Calcium vs Magnesium: what to choose and for whom

Calcium, magnesium or a complex of both - the choice depends on your diet, age, training and state of health. The editorial team has put together a practical guide: who should think about calcium, who about magnesium, which forms to choose, how to avoid interactions with medications, and when supplements are not needed at all.

Start with the diet, not the jar

Calcium and magnesium are among the most popular mineral supplements, but most people can get enough of them from food. So before choosing between calcium, magnesium or a combined product, it is worth assessing what is really lacking in your diet. This is cheaper and safer than taking everything at once.

Calcium in the diet mostly comes from dairy products, hard cheese, sardines and small fish with bones, fortified plant drinks, tofu with a calcium coagulant, and some kinds of greens. If you eat several servings of dairy products a day, a calcium deficiency is unlikely.

Magnesium is found in nuts, seeds (especially pumpkin), legumes, whole grains, cocoa and dark leafy greens. A diet dominated by refined products - white bread, sweets, fast food - is often poor precisely in magnesium, even if calories are sufficient.

So if you consume little dairy - pay attention to calcium; if little whole plant food - to magnesium. And if the diet is varied, a supplement may not be needed at all.

Who needs calcium more

Additional calcium is most often needed by people who do not consume dairy products: vegans, people with lactose intolerance or an allergy to cow's-milk protein. A group of attention is also postmenopausal women, for whom the norm rises to 1200 mg per day, and the elderly (Ross et al., 2011).

Among athletes, calcium is especially important for women with low energy availability and menstrual cycle disorders, who have an increased risk of stress fractures. The ACSM position (Thomas et al., 2016) classes calcium, together with vitamin D, among the key micronutrients for athletes' bone health.

Practical rules for taking calcium as a dietary supplement, described in the review by Straub (2007):

• absorption is best when the single serving does not exceed about 500 mg of elemental calcium;
• calcium carbonate is taken with food, citrate - independently of food;
• on the label count precisely the elemental calcium, not the mass of the salt;
• account for calcium from food so that the total does not exceed the upper limit - 2500 mg per day up to age 50 and 2000 mg after.

Calcium should not be taken "as a reserve." The meta-analysis by Bolland and colleagues (2010) linked calcium supplements with an increased risk of myocardial infarction. Although this topic is debatable, it is an argument in favor of getting calcium mainly from food and taking supplements only when needed.

Who needs magnesium more

Magnesium is more often lacking in people with a diet poor in whole foods, those who sweat a lot during prolonged training in the heat, and people who take certain medications. Long-term use of proton pump inhibitors and certain diuretics can lower magnesium levels, so such patients should discuss monitoring with a doctor.

In athletes, benefit from magnesium supplements is most likely in the presence of a low baseline status. The review by Zhang and colleagues (2017) showed that the data on the effect of magnesium on performance are contradictory, and positive effects were more often observed in people with insufficient intake. For a person with a full diet, magnesium will hardly add strength or endurance.

As for cramps, expectations should be adjusted: the Cochrane review by Garrison and colleagues (2020) did not confirm the effectiveness of magnesium for the prevention of ordinary muscle cramps in the elderly. Cramps in athletes are more often associated with muscle fatigue and the specifics of the load.

The tolerable upper level of magnesium specifically from supplements (not counting food) is 350 mg per day for adults (Institute of Medicine, 1997). Exceeding it most often manifests as diarrhea. For people with impaired kidney function, magnesium supplements are contraindicated without a doctor's supervision, because magnesium can accumulate in the blood.

Combined products and choice of form

"Calcium + magnesium" complexes (often with vitamin D and zinc) are convenient but not always rational. The ratio in such products is determined by the manufacturer, while your real needs may be different: for example, you lack only magnesium, and there is enough calcium from food. Then the complex adds an unnecessary mineral.

The physical aspect matters too: a lot of calcium is needed, so complex tablets are often large, and the serving is split into several tablets. Separate products allow you to more precisely select the amount of each mineral and distribute the intakes throughout the day.

Among the forms of magnesium for daily intake, citrate or glycinate are often chosen because of better tolerability; oxide is cheaper but more often causes digestive upset. For calcium, the choice between carbonate and citrate depends on whether you take it with food and whether you have reduced stomach acidity.

Interactions and safety

Calcium and magnesium bind to many medications in the intestine and reduce their absorption. This applies to tetracyclines and fluoroquinolones, levothyroxine, bisphosphonates. Between taking such preparations and mineral supplements an interval of several hours is needed - the exact time should be clarified with a doctor or pharmacist.

Calcium also reduces the absorption of iron, so people who take iron at the same time should space these supplements out in time. Large doses of both minerals simultaneously can compete for absorption, which is another argument in favor of distributing the intakes.

Excess calcium from supplements can contribute to constipation and, in susceptible people, the formation of kidney stones. Excess magnesium from supplements more often manifests as diarrhea, and in people with kidney failure - as dangerous hypermagnesemia. So chronic kidney disease is a direct indication for consultation before taking them.

Laboratory monitoring for these minerals has limitations: the level of calcium in the blood is tightly regulated and says little about the diet, while serum magnesium poorly reflects its stores in the tissues. So assessment of nutrition and the clinical picture are often more important than a single test.

Editorial conclusions

Calcium should be considered primarily by people who do not consume dairy products, postmenopausal women and female athletes with a risk to their bones. Magnesium - by those whose diet is poor in whole plant foods, who sweat heavily or take medications that lower its level.

The "calcium + magnesium" complex is convenient but not always necessary: often one mineral or simply a correction of the diet is enough. One should not expect from either of them a gain in athletic performance or a guaranteed relief from cramps.

Before taking supplements, people with kidney and heart disease and those taking continuous medications should consult a doctor.

To better understand the differences between the minerals, read "Calcium or Magnesium: what is the difference." We also recommend our articles on vitamin D for athletes and on electrolytes during prolonged training.

References

1. Ross AC, Taylor CL, Yaktine AL, Del Valle HB (eds); Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington (DC): National Academies Press; 2011.
2. Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington (DC): National Academy Press; 1997.
3. Straub DA. Calcium supplementation in clinical practice: a review of forms, doses, and indications. Nutr Clin Pract. 2007;22(3):286–296.
4. Zhang Y, Xun P, Wang R, Mao L, He K. Can magnesium enhance exercise performance? Nutrients. 2017;9(9):946.
5. Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and athletic performance. Med Sci Sports Exerc. 2016;48(3):543–568.
6. Bolland MJ, Avenell A, Baron JA, et al. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. BMJ. 2010;341:c3691.
7. Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2020;9:CD009402.