the 350 mg supplemental upper limit counts only magnesium from supplements and not magnesium from food, the panel milligrams across every product you take are the numbers to add together.

• Nausea and Digestive Support lists Magnesium at 171 mg per serving, as printed on the Supplement Facts panel.
• Immune and Respiratory Support lists Magnesium at 256.5 mg per serving, as printed on the Supplement Facts panel.

When comparing any brand, read the Supplement Facts panel for the exact per-serving amount and look for third-party test results. Add any prenatal-vitamin amount of the same ingredient to your daily total before comparing against a pregnancy upper limit.

What should I know before taking magnesium?

Please consult your healthcare provider before starting, stopping, or stacking supplements in pregnancy, especially if you take prescription medication, live with a chronic condition, or have a procedure or delivery scheduled. Herbal supplements are not required to demonstrate purity; brands that publish third-party test results give the most confidence in what is actually in the capsule.