No, it is not necessary to take calcium and magnesium together. In fact, if you need to take large amounts (250 mg or more) of either of these, it's best to take them at separate times, as they can compete with each other for absorption. For the same reason, it's best to take other minerals, such as iron and zinc, at a different time of day than calcium or magnesium. For more details, see the What to Consider When Using section of the Calcium Supplements Review, which includes our Top Picks among calcium supplements.

Also see our tests and Top Picks among magnesium supplements in our Magnesium Supplements Review.

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October 19, 2020

Question: How far apart (i.e., 1 hour, 2 hours, 4 hours)? Since this means, presumably, taking these apart not only from supplements but from high calcium/magnesium foods as well this gets awfully complicated. To get 1200 mg of calcium I need to take significant amounts throughout the day. When you consider that a similar rule applies to fat-soluble vitamins--which need to be taken with a high-fat meal--this gets pretty dizzying. Also: Does this mean that I should assume that some of the calcium/magnesium that occur together in food (i.e., milk) is not being absorbed?
October 20, 2020

Please see the "What to Consider When Using" section of the Calcium Supplements Review for details

October 21, 2020

Thanks for your reply. But after re-reading this section I am still unclear. Would it be the same 2-hour separation as recommended for iron and calcium? Would the same time frame apply to the fat soluble vitamins which compete for absorption?
Also: What happens with the Ca and Mg naturally occurring in foods? If I have a glass of milk and a peanut butter sandwich should I assume that some portion of the Ca in the milk or of the Mg in the milk and peanut butter is not being absorbed, and will not count toward my daily requirement--or has this been factored into the DVs?
October 21, 2020

Please keep in mind that competition for absorption is not an all-or-none proposition, so even if one mineral interferes with the absorption of another the amount of interference may not be clinically significant. In addition, nutrients naturally occurring in foods are absorbed more slowly than from supplements, as they must first be released from the foods, so they may not create as much competition for absorption as a supplement containing the same amount of that nutrient.

February 25, 2018

I would like to know where this rumour came from that you need to take magnesium and calcium together in order to make it work better. I have been under that impression for a long time and have heard it from my health-food store as well. But thanks for the good news anyway.
February 26, 2018

Hi Frauke - This idea may come from the fact that magnesium plays a role in proper calcium absorption. However, this means that you should make sure you get sufficient amounts of both each day -- not that they should be taken at the same time.

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