Magnesium: one mineral, 300+ jobs.
Poor sleep. Muscle cramps. Constipation. Headaches. When people tell me about these, magnesium is one of the first places I look. Here's what it does, the forms I reach for, and how to find out where you stand.
Ask your doctor for an RBC magnesium test, not just the standard serum test.
Less than 1% of your body's magnesium is in your blood serum, and your body works hard to hold that number steady. So serum can look normal while the stores in your tissues run low. RBC magnesium measures what's inside your red blood cells, a closer look at the magnesium your cells actually hold. No single test is perfect, and researchers still debate the best one, but RBC adds information a serum test can't.1,6,7
Why magnesium matters
Magnesium is a working part in more than 300 enzyme systems. It helps turn food into usable energy, lets muscles relax after they contract, steadies nerve signals and heart rhythm, and supports blood sugar balance. It's needed to build bone, make DNA and protein, produce glutathione, and activate vitamin D. Some researchers now count more than 600 enzymatic reactions. One mineral, hundreds of jobs, and one of the most commonly under-consumed minerals in modern diets.1,4,5,8,9
- Energy (ATP) production
- Protein and DNA synthesis
- Bone structure
- Nervous system and stress response
- Muscle relaxation and heart rhythm
- Blood sugar balance
- Glutathione production for detoxification
- Regular bowel movements
What people commonly report
These have many possible causes. They're a reason to look, not a diagnosis. If you have several of them and have never had your magnesium checked, that's where I'd start.
Commonly reported
- Trouble falling or staying asleep
- Muscle cramps, tension or twitches
- Constipation
- Headaches
- Fatigue and weakness
- Low appetite or nausea
See your doctor promptly
More serious deficiency can cause:
- Numbness or tingling
- Abnormal heart rhythm
- Personality changes
- Seizures
What the research says about those four
How to find out where you stand
More than 99% of your magnesium lives inside your cells and bones, not in your blood, which is why the test you choose matters.1,6,7
The test most often run. It measures the small amount in the liquid part of your blood, which your body keeps in a tight range. Good at catching significant deficiency, but it can read normal while tissue stores are low.
Measures magnesium inside your red blood cells, a window into what your cells are holding. Not a perfect measure, but a useful addition to serum. Ask for it by name. It's offered by major national labs.
Measures the free, active form in your blood. Useful, but less widely available.
Shows how much magnesium your kidneys release or hold on to. Used in more specialized situations.
Talk with your doctor about which test fits you. Want to order labs yourself? See Lab Testing.
Not all magnesium is the same
Magnesium is always bound to a partner molecule. That partner changes how well it's absorbed, how it feels in your gut, and what it's best for.2,10,11
Bound to glycine, an amino acid studied on its own for sleep quality.14 Gentle on the stomach, with little laxative effect.
Well absorbed; in one head-to-head trial it outperformed oxide and a chelate.10 Draws water into the bowel, which helps with constipation. Higher amounts loosen stools.
Malate takes part in the energy-producing cycle inside your cells. A good daytime choice; direct research on this form is limited.
Developed to raise magnesium in the brain in animal research,12 with a small human study on cognitive function in older adults.13 Less magnesium per capsule and more expensive.
Paired with taurine, which also supports heart rhythm and calm nerve signaling. Research on this specific form is still early.
Lots of magnesium per tablet but poorly absorbed, about 4% in one study,10,11 so much of it stays in the gut and acts as a laxative.17 Not my choice for rebuilding stores.
Well absorbed by mouth.2,11 Often sold as a spray or bath flakes, though absorption through skin isn't well proven.16
A calming ritual, but evidence that meaningful magnesium crosses the skin is limited.16 Taken by mouth it's a laxative, not a daily supplement.
Label tip: compare products by elemental magnesium per serving, not the total weight of the compound. That's the amount of magnesium you actually get.
How magnesium works
Eat your magnesium
Seeds, nuts, beans, leafy greens and whole grains are your richest sources. A small handful of pumpkin seeds covers roughly a third to half of your daily need.1
Supplements fill gaps. They don't replace a plate built on whole foods.
