Ferrous fumarate vs ferrous sulfate

At a glance

In the comparison of ferrous fumarate vs ferrous sulfate, ferrous sulfate carries more iron per gram: 36.8 % against 32.9 %, both on an anhydrous basis. To declare 100 mg of iron you need 272 mg of anhydrous ferrous sulfate or 304 mg of ferrous fumarate, about 12 % more powder. Ferrous sulfate dissolves in water and has a saline taste. Ferrous fumarate is only slightly soluble, and that difference usually decides the choice more than iron content does.

Both are among the iron sources covered in the iron forms guide.

Content per gram and label-claim arithmetic

The gap comes from the counter-ion. Each salt carries one iron atom, but anhydrous ferrous fumarate has a molar mass of 169.9 g/mol against 151.9 g/mol for anhydrous ferrous sulfate. The heavier fumarate dilutes the iron more.

The arithmetic is the same for any claim: powder mass = iron claim ÷ elemental fraction. For two example label claims:

These figures exclude overage. Add your overage separately, for example with the overage calculator.

The 36.8 % figure applies only to anhydrous FeSO4. Ferrous sulfate is also traded as hydrated and dried grades, and water of crystallisation lowers the iron per gram. A hydrated grade can carry less iron than ferrous fumarate. Always calculate from the iron assay on the certificate of analysis, using the elemental content calculator if needed.

At these masses either salt fits easily into a capsule. The difference matters mainly in multinutrient tablets where total mass is already tight.

Solubility, taste and processing

Ferrous sulfate dissolves readily, so it suits effervescent tablets and drink powders that must give a clear solution. The same property brings the drawbacks. Dissolved ferrous iron tastes saline and metallic, and it is reactive.

Ferrous sulfate is hygroscopic. With moisture and air, ferrous iron oxidises to ferric iron, which shows as yellow-brown discolouration. Control humidity during blending and compression, and use moisture-barrier packaging.

In multinutrient premixes, ferrous ions can accelerate the oxidation of ascorbic acid and other sensitive vitamins. Dissolved iron also reacts with polyphenols in botanical extracts, darkening blends and drinks. Stability testing of the finished product settles whether a combination works.

Ferrous fumarate’s slight solubility means less iron goes into solution in a moist blend or in the mouth. That generally makes it less reactive in premixes and less noticeable in chewable tablets. In liquids and effervescent formats it does not fully dissolve and leaves a sediment.

Colour is the other practical point. The brown to reddish-brown powder shows in white tablets and can cause speckling. A film coat or an opaque, coloured shell for capsules hides it. Flow and compressibility depend on the particle size of the grade, which the specification sheet states.

EU regulatory status

Annex II of Directive 2002/46/EC lists both ferrous fumarate and ferrous sulphate as iron sources permitted in food supplements. Both also appear in Annex II of Regulation (EC) No 1925/2006, which covers the addition of minerals to other foods. The permitted forms guide explains how these lists work.

There is no harmonised EU maximum level for iron in food supplements. Member states set their own limits, and they differ; see maximum levels by EU country.

On the label, Directive 2002/46/EC requires the amount of iron itself to be declared, not the mass of the salt. The ingredient list under Regulation (EU) No 1169/2011 names the form used. The labelling guide covers the details.

Authorised health claims and their conditions of use are in the EU Register of nutrition and health claims. The health-claims guide explains how to use it.

Choosing between them

• Clear liquids, effervescent tablets, drink powders: ferrous sulfate, because it dissolves.
• Chewable tablets and taste-sensitive formats: ferrous fumarate, because less iron dissolves in the mouth.
• Premixes with vitamin C or botanical extracts: ferrous fumarate is generally less reactive; confirm with stability data.
• Tight tablet mass: anhydrous ferrous sulfate saves about 12 % of powder. Compare actual certificate assays, since a hydrated sulfate grade may reverse this.
• White or pale tablets: ferrous sulfate shows less colour, though its oxidation can discolour over time.
• Cost: compare price per milligram of iron, not per kilogram of powder.

State the salt, hydration state and grade you need in the quote form. SoleChem sends the specification sheet and certificate of analysis with its quote.

Combining both salts in one product is rarely worthwhile. It adds a second specification and a second ingredient declaration without a technical gain. Using both across a range is common: ferrous sulfate in a drink powder and ferrous fumarate in a tablet, each declared by its own name.