Iron forms for supplement manufacturing

How the iron forms compare

This guide compares four iron forms used as raw materials in food supplements. Ferrous sulfate carries the most iron, 36.8 % on an anhydrous basis. Ferrous gluconate carries the least, 12.5 %. No single form of iron is best for every product. The right choice depends on label claim, format, taste, stability and regulatory status.

The content figures are for the anhydrous compounds. Ferrous sulfate is traded in hydrated and dried grades, and ferrous gluconate usually contains water of crystallisation. These grades carry less iron per gram than the table shows. Always calculate from the iron assay on the certificate of analysis, not from the formula.

Solubility drives most formulation behaviour. Ferrous sulfate and ferrous gluconate dissolve readily, which suits effervescent tablets and drinks. The free ferrous ions they release bring a metallic, astringent taste and react more readily with other ingredients. Ferrous iron oxidises to ferric iron in the presence of moisture and air, which can shift colour. Iron can also promote oxidation of unsaturated oils and some vitamins in a premix.

Ferrous fumarate is only slightly soluble, so it gives less taste in dry formats. Its brown to reddish-brown colour can show through light-coloured tablets and capsule shells. Iron pyrophosphate is a ferric compound and is generally regarded as less reactive than the soluble ferrous salts. Grades differ in solubility, so check the specification before choosing it for a liquid or effervescent product.

Choosing a form

• Label claim per unit. To declare 20 mg of iron per serving you need about 54 mg of anhydrous ferrous sulfate, 61 mg of ferrous fumarate or 160 mg of ferrous gluconate. At high claims, the mass of gluconate can exceed what a small capsule holds. The elemental content calculator repeats this arithmetic with the assay from your certificate.
• Format. Ferrous sulfate (dried grades) and ferrous fumarate give compact fills for tablets and capsules. Ferrous gluconate and ferrous sulfate dissolve fully in effervescent tablets. In gummies and powders, taste and reactivity usually decide, and iron pyrophosphate is worth evaluating.
• Moisture and stability. Ferrous sulfate is hygroscopic, so control humidity during blending and packing. As a reducing agent, ascorbic acid tends to keep iron in the ferrous state. Run stability tests on the finished product for colour and assay whatever the combination.
• Taste. The soluble ferrous salts taste metallic. This matters most in chewables, drinks and loose powders. Coated or encapsulated grades, or a less soluble form, reduce the problem.
• Cost per milligram of iron. Ferrous sulfate and ferrous fumarate are usually the most economical per milligram of iron. Ferrous gluconate needs about 2.6 times more powder than ferrous fumarate for the same claim, which raises cost per milligram. Iron pyrophosphate is usually chosen for technical reasons rather than cost.
• Regulatory status. Each form must appear in the EU list of permitted mineral substances, set out below.

For a direct side-by-side of the two most common tablet forms, see ferrous fumarate vs ferrous sulfate. Other mineral salts are grouped under Minerals & Mineral Salts. SoleChem sends the specification sheet and certificate of analysis with each answer to the quote form, so the iron assay and hydrate form are known before you fix the formula.

EU regulatory status

Food supplements in the EU fall under Directive 2002/46/EC. Annex I lists iron among the minerals that may be used. Annex II lists the iron substances that may be used to supply it. Ferrous fumarate, ferrous gluconate, ferrous sulphate and ferric diphosphate (ferric pyrophosphate) appear in Annex II. Confirm that the iron pyrophosphate you buy is the ferric compound named there. The guide to permitted vitamin and mineral forms explains how to read the annex.

Ferrous gluconate also has the food-additive number E 579 under Regulation (EC) No 1333/2008, which sets out the foods in which it may be used as an additive. Check its additive specification in Regulation (EU) No 231/2012. When it is added to a supplement as a source of iron, it is used as a mineral substance under Directive 2002/46/EC.

Directive 2002/46/EC provides for EU maximum amounts of minerals, but none have yet been set. Member states apply their own maximum levels for iron, and these differ. The guide to maximum levels by EU country explains how to find them. The label declares the amount of iron, not the salt, in milligrams; see labelling a food supplement in the EU. For authorised claim wording, consult the EU Register of nutrition and health claims and the health claims guide.