Taking zinc and magnesium together: what matters

Do you need to leave a gap between zinc and magnesium? The sources reviewed here give no basis for a blanket rule like that. What counts first is how much of each mineral you take in total on top of your diet. The frequently cited study on how the two affect each other used a very high amount of zinc. It does not translate into a general intake schedule for typical combination products. [1]

Where the warning about combining them comes from

In a metabolic study from 1994, adult men received an extra 142 mg of zinc a day. Across the groups studied, magnesium absorption and magnesium balance fell. The groups differed in their calcium intake, and the results were not the same in every group. [1]

So the finding concerns a high zinc intake. The study does not say whether the same thing happens at other amounts. It also did not compare a two-hour gap with taking both at once. A fixed separation rule cannot be derived from it.

Check the amounts first

Germany’s Federal Institute for Risk Assessment (BfR) proposes 6.5 mg of zinc per recommended daily serving of a food supplement. Above 3.5 mg, it recommends a label note advising against taking other zinc-containing supplements. These are proposals for how products should be formulated, not an individual dose and not a legal maximum. [2]

For magnesium, the BfR gives 250 mg per recommended daily serving of a food supplement, split into at least two portions. Magnesium from ordinary food does not count toward this additional amount. [3]

Three questions help when you compare labels:

Does the figure refer to one capsule or the whole daily serving?
Does a multivitamin, sports powder or second mineral product also contain zinc or magnesium?
Is the amount of the mineral itself listed, or only the mass of its chemical compound?

A worked example: if one product supplies 5 mg of zinc per daily serving and a second supplies 10 mg, that adds up to 15 mg extra. Taking them at different times of day does not change the total. The example is label arithmetic, not an intake recommendation.

Does combining them make both more effective?

Taking two things together and getting an added benefit are separate questions. A combination product can be convenient, but that alone does not mean any advantage for sleep, training or hormones.

A small study of 14 men who exercised regularly and already had adequate zinc intake found no significant rise in total or free testosterone after a ZMA product. Besides zinc and magnesium, ZMA also contains vitamin B6. The result applies to the group studied and the product used. It cannot support a general promise about testosterone. [4]

Medicines change the question

If you take medicines, comparing the two minerals with each other is not enough. Certain drugs come with their own interactions and timing gaps. Checking the package leaflet of the specific medicine is therefore more important than a universal supplement schedule. The examples in the magnesium interaction check show why “always leave two hours” would be too simple.

Frequently asked questions

Should zinc be taken in the morning and magnesium in the evening?
The zinc and magnesium study reviewed here does not support that rule. Any intake schedule a doctor has prescribed for you individually is not affected.

Is a combination product automatically the better choice?
No. With a combination product too, you need to establish whether the ingredients are needed and offer any added benefit. What matters is the composition, the daily amount and the reason for taking it.

Should I avoid zinc-rich foods because of this study?
The study is about high-dose zinc supplements. It is no reason to keep ordinary foods containing zinc and magnesium apart.

Sources

Spencer et al., 1994: zinc intake and magnesium balance: abstract reviewed; full text not reviewed.
BfR: proposed maximum levels for zinc: official risk assessment.
BfR: proposed maximum levels for magnesium.
Koehler et al.: ZMA and testosterone in physically active men: abstract reviewed.