Magnesium glycinate is one of the most requested forms on the market, and one of the most misunderstood when it comes to the label. Brands ask for “500 mg of magnesium glycinate” and then discover the Supplement Facts panel shows a much smaller number. Nothing went missing. The label is counting something different.
Compound weight vs elemental magnesium
Magnesium glycinate is magnesium bound to the amino acid glycine. Most of the weight of that compound is glycine, not magnesium. On a US Supplement Facts panel, the amount listed for a mineral is the elemental mineral, meaning the magnesium itself.
Fully reacted magnesium bisglycinate is roughly 14% elemental magnesium at most, and hydrated grades come in lower, often around 11 to 13%. So 500 mg of the compound delivers somewhere around 55 to 70 mg of magnesium. For comparison, magnesium oxide is about 60% magnesium, which is why it appears in so many low-cost products.
What this means for capsule count
Say you want 200 mg of elemental magnesium per serving. At 14%, that takes about 1,430 mg of magnesium bisglycinate. A size 00 capsule holds roughly 700 to 800 mg of a powder like this, depending on density. That is two large capsules at the very least, and in practice often three or four with a lower-assay grade. Many brands settle on a lower dose per serving, or move to a tablet, once they see the numbers.
Work this out before you design the label. Serving size, capsules per bottle, bottle size and cost all follow from it.
“Buffered” glycinate
Some magnesium glycinate on the market is labeled “buffered”. That usually means it is blended with magnesium oxide to raise the magnesium percentage, sometimes to around 20% or more. It fits more magnesium in each capsule and costs less.
Buffered material is a legitimate ingredient. The problem is the label. If a product says “100% chelated” or “pure glycinate” and the raw material contains oxide, the claim isn’t accurate, and that kind of mismatch has drawn recalls and class actions. If you use a buffered grade, list the sources honestly.
What to ask your manufacturer
- The raw material spec sheet. Is it fully reacted bisglycinate or buffered? What is the guaranteed magnesium assay?
- How the label number is calculated. Ask to see the math from compound weight to elemental magnesium, including any overage.
- Finished-product testing. Magnesium content should be tested on the finished product and shown on the COA.
- Fit with the format. Ask how many capsules or tablets per serving your target dose needs before you lock the label.
The takeaway
When you plan a magnesium glycinate product, start from elemental magnesium, not compound weight. Confirm whether the raw material is fully reacted or buffered, and make sure the label matches what is really in the bottle. It is far easier to settle this at the formula stage than after the labels are printed.
Sources
- NIH Office of Dietary Supplements, Magnesium Fact Sheet for Health Professionals (elemental magnesium content of supplement forms; upper limit of 350 mg/day from supplements for adults).
- US FDA, 21 CFR 101.36, Nutrition labeling of dietary supplements.