| Food | Serving | Magnesium |
|---|---|---|
| Pumpkin seeds, roasted | 1 oz | 156 mg |
| Chia seeds | 1 oz | 111 mg |
| Almonds, dry roasted | 1 oz | 80 mg |
| Spinach, boiled | ½ cup | 78 mg |
| Cashews, dry roasted | 1 oz | 74 mg |
| Peanuts, oil roasted | ¼ cup | 63 mg |
| Black beans, cooked | ½ cup | 60 mg |
| Edamame, shelled, cooked | ½ cup | 50 mg |
| Potato, baked with skin | 3.5 oz | 43 mg |
| Brown rice, cooked | ½ cup | 42 mg |
Source: NIH Office of Dietary Supplements1
How much, and when to be careful
Recommended daily intake (food + supplements)
| Adults | 19–30 yrs | 31+ yrs |
|---|---|---|
| Men | 400 mg | 420 mg |
| Women | 310 mg | 320 mg |
| Pregnancy | 350 mg | 360 mg |
The upper limit for magnesium from supplements and medications is 350 mg a day for adults. Magnesium from food doesn't count toward that limit. Going higher should be guided by your practitioner.1,2
Be careful if…
- Loose stools are the first sign you're taking more than your body can absorb. Lower the amount or switch forms.
- You have kidney disease. Don't take magnesium without your doctor's approval.
- You take bisphosphonates or certain antibiotics. Magnesium can block their absorption, so space them apart. Ask your pharmacist about timing.
- You take long-term acid reducers or certain diuretics. These can lower magnesium levels over time.
The magnesium I actually recommend
These are the forms and brands I use with patients. Each is chosen for quality, purity and the right form for the job.
My specific product picks are being added. In the meantime, everything I recommend is in my virtual dispensary.
Professional-grade supplements, all in one order
Browse the brands and products I trust and order several at once, shipped to your door.
Some links are affiliate or dispensary links, which means I may earn a commission at no extra cost to you.
Not sure which magnesium fits you?
References
- National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. ods.od.nih.gov
- National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Consumers. ods.od.nih.gov
- Harvard T.H. Chan School of Public Health. The Nutrition Source: Magnesium. nutritionsource.hsph.harvard.edu
- de Baaij JHF, Hoenderop JGJ, Bindels RJM. Magnesium in man: implications for health and disease. Physiol Rev. 2015;95(1):1-46. PubMed
- Rosanoff A, Weaver CM, Rude RK. Suboptimal magnesium status in the United States: are the health consequences underestimated? Nutr Rev. 2012;70(3):153-164. PubMed
- DiNicolantonio JJ, O'Keefe JH, Wilson W. Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis. Open Heart. 2018;5(1):e000668. PubMed
- Jahnen-Dechent W, Ketteler M. Magnesium basics. Clin Kidney J. 2012;5(Suppl 1):i3-i14. PubMed
- Uwitonze AM, Razzaque MS. Role of magnesium in vitamin D activation and function. J Am Osteopath Assoc. 2018;118(3):181-189. doi.org
- Franklin CC, Backos DS, Mohar I, White CC, Forman HJ, Kavanagh TJ. Structure, function, and post-translational regulation of the catalytic and modifier subunits of glutamate cysteine ligase. Mol Aspects Med. 2009;30(1-2):86-98. PubMed
- Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res. 2003;16(3):183-191. PubMed
- Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001;14(4):257-262. PubMed
- Slutsky I, Abumaria N, Wu LJ, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165-177. (Animal study.) PubMed
- Liu G, Weinger JG, Lu ZL, Xue F, Sadeghpour S. Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. J Alzheimers Dis. 2016;49(4):971-990. PubMed
- Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007;5(2):126-131. doi.org
- Abbasi B, Kimiagar M, Sadeghniiat K, Shirazi MM, Hedayati M, Rashidkhani B. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. J Res Med Sci. 2012;17(12):1161-1169. PubMed
- Gröber U, Werner T, Vormann J, Kisters K. Myth or reality—transdermal magnesium? Nutrients. 2017;9(8):813. PubMed
- Mori S, Tomita T, Fujimura K, et al. A randomized double-blind placebo-controlled trial on the effect of magnesium oxide in patients with chronic constipation. J Neurogastroenterol Motil. 2019;25(4):563-575. PMC
- Holland S, Silberstein SD, Freitag F, Dodick DW, Argoff C, Ashman E. Evidence-based guideline update: NSAIDs and other complementary treatments for episodic migraine prevention in adults. Neurology. 2012;78(17):1346-1353. PubMed
- Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2020;9(9):CD009402. PubMed
This page is for educational purposes only and is not a substitute for professional medical diagnosis, treatment, or advice. These statements have not been evaluated by the Food and Drug Administration. Products mentioned are not intended to diagnose, treat, cure, or prevent any disease. Talk with your healthcare provider before starting a supplement, especially if you are pregnant, nursing, take medications, or have a medical condition.