Vitamin B12 and Magnesium Together

Quick answer

Neither NIH fact sheet says vitamin B12 and magnesium change each other's absorption. Adults need 2.4 mcg of B12 and 310 to 420 mg of magnesium a day. What the two share is a weak point: labels link long-term use of acid-reducing medicines with poor B12 absorption and, rarely, low magnesium.^1,2,3,4

Key facts

Adults need 2.4 mcg of vitamin B12 a day and 310 to 420 mg of magnesium, depending on age and sex.^1,2
About 50% of a B12 dose of 1 to 2 mcg or less is absorbed, but only about 2% of a 500 mcg dose.⁵
In a meal study, the share of added magnesium absorbed fell from 65% to 11% as the amount rose, although the total absorbed still went up.⁶
The omeprazole label links long-term acid suppression with poor B12 absorption, and reports low blood magnesium rarely after at least three months.^3,4
Vitamin B12 has no upper limit. The upper limit for magnesium from supplements and medicines is 350 mg a day for adults.^1,2

What the sources say about the two together

We found no statement in the NIH fact sheets, or in any other source we read, that vitamin B12 changes how magnesium is absorbed or that magnesium changes how B12 is absorbed. No trial tested the two together against either alone. Our conclusion is limited to that: the sources are silent, not reassuring.^5,7

There is a more interesting overlap in how each nutrient gets into the body. In both cases the gut handles a small amount well and a large amount poorly, so the amount per dose changes how much you absorb. In both cases stomach acid also plays a part.^5,7

The same pattern in two different nutrients

Absorption falls as the amount taken at one time rises^5,6,8,9
	Vitamin B12	Magnesium
Small amount	About 50% at 1 to 2 mcg or less	65% at the lowest amount tested with a meal
Large amount	About 2% at 500 mcg, 1.3% at 1,000 mcg	11% at the highest amount tested with a meal
Why	Intrinsic factor, the carrier protein, is saturated at about 1.5 to 2 mcg per meal	The share absorbed is higher from several small amounts than from one large one

This is why a large B12 tablet delivers far less than its label suggests: only about 1.3% of a 1,000 mcg dose is absorbed. It is also why magnesium advice leans toward smaller amounts through the day. Neither source turns this into a rule about taking the two together.^5,9

Stomach acid matters for both, in different ways

Food contains B12 bound to protein, and stomach acid frees it before it joins intrinsic factor. B12 in supplements and fortified foods is already free, so it skips that step. For magnesium it is the form that decides. In laboratory tests, magnesium oxide barely dissolved in water and only 43% dissolved at peak acid levels, while magnesium citrate dissolved well even in plain water.^1,10

Magnesium citrate dissolves well even without stomach acid. In small human studies it raised magnesium in blood or urine more than magnesium oxide did, both after a single dose and after 60 days of daily use.^10,11,12

So a person with low stomach acid, which is more common in older adults, is most affected for food B12 and for oxide forms of magnesium. A free-form B12 supplement and a well-dissolving magnesium form avoid those weak points. Our Magnesium Glycinate is neither the oxide nor the citrate form compared in those tests, and the evidence on how well glycinate is absorbed is limited to a few small studies.^1,13,14

What each is graded for

Contributes to normal functioning of the nervous system*^5,15

Moderate evidence

NIH describes B12 as required for the development, myelination and function of the central nervous system; myelin is the coating around nerve fibers. The EU permits this statement. In trials summarized by NIH, B12 supplements given alone or with other B vitamins for 1 to 5 years did not change measures of memory and thinking in older adults.

Amount studied: Recommended intake: 2.4 mcg a day for adults, from all sources

Contributes to normal energy-yielding metabolism*^1,5,15

Moderate evidence

B12 is the helper for an enzyme that processes propionate, and NIH describes a role for it in energy metabolism. 'Contributes to normal energy-yielding metabolism' is the wording European regulators permit for vitamin B12. It does not mean extra B12 gives more energy: NIH notes that B12 supplements do not add energy, athletic performance or endurance in people who get enough from their diet.

