Calcium and magnesium: together or apart?
Futures Nutrition Editorial Team · 12 August 2026
Calcium and magnesium: together or apart?
The short answer: at the amounts found in food supplements, calcium and magnesium can be taken together — a time gap between the two is not necessary. What actually counts are the portion sizes: for food supplements the German Federal Institute for Risk Assessment (BfR) proposes no more than 500 mg of calcium and 250 mg of magnesium a day — with magnesium expressly spread across two or more portions.
Before that, however, comes a question that gets lost in the combination-product aisle: whether both are short in the first place. Calcium and magnesium are covered to different degrees in Germany, and they are not short in the same people. Anyone who supplements both because they are sold together is often topping up nothing at all on one of the two.
Why the question is asked as a pair question
Because the two almost always stand side by side on the shelf — and often in the same tablet, with "2:1" on the front. That figure comes from a recommendation that meant an upper limit for total daily intake and was not a mixing instruction for a product; where it comes from and why it cannot carry a purchasing decision is set out at length in Magnesium and calcium: reading the 2:1 ratio.
Nothing follows from it for the way the two are taken. A ratio is not a rule about when you swallow what. And in the EU there is no authorised claim that links the two minerals to each other either: what is authorised are statements about each one separately — Calcium is needed for the maintenance of normal bones and teeth. Magnesium contributes to normal muscle function. (Regulation (EU) No 432/2012). Sentences claiming that magnesium is what gets calcium "to the right place" are not on the list.
Two nutrients, two separate calculations
The German National Nutrition Survey II recorded for both minerals how much is actually eaten. The figures sit side by side in the BfR's maximum-level opinions — and they look different for calcium and for magnesium.
| Calcium | Magnesium | |
|---|---|---|
| D-A-CH reference value, adults | 1,000 mg per day | 350 mg (men) / 300 mg (women) |
| Nutrient reference value on the label | 800 mg | 375 mg |
| National Nutrition Survey II, median men | 1,052 mg | 389–454 mg by age group |
| National Nutrition Survey II, median women | 964 mg | 334–378 mg by age group |
| National Nutrition Survey II, 25th percentile | 808 mg (m) / 755 mg (f) | — |
| National Nutrition Survey II, 95th percentile | 2,061 mg (m) / 1,734 mg (f) | 596–809 mg (m) |
| BfR proposed maximum level for food supplements | 500 mg per day | 250 mg per day |
With magnesium, then, the average intakes lie throughout in the region of the reference values. With calcium the median is at or above the reference value in almost every age group — with two exceptions the BfR names explicitly: female adolescents aged 14 to 18 and 65- to 80-year-olds of both sexes.
At the same time, the right-hand half of the distribution shows that calcium is the nutrient where supplementation swings upwards fastest: at the 95th percentile young men reach 2,422 mg a day through diet alone and thereby use up 97 % of the tolerable total intake of 2,500 mg (SCF 2003, confirmed by EFSA in 2012). For magnesium no such limit for intake from food exists at all — the 250 mg apply solely to what is added on top through a preparation.
In practice this means the decision is made separately for each of the two. Keeping notes for a few days on what goes on the plate settles it faster than any rule of thumb — the portion figures for that are in Daily calcium needs: 800 mg label, 1,000 mg advised.
What happens when both are in the stomach at once
The worry that calcium blocks magnesium absorption comes predominantly from animal experiments. In humans it is less well supported than the widespread advice "leave at least two hours between them" suggests.
The cleanest investigation of this is a double-blind balance study from the American Journal of Clinical Nutrition (Andon et al., 1996). Twenty-six girls with an average age of 11.3 years received a controlled basal diet containing 667 mg of calcium and 176 mg of magnesium over 14 days — plus either 1,000 mg of additional calcium or a placebo. The result: magnesium balance did not differ between 667 and 1,667 mg of calcium a day.
That is the decisive order of magnitude. Hardly anyone taking a 200 or 500 mg tablet reaches 1,667 mg of calcium a day. A time gap between a calcium and a magnesium preparation therefore solves a problem that does not arise at usual amounts.
Where gaps genuinely do count: in relation to iron and zinc preparations and to certain medicines — calcium and magnesium can affect their absorption. What applies there is in the package leaflet, not in a guide.
Portion size is the real adjusting screw
Instead of watching the clock, it is worth looking at the amount per intake. For both minerals the same holds, for different reasons: smaller and more often beats large and once.
With calcium, the proportion absorbed falls as the single portion grows. Robert Heaney and colleagues measured a mean absorption of 36.0 % from a 300 mg portion in Osteoporosis International in 1999, and only 28.4 % from 1,000 mg. Anyone supplementing a larger daily amount gets more out of it by spreading it across two occasions. On top of that comes the question of the compound: calcium carbonate needs stomach acid and therefore belongs with a meal, citrate does not — as set out in Calcium forms: carbonate, citrate, gluconate.
