Magnesium is an essential mineral that doesn’t get the attention it deserves. You’d be hard pressed to find any activity in the body that doesn’t use magnesium in some way. It has literally hundreds of functions.
Cellular energy production, protein synthesis, DNA and RNA synthesis, and cell signaling—which controls the secretion of certain hormones, among other things—all depend on magnesium. It plays an important role in ion channels that allow nerves to fire, potassium and sodium to cross cellular membranes, and muscles to contract. Production of ATP, the energy currency of the body, depends on magnesium. Your heart beats rhythmically thanks to magnesium.
Not surprisingly, then, magnesium deficiencies seem to factor into a wide range of health issues. Let me tell you about some of the biggies.
Health Issues Related to Magnesium
Before getting into the details, I want to draw your attention to a few challenges with the research literature. One, which I’ll return to later, is that magnesium levels in the body are tough to measure.
Second, lots of studies try to link dietary magnesium intake to specific health outcomes. Foods that contain magnesium, like leafy greens and fish, also contain a host of other vitamins and minerals, fiber, sometimes amino acids. This makes it hard to isolate the effects of any single nutrient.
The way magnesium intake is measured, usually with the Food Frequency Questionnaire (FFQ) or food diaries, is also fraught with error. I don’t put too much stock in studies that correlate dietary intake with any specific health outcome. Correlation doesn’t prove causation anyway, as you know. I’ll mention them here to give you a complete picture of what researchers are working with. Ideally, though, I like to see randomized controlled trials.
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Magnesium and Inflammation
It’s increasingly clear that inflammation is at the heart of many, if not most, chronic disease states. Studies have shown that people who consume less than half the recommended daily allowance of magnesium have higher levels of C-reactive protein (CRP), a marker of inflammation.
1  Magnesium intake negatively correlated with CRP in two large observational studies, the Women’s Health Initiative Study 2  and the NHANES Study 3 .
These observations are supported by experimental studies which, according to a 2018 meta-analysis. confirm that magnesium supplementation lowers CRP levels4 
The Link Between Heart Health and Magnesium
There are many well-documented metabolic pathways through which magnesium can affect heart health. Magnesium may reduce heart disease risk by reducing arterial stiffness, improving endothelial function5 , and/or lowering chronic inflammation. It also inhibits platelet aggregation, which is itself a risk factor for heart disease.6 
Several large prospective studies have correlated higher magnesium intake or higher magnesium levels in the blood with reduced risk of cardiovascular disease and stroke.7  8  9  10  Magnesium deficiency is considered a risk factor for cardiac arrhythmia and hypertension (high blood pressure).
A recent review of the available evidence concluded that while it’s fair to say that magnesium intake is important for cardiovascular health overall, more randomized controlled trials are needed to understand the particulars better.11 
It’s also too soon to conclude that supplementing would have any specific effects, although there is some promising evidence when it comes to hypertension. Two meta-analyses found overall positive, though inconsistent, benefits for lowering blood pressure.12  13  Magnesium supplementation can also be used alongside blood pressure meds to increase their effectiveness.14 
Type 2 Diabetes and Insulin Sensitivity
Magnesium affects how cells take up glucose out of the bloodstream, glucose oxidation, and insulin sensitivity.15  Researchers estimate that 25 to 38 percent of type 2 diabetics are deficient in magnesium.16 
Diabetes and magnesium deficiency is a vicious cycle. Prospective studies suggest that people with lower magnesium intake are at greater risk for insulin resistance17  and developing type 2 diabetes18 . Once they have the disease, they lose more magnesium through urine, making them more susceptible to ongoing magnesium deficiency. This then exacerbates the problems of poor glucose management and insulin resistance, increasing the chances of diabetic complications.19 
A 2016 review and meta-analysis showed that magnesium supplementation improves fasting glucose in folks with type 2 diabetes. Among folks who are at risk of developing the disease, supplementing leads to better glucose tolerance and insulin sensitivity. However, the authors also noted a high degree of variability in the data.20  A second meta-analysis found better insulin sensitivity and fasting glucose, particularly when supplementation lasted at least four months.The results of this analysis also indicate that the effects are greatest among people who start out with low magnesium.21 
Magnesium and Bone health
Low magnesium is associated with low calcium, impaired parathyroid hormone secretion, low vitamin D, and inflammation. This adds up to a perfect storm when it comes to developing osteopenia and osteoporosis. On the other hand, chronically high magnesium levels may demineralize bones and put people at risk for fracture.22 
In correlational studies, dietary intake is positively associated with bone mineral density in postmenopausal and premenopausal women 23 , older men and women24 , and older white, but not Black, folks 25 . However, magnesium levels in the blood don’t consistently correlate with bone mineral density like you’d predict.