Amount studied: Recommended intake: 2.4 mcg a day for adults, from all sources

Amounts and our products

Vitamin B12 and magnesium for adults, per day^1,2,5,16
	Vitamin B12	Magnesium
Recommended amount	2.4 mcg	310 to 320 mg for women, 400 to 420 mg for men
Typical supplements	5 to 25 mcg in multivitamins, 500 to 1,000 mcg in B12 alone	197 to 994 mg a day used in trials
Upper limit	None set	350 mg from supplements and medicines

What’s in ours

Men's Multi: Vitamin B12, 27 mcg per serving, from the label
Ashwagandha Complex: Vitamin B12, 25 mcg per serving, from the label

What’s in ours

Magnesium Glycinate: Magnesium, 275 mg per serving, from the label
Men's Multi: Magnesium, 50 mg per serving, from the label
Creatine + Electrolytes: Magnesium, 60 mg per serving, from the label

Magnesium counts toward its limit from every product, and our Men's Multi has some alongside its B12. The check below adds the label amounts for Men's Multi and Magnesium Glycinate taken on the same day.

Our Magnesium Glycinate with our Men's Multi

Magnesium Glycinate and Men's Multi together provide 325 mg of magnesium a day, close to the 350 mg upper limit for magnesium from supplements. Do not add another magnesium product.

One medicine can lower both

Acid-reducing medicines are the clearest shared risk. Proton pump inhibitors can reduce B12 absorption from food and, taken for a long time, lower blood magnesium. Loop and thiazide diuretics are linked to magnesium loss, and metformin to lower B12. If you take any of these, ask a pharmacist or doctor how to check both.^5,7

Your doctor may want to check on you

Proton pump inhibitors such as omeprazole and lansoprazole reduce stomach acid, which the body needs to release B12 from food. The omeprazole label says daily use of any acid-suppressing medicine for a long time, such as more than 3 years, may lead to poor absorption of B12.^1,3,5

On the medicine's label

Your doctor may want to check on you

Proton pump inhibitors such as omeprazole and esomeprazole can cause low blood magnesium when taken for a long time, usually more than a year. The omeprazole label says this has been reported rarely after at least three months and that doctors may check magnesium before and during long-term use.^2,4,7

On the medicine's label

Ask first if you have kidney disease or reduced kidney function, since the kidneys remove extra magnesium.⁷
Ask first if you have numbness or tingling in your hands or feet, balance problems or memory changes. These need testing rather than self-treatment.⁵
Ask first if you take an antibiotic, a bisphosphonate, gabapentin or levothyroxine, which magnesium can affect.^2,7
Ask first if you are pregnant or breastfeeding, especially if you eat no animal foods.⁵

Questions people ask

Can you take vitamin B12 with magnesium?

The sources we read describe no effect of one on the other, and many multivitamins contain both. Track the totals against the magnesium limit, and ask a pharmacist if you take acid-reducing medicines, diuretics or metformin.^5,7

Does magnesium reduce B12 absorption?

No source we read says so. Our sources describe B12 absorption as depending on intrinsic factor, and on stomach acid for the B12 in food. Magnesium is not named.^1,8

Is there a best time to take B12 and magnesium?

Neither NIH sheet names a time of day for B12. The only magnesium timing in our ingredient file comes from a sleep trial, where people took it 30 to 60 minutes before bed, and that does not apply to B12.^5,17

Which medicines can lower both B12 and magnesium?

Proton pump inhibitors such as omeprazole can reduce B12 absorption and, over a long time, lower blood magnesium. The omeprazole label describes both and says doctors may check magnesium during long-term use.^3,4

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See the Full Measure line Creatine + Electrolytes Magnesium Glycinate Men's Multi

Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.