With magnesium, the reason is tolerability. The tolerable maximum of 250 mg additionally per day was derived by the EU Commission's Scientific Committee on Food from mild diarrhoea occurring in a small proportion of adults from around 360 to 365 mg; more recent indications already name 300 mg. Because the underlying studies worked with divided doses, the figure applies expressly to two or more portions a day — the BfR adopts this recommendation for food supplements. How tightly this limit is to be read is set out in Too much magnesium: reading the 250 mg limit.
For calcium the BfR has additionally drawn a threshold for individual products: above 250 mg of calcium per daily serving it recommends a note on the pack advising against further calcium-containing food supplements. Anyone combining two preparations should therefore do the arithmetic instead of simply adding up whatever happens to be in the cupboard.
A daily plan if you take both
| Time | What fits there | Why |
|---|---|---|
| Breakfast | calcium portion, mandatory with a meal for carbonate | acid dissolves the salt; a smaller portion is proportionally better absorbed |
| Midday | first magnesium portion | division as recommended by the BfR |
| Evening | second magnesium portion, if needed a second calcium portion | spread instead of a bolus; the time of day is freely chosen for both |
| Keep a gap | from iron and zinc preparations and, as per the package leaflet, from medicines | an effect on absorption is described there |
Between calcium and magnesium themselves this table deliberately shows no gap. The division in the plan follows tolerability and the absorption rate, not a competition between the two.
What counts on the label
What is compared is always the mineral, not the salt. The nutrition declaration states the amount of calcium or magnesium in milligrams — the figures on the front ("1,000 mg calcium citrate", "500 mg magnesium citrate") refer to the weight of the compound and are several times higher than the mineral contained.
Our Calcium + vitamin D3 4,000 IU supplies 200 mg of calcium per tablet — 25 % of the nutrient reference value — and thereby stays below the BfR's 250 mg threshold. The recommended intake is one tablet daily after a meal.
We stock magnesium separately from this, for instance as magnesium bisglycinate 150 mg with 150 mg of elemental magnesium per tablet, that is 40 % of the nutrient reference value. Compared with a combination tablet, two separate products have the advantage that one amount can be changed without changing the other along with it. An overview of all the minerals is in the minerals category.
Food supplements are not a substitute for a balanced and varied diet and a healthy lifestyle.
Frequently asked questions
Do I have to leave a gap between calcium and magnesium? Not at usual amounts. In Andon's balance study (1996), raising calcium from 667 to 1,667 mg a day did not change magnesium balance. Spreading intake across the day still makes sense — with magnesium because of tolerability, with calcium because of the absorption rate.
Is a combination product worse than two separate ones? Not as a matter of principle. It is more convenient and usually cheaper, but it ties the two amounts to each other. Anyone who is already well supplied with one of the two nutrients — with calcium that is the majority according to the National Nutrition Survey II — is using a combination tablet to top up a part they do not need.
Why is the magnesium limit 250 mg and the calcium one 500 mg? Because the two figures measure different things. The 250 mg for magnesium are a tolerable maximum for additional intake, derived from a mild, temporary laxative effect. The 500 mg for calcium are a BfR proposal for food supplements that takes into account that the diet already covers a large part of the total intake of up to 2,500 mg.
I take both and have loose stools — what causes that? Most probably the magnesium: mild diarrhoea is the first undesirable effect of excessive additional intakes and the reason for the 250 mg limit. Splitting the daily amount into two portions is the obvious first step; with impaired kidney function both minerals belong in medical hands anyway.
Sources: German Federal Institute for Risk Assessment, "Proposed maximum levels for calcium in foods including food supplements" — maximum level 500 mg per day for food supplements, note recommended from 250 mg per daily serving, UL 2,500 mg (SCF 2003, EFSA 2012), D-A-CH reference values, National Nutrition Survey II percentiles for calcium; German Federal Institute for Risk Assessment, "Proposed maximum levels for magnesium in foods including food supplements" — maximum level 250 mg per day spread across two or more portions, SCF UL (2001) for additional intakes, derivation from mild diarrhoea from 360/365 mg and indications from 300 mg (Roffe et al. 2002; Supakatisant and Phupong 2015), D-A-CH and EFSA reference values, National Nutrition Survey II medians for magnesium; Max Rubner Institute, German National Nutrition Survey II, results report part 2 (2008); Andon MB, Ilich JZ, Tzagournis MA, Matkovic V, "Magnesium balance in adolescent females consuming a low- or high-calcium diet", Am J Clin Nutr 1996;63(6):950–953 (PMID 8644692); Heaney RP, Dowell MS, Barger-Lux MJ, "Absorption of calcium as the carbonate and citrate salts, with some observations on method", Osteoporos Int 1999;9(1):19–23 (PMID 10367025); Regulation (EU) No 1169/2011, Annex XIII (nutrient reference values 800 mg calcium, 375 mg magnesium); Regulation (EU) No 432/2012 (official wording of the authorised claims); composition according to the label of the products named.