Magnesium and Migraines
A fair number of studies find that migraine sufferers have lower magnesium levels than people who don’t get migraines.29  Although migraines are still not well understood overall, scientists have proposed a variety way low magnesium contributes to migraines, including by affecting inflammation and vasodilation, among others.
Research also points to magnesium supplementation as an effective option for managing migraines. Children30  and adults31  with a history of migraines reported fewer and less severe episodes when supplementing with magnesium. One impressive study found that when people went to the emergency room with migraines, magnesium provided even more relief than drugs.32 
The American Academy of Neurology and the American Headache Society agree that magnesium is probably effective for the treatment of migraines.33 
The authors of a 2012 paper even went so far as to argue that all migraine sufferers should be taking magnesium.34 
Magnesium Could Help with Depression and Anxiety
Magnesium has many complex actions in the brain, including affecting neurotransmitter and hormone release and neuronal firing. Although research provided promising evidence a century ago that magnesium can be used to treat depression, nobody took much notice.35  Even now there aren’t a ton of studies.
In a 2017 review of 18 studies, about half reported that magnesium supplementation alleviated anxiety symptoms.40 
But Wait, There’s More!
More research is needed, but magnesium may be a factor in:
What about Sleep?
Magnesium supplementation is often touted for sleep, but there’s actually not that much direct evidence that it helps. One small study involving 12 elderly participants concluded that magnesium supplementation enhanced sleep quality.45  In another study of 46 elderly insomnia patients, eight weeks of magnesium supplementation significantly improved sleep quality and quantity.46  That’s about it.
Still, many sleep aids  contain magnesium because it is needed to convert 5-HTP to serotonin, which in turn converts to melatonin. It also blocks NMDA receptors in the brain and promotes GABA, both of which are important for sleep. (These same mechanisms may explain why magnesium helps with depression, by the way. Some scientists have also suggested magnesium’s action on NMDA receptors is why it alleviates migraines.)
Magnesium plays a key role in glucose metabolism and energy production. Since glucose is mobilized during exercise, it makes sense that magnesium would be important. Research in mice shows that giving them magnesium increases the amount of available glucose during exercise. It also delays the accumulation of lactate in the muscles, which may prevent fatigue.47 
The evidence for using magnesium supplementation to improve human performance is mixed. For example, in one study, male professional volleyball players were able to jump higher, and they had decreased lactate production, after supplementing magnesium for four weeks.48  Triathletes likewise improved their swim, bike, and run times.49  However, another study found no benefit for marathoners.50 
Even if it doesn’t yield a performance benefit, though, it’s clearly important that athletes make sure their electrolyte intake is sufficient. More on that next week.
Normal Levels and Magnesium Deficiencies
It’s difficult to test magnesium levels. The most common method is a blood test. Normal serum concentrations fall between 0.75 and 0.95 mmol/L.
However, less than 1 percent of total body magnesium is in the bloodstream, and serum level is tightly regulated by the kidneys, as well as bone and intestines. Blood tests are poor indicators of total body magnesium levels. Your doctor may use a combination of blood, saliva, and urine tests if they suspect a severe deficiency . No single method seems to work very well.
