Oxide, citrate, chelate: why the form on a label matters

Exhibit 01

The bracket after the name is the actual product

A Supplement Facts panel names a nutrient and then, in brackets, the compound it is delivered as. The word before the bracket is the element. The words inside it are what is actually in the capsule.

This label fills that bracket in on six of its seven nutrients — every line but the biotin — and four of them are worth setting side by side before any of them is judged.

The figure a panel prints is the weight of the element itself: 125 mg of magnesium means 125 mg of magnesium, not 125 mg of magnesium oxide powder. So the amount is honest whichever salt is used. What changes with the salt is the proportion of that weight that gets absorbed, and no panel publishes that.

Exhibit 02

Magnesium oxide, at 125 mg and 30% of the Daily Value

NIH is direct about magnesium forms, and it names the oxide specifically. Here are the two sentences, verbatim.

Forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms.

magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate

Magnesium oxide is what this label prints. The 125 mg is not untrue and the 30% is right against the 420 mg Daily Value NIH publishes. What the panel cannot tell you is how much of those 125 milligrams crosses the gut wall, and NIH publishes no percentage for magnesium the way it does for zinc, so this comparison is a direction rather than a figure.

The amount is well under NIH’s supplemental upper limit of 350 mg a day, the figure at which “high doses of magnesium from dietary supplements or medications often result in diarrhea that can be accompanied by nausea and abdominal cramping”. So the form is not a caution. It is a value question: the same printed 125 mg would deliver more in a citrate, and only the word in the bracket says so.

Exhibit 03

Zinc oxide, at 8 mg and 73% of the Daily Value

With zinc, NIH publishes the comparison as a pair of percentages, which makes this the one place on this label where the gap can be put in numbers.

Absorption of zinc from supplements that contain zinc citrate or zinc gluconate is similar, at approximately 61% in young adults; the absorption from supplements that contain zinc oxide is 50%.

Apply that to what is printed. Eight milligrams of zinc as the oxide, at the 50% NIH gives, is about four milligrams expected to be absorbed. The same eight as a citrate or a gluconate, at approximately 61%, is about five. That is the whole of the finding: one milligram. The 8 mg is also a long way under NIH’s upper limit of 40 mg, which matters because “If used for weeks, doses of 50 mg zinc or more can interfere with copper absorption (which can cause low copper status), reduce immune function, and lower HDL cholesterol levels.”

One more thing has to sit beside any mention of zinc on a blood sugar product. NIH reports that “The supplements reduced fasting glucose, 2-hour postprandial glucose, fasting insulin, insulin resistance, glycated hemoglobin, and C-reactive protein levels.” and then concludes: “Overall, the evidence to date is insufficient to support any conclusions about the impact of zinc supplementation on the prevalence or severity of type 2 diabetes.” Both halves belong on the page.

Exhibit 04

Why this is an absorption point and not a safety point

This distinction is the reason the post exists, so it gets its own exhibit rather than a line at the end.

Both oxides are ordinary, legal and widely sold. Nothing in the sources this site cites describes either one as unsafe, and both amounts sit comfortably under the upper limits NIH publishes. Nobody should read this post and stop taking a mineral.

What the oxides are is less completely absorbed than the alternatives NIH names. Our sources say nothing about what any of these forms costs, so neither does this post. A label printing a percentage against an oxide is quoting the weight in the capsule, which is the only thing a panel is required to quote. The number is an input, not an outcome.

Exhibit 05

Where this label names the natural form, and gets no credit for it

A site that only ever reported the cheap choice would be as useless as one that never did. This panel names the naturally sourced form once, visibly, and nothing in the marketing draws attention to it.

The vitamin E line reads Vitamin E (as d-alpha tocopheryl acetate). NIH explains the distinction: “Naturally sourced vitamin E is called RRR-alpha-tocopherol (commonly labeled as d-alpha-tocopherol); the synthetically produced form is all rac-alpha-tocopherol (commonly labeled as dl-alpha-tocopherol).”

The letter is the whole point. This label prints d-, the naturally sourced form, and the one a reader who does not know that a single letter carries it would walk straight past. At 16 mg against a 15 mg Daily Value, the 107% is the mildest over-100% figure on the panel.

The one caution on that line is about the reader rather than the amount: NIH records that “Taking large doses with anticoagulant or antiplatelet medications, such as warfarin (Coumadin), can increase the risk of bleeding, especially in conjunction with low vitamin K intake.” 16 mg is nowhere near a large dose, the upper limit being 1,000 mg, but anyone on an anticoagulant has a short conversation to have with a prescriber.

The chromium is the third case. The panel prints Chromium Amino Acid Chelate, a named salt rather than the bare word chromium. Our sources publish no absorption comparison for that chelate, so this site can neither credit it nor criticise it.

Exhibit 06

What to look for in the bracket, on any panel

Four questions, in order. They take about fifteen seconds once you have done them twice, and they work on any Supplement Facts panel.

1. Is there a bracket at all?

   A panel that prints Magnesium and a number has told you less than one that prints Magnesium (as Magnesium Oxide).

2. What is inside it?

   The salt or the ester. Oxide, citrate, gluconate, chelate, acetate. This is the word that decides what the printed weight is worth.

3. Is there a letter doing work?

   On vitamin E, d- is the natural form and dl- the synthetic one, which NIH spells out. One character, two different products.

4. Does a published source compare the forms?

   NIH does for magnesium and for zinc. Where it does not, as with this chromium chelate, nothing can be said.

Run those four on this label and the fair summary is one sentence: two oxides, one natural-source vitamin E, one named chelate, and six checkable amounts that are all arithmetically correct. The ingredients page takes all nineteen ingredients one at a time.