Calcium is certainly critical for bone health.
Still, the evidence that high calcium intakes reduce fracture risk is not very strong.
That evidence comes from population studies that link intakes of 1,000mg per day or more to reduced risk for fractures.
Likewise, more-reliable evidence from clinical trials hasn’t proven that supplemental calcium is significantly effective for fracture prevention.
And high-dose supplemental calcium raises the risk for kidney stones and heart attacks, and can cause nausea and stomach upset.
High calcium intakes also make it harder for your body to absorb magnesium.
That’s a real problem, given Americans’ generally low magnesium intakes — see "Magnesium shortfalls: Common and quiet", below — and the mineral’s importance to bone, mood, immune, metabolic, and heart health.
We covered research from those realms in Heartening Magnesium News, Women's Risk of Sudden Death Linked to Magnesium, Magnesium's Anti-Diabetic Gene Effects, Diabetes Linked to Magnesium Lack, Magnesium May Cut Stroke and Diabetes Risks, and Magnesium Shortage Speeds Aging.
Five years ago, review of the evidence from 40 epidemiological studies — involving about 1 million people — linked each 100 mg per day rise in magnesium intake to a 7% drop in the risk of stroke, and drops of 22%, 19% and 10% in the risks of heart failure, type 2 diabetes, and death from any cause, respectively. Those apparent benefits did not increase further with daily intakes of 500 mg or more.
Getting back to bones, two recent studies linked higher magnesium intakes to reduced fracture risk among men and women alike.
Study #1 — Higher magnesium intakes linked to better bone health
Last month, a British-Italian team published findings that back the power of magnesium to help prevent fractures.
They examined diet and health data from 3,765 older Americans (aged 60 years or more), and linked the highest average magnesium intakes to the lowest risk for suffering a bone fracture over an eight-year period (Veronese N et al. 2017).
Compared to the participants with the lowest average intakes, the men with the highest estimated intakes (398 mg per day) were 53% less likely to suffer a fracture.
Better yet, the women with the highest estimated intakes (373 mg per day) were 62% less likely to suffer a fracture.
However, the risk reduction only reached statistical significance for women, after the results were adjusted to account for each volunteer’s height, which is a risk factor for fractures.
(In the second bone study we’re reporting on today, men with high magnesium intakes showed more benefit.)
The researchers noted that only 27% of the participants were estimated to consume the USA RDA of 420mg for men and 320mg for women (see the RDA table below).
U.S. RDAs for Magnesium
And, compared with women who were getting less magnesium, the risk of fracture for women estimated to be consuming the RDA level or more was significantly lower.
As the researchers wrote, “[H]igher dietary [magnesium] intake has a protective effect on bone osteoporotic fractures, particularly in women, suggesting an important role of this mineral in osteoporosis and fractures.” (Veronese N et al. 2017)
In an accompanying editorial, Dr. Richard Hayhoe of the University of East Anglia put the findings into helpful context:
“Despite mounting epidemiological evidence of the positive association of magnesium intake and bone mineral density, data showing an association between dietary Mg intake and fracture risk has until now been unconvincing. The study ... thus provides a useful addition to the literature supporting the relevance of dietary intake of magnesium to osteoporotic fracture risk ...”. (Hayhoe RP 2017)
Study #2 — More backing for magnesium versus fractures
Three months ago, scientists at the Universities of Bristol and Eastern Finland collaborated on a separate population study (Kunutsor SK et al. 2017).
They analyze data collected from 2,245 middle-aged Finnish men (aged 42-61 years) in the Kuopio Ischemic Heart Disease study, whose health, blood chemistry, and diets had been recorded for 20 years.
Their analysis showed that men with higher magnesium levels were 44% less likely to suffer a fracture.
Conversely, men with lower blood levels of magnesium were more likely to suffer fractures, particularly in the hip.
None of the 22 men who had very high magnesium blood levels (more than 2.3mg per deciliter) experienced a fracture during the 20-year study.
Although the men’s estimated magnesium intakes didn’t (unlike their blood levels) predict their risk for fractures, that finding fit with those of several prior studies — except some, like the British-Italian study described above (Study #1).
Why would that be? As we noted above — see “Magnesium shortfalls: Common and quiet” — certain health factors can prevent magnesium-providing foods from raising blood levels substantially.
In such cases, people may need to take well-absorbed forms of supplemental magnesium (see “What about supplements?”, below).
Lead researcher Jari Laukkanen from the University of Eastern Finland summarized the implications of their and prior research findings:
“The overall evidence suggests that increasing serum magnesium concentrations may protect against the future risk of fractures; however, well-designed magnesium supplementation trials are needed to investigate these potential therapeutic implications.”
Magnesium and heart health
Last year saw the publication of three studies that seem to support the value of magnesium for heart health.
First, a review of the clinical evidence concluded that people people who consumed about 368 mg of magnesium for about three months enjoyed modest drops in blood pressure, with the clearest effects seen among people deficient or low in magnesium (Zhang X et al. 2016).
Second, a 25-year study of middle-aged Finnish men — also published last year — linked lower magnesium levels to a greater risk of future congestive heart failure (Kunutsor SK et al. 2016).
