What it is
Magnesium takes part in a large number of enzymatic reactions, including energy production, muscle contraction and nerve transmission. The recommended intake for adults falls between 310 and 420 mg per day depending on age and sex. People buy it mostly for sleep, cramps and stress.
What the label does not say
- The NIH specifies that the nutrition facts table declares elemental magnesium, not the weight of the whole compound. A number on the front of the bottle that corresponds to the weight of the salt is therefore not the magnesium dose.
- The upper limit of 350 mg per day applies only to magnesium from supplements and medications. Health Canada writes that it represents intake from a pharmacological agent only and does not include intake from food and water. It therefore cannot be compared with the recommended intake of 400 mg, which does include food.
- The forms most heavily promoted on store shelves are not always the ones the NIH names as better absorbed.
- Prolonged use of proton pump inhibitors, generally beyond one year, is associated with hypomagnesemia. A supplement does not fix the cause.
The forms on the shelf
- Oxide and sulfate: the NIH describes them as less well absorbed than the other forms.
- Citrate, lactate, chloride and aspartate: the four forms the NIH describes as more completely absorbed, because they dissolve better in liquid.
- Bisglycinate: very common on store shelves, but it does not appear on the NIH fact sheet's list of better-absorbed forms.
Published reference values
- Recommended intake for adults: 400 mg per day from 19 to 30 and 420 mg from 31 onward for men; 310 mg from 19 to 30 and 320 mg from 31 onward for women.
- Upper limit: 350 mg per day, supplements and medications only.
- Above that, the most frequently reported effect is diarrhea, sometimes with nausea and abdominal cramps.
When
Can be taken at any time of day. Spacing it from certain medications matters more than the hour you choose.
Keep apart from
- Bisphosphonates (alendronate): at least 2 hours apart.
- Tetracyclines (doxycycline): at least 2 hours before or after.
- Quinolones (ciprofloxacin): 2 hours before or 4 to 6 hours after.
To mention to a professional
- Kidney failure, prolonged use of proton pump inhibitors or diuretics, pregnancy and breastfeeding: check with a health care professional before supplementing.
From the plate first
According to the NIH: 156 mg per ounce of roasted pumpkin seeds, 111 mg per ounce of chia seeds, 80 mg per ounce of almonds, 78 mg per half cup of boiled spinach, 74 mg per ounce of cashews.
Sources
- NIH Office of Dietary Supplements, Magnesium (Health Professional)
- Health Canada, Dietary Reference Intakes, reference values for elements
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.