Clinical deficiencies in healthy adults are rare, but data from the large NHANES study suggests that perhaps only one-third of Americans hits the recommended daily intake.51  If true, many people may be walking around with sub-optimal magnesium levels. People who are at greater risk for deficiencies include those with gastrointestinal issues such as Chron’s or celiac disease that interfere with nutrient absorption, diabetes, kidney disease, or who take certain medications. The elderly and people with alcoholism often have low magnesium
Severe deficiencies can be indicated by low calcium and potassium levels, and by non-specific symptoms like muscle spasms and vomiting. Mild deficiencies usually have no noticeable symptoms.
The recommended daily intake for adults is 310 mg for females aged 19 to 30, and 320 mg thereafter. For males, it’s 400 mg up to age 30, then 420 mg. Pregnant women need an extra 40 mg per day.
Does Diet Matter?
Possibly. If you’re following a keto diet, you should supplement  with sodium, potassium, and magnesium. You need up to an additional 300 to 500 mg of magnesium per day.
I’ve also previously  considered  whether folks following a carnivore diet may need less magnesium from their food, perhaps because they consume less glucose or fiber than omnivorous types. I think it’s too soon to tell, although I’m open to the possibility.
Foods High in Magnesium
Some of the best Primal-friendly sources of magnesium include:
- Leafy greens: spinach, Swiss chard
- Dark chocolate
- Nuts: almonds, cashews
- Seeds: pumpkin, hemp, watermelon
- Fish: halibut, mackerel, salmon
In addition to food sources, as much as 10 percent of our magnesium intake comes from drinking water.52 
How to Choose a Magnesium Supplement
As with any nutrient, it’s best to get magnesium from food. The Food and Nutrition Board of the US Institute of Medicine designates 350 mg/day as the tolerable upper intake level (UL) for supplementing.
When choosing a magnesium supplement, look for a chelated form, the ones ending in -ate. They have the best bioavailability. Magnesium glycinate and malate are both good choices. Magnesium citrate is probably the most common since it is inexpensive and widely studied, but it can have undesirable laxative effects for some people. L-threonate is particularly noted for its cognitive benefits. Avoid large doses of magnesium oxide unless you specifically want diarrhea; opt for smaller doses spread out across the day.
Certain pharmaceutical drugs can interact with magnesium. Talk to your doctor, especially if you take medications for osteoporosis or HIV, if you are on a diuretic, or if you are prescribed tetracycline or quinolone antibiotics.
Can You Get Too Much Magnesium?
While magnesium toxicity is possible, it’s very rare. Most forms of magnesium will cause gastrointestinal distress before that point. Stick to recommended doses, though.
Transdermal Magnesium: Epsom Salts Baths and Magnesium Oil
Both epsom salt baths  (magnesium sulfate) and magnesium oil sprays (usually magnesium chloride) are touted as alternatives for boosting magnesium levels. However, there is almost no research verifying that it is effectively absorbed through the skin.53  Still, many people use them for recovery from exercise, relief from pain or cramping, and as sleep aids.
If it works for you, by all means keep doing it. However, if you’re looking for a guaranteed way to increase magnesium levels, it’s safer to go with a supplement.
Some Important Things to Keep in Mind
We covered a lot of ground today. Before I let you go, let me point out a couple of things.
First, as with most—probably all—vitamins and minerals, there’s a sweet spot with magnesium. Too little is clearly bad, but trying to cram in more than you need is not good either.
That said, some of the experiments referenced here used doses that are well above the 350 mg UL for supplementation. Don’t go mega-dosing on your own, of course. On the other hand, if you’re considering using magnesium to help with a specific health issue, consult your doctor to see how much you might need to see results.
Though it’s clear that magnesium is a big-time player in optimal health overall, more research is needed to understand the specific benefits. My guess is that most Primal folks eating a diverse diet are getting enough magnesium. If you’re curious, use a food tracking app like Cronometer  to see how much you get over the course of several days to a week.
Stay tuned next week. I’m planning to talk more generally about electrolytes and when and why you’d want to supplement. Let me know if you have any questions along those lines.