Finally, a nine-year study involving 9,820 older Dutch men and women found that those with the lowest blood magnesium levels (0.8 mmol/L or less) were 36% more likely to die from coronary heart disease and 54% more likely to succumb to sudden cardiac death, versus those with moderate (0.81 to 0.88 mmol/L) levels.
Compared with moderate levels, people in that Dutch study who had high magnesium levels (above 0.89 mmol/L) were 6% less likely to acquire coronary heart disease.
However, people with high magnesium levels were 35% more likely to succumb to sudden cardiac death (Kieboom BC et al. 2016).
Frankly, we'd take that last finding with a grain of salt, because it contradicts all the other findings, and doesn't make much biological sense. That said, it seems wise not to overdo magnesium — or any other dietary supplement.
Magnesium, brain-health, and mood
A recent clinical trial found that magnesium may ease depression, remarkably rapidly.
As its authors wrote, “Magnesium is effective for mild-to-moderate depression in adults. Effects were observed within two weeks.” (Tarleton EK et al. 2017)
It’s possible the mineral’s mood-elevating potential stems from its ability to reduce inflammation — as confirmed in a recent evidence review — because inflammation promotes depression (Simental-Mendía LE et al. 2017).
Magnesium supplements containing magnesium-L-threonate are promoted for improving memory or preventing memory loss, based primarily on animal studies.
Magnesium-L-threonate is to be the only form shown to significantly raise magnesium levels in the central nervous system, and in rodent studies, it enhanced brain processes associated with the ability to store information.
The sole, small clinical study of magnesium's effects on memory in people involved magnesium-L-threonate, and was funded by the makers of the supplement, called Magtein or Clarimem.
In that trial, men and women with anxiety, insomnia, and impaired memory or concentration took 1.5 to 2 grams of magnesium-L-threonate daily for three months. Compared with those who took a placebo, they displayed an average 10% rise in speed on a test of "executive" functions.
However, the participants who took magnesium-L-threonate showed no improvement in memory, attention, anxiety or sleep (Liu, J Alzheimer's Dis 2015).
Magnesium shortfalls: Common and quiet
Three out of four Americans do not get the recommended intakes of magnesium, and many have low blood levels of the mineral.
Magnesium blood levels in the U.S. range from 0.7 to 0.91 mmol/L (1.7 to 2.2 mg/dL).
Low magnesium levels are especially common among middle-aged to elderly people, who — perhaps not coincidentally — are also more prone to fractures.
Most people with low magnesium levels don’t show any signs or symptoms, and
magnesium levels are not routinely measured in blood drawn during hospital and doctor visits.
The amounts of magnesium in your food (and water) are not the only factors that determine your blood levels of magnesium.
For example, higher dietary levels of magnesium may not raise blood levels in people over 60, those with certain bowel disorders, and people taking certain medicines.
In those cases, it’s important to treat the underlying reasons for low blood levels — and supplemental magnesium may help raise and maintain them.
So, we hope that the fracture-prevention findings reported here will prompt inclusion of blood magnesium screening in routine blood tests, especially for people in late middle age or older.
Encouragingly, greater media attention to the mineral has prompted predictions that sales of supplemental magnesium will surpass calcium sales by 2020.
Top magnesium sources
Fish, leafy greens, nuts, seeds, grains, and foods high in fiber are relatively high in magnesium.
Other good food sources include yogurt, avocado, bananas, milk, chicken, legumes (beans and lentils), red meat, and seaweed.
This table shows the magnesium content of various foods (USDA data):
What about supplements?
Conventional wisdom calls for taking about one part magnesium to two parts calcium.
But other researchers argue, persuasively, that a one-to-one ratio is healthier, given the overload of calcium in most Americans' diets, and the lack of magnesium.
Also, prehistoric diets seem to have provided the minerals in a one-to-one ratio, suggesting that this ratio is what humans evolved in response to.
Finally, magnesium aids calcium absorption into bones, but the opposite is not true, with excess calcium impeding magnesium uptake.
Seek out supplements that provide magnesium in the most easily absorbed forms, which include magnesium citrate, chloride, chelate (lysinate or diglycinate), lactate, gluconate, aspartate, and glycinate.
Magnesium can exert laxative effects, and the forms typicaly used for this purpose are hydroxide and sulfate, which are not normally used for supplements. Magnesium citrate is used in supplements, and can exert significant laxative effects.
Magnesium carbonate and oxide are not well absorbed, while magnesium oxide can irritate the digestive tract. Magnesium orotate is very costly and does not offer any proven absorption advantage.
Magnesium supplements may cause stomach upset, nausea, vomiting and diarrhea.
Supplemental intakes above the recommended upper limits can cause thirst, low blood pressure, drowsiness, muscle weakness, and slowed breathing.
The upper supplemental intake limit for adults is 350mg per day for adults. (This is lower than some of the adult RDAs for total magnesium intake from foods and supplements, which range from 310mg to 420mg — see the RDA table above.)
People with kidney disease, severe heart disease, or severe intestinal disease should not take magnesium or any other mineral supplements without medical supervision.
Magnesium can impair the absorption of certain antibiotics, statin drugs, anti-diabetes drugs, and a drug prescribed for atrial fibrillation.
Magnesium can exert anti-coagulant/anti-platelet effects, so people taking blood-thinning medications should consult with their physician before taking magnesium.
Magnesium should be taken two or more hours before or after taking statin drugs, especially Crestor (rosuvastatin calcium).