A study published in *The Journal of Nutrition* in 2025 analysed how two forms of oral iron – ferrous bisglycinate and ferrous sulphate – affected the gut microbiota in Cambodian women of reproductive age. The randomised controlled trial involved 144 non-pregnant women over a 12-week period. The main finding was that neither form of iron increased colonisation by Group B Streptococcus compared with the placebo.
This result has practical implications for those evaluating iron supplementation. Concerns that oral iron might negatively alter the gut microbiota were not confirmed in this population. Both forms showed a similar profile in terms of their impact on the bacteria studied.
What the trial on ferrous bisglycinate and ferrous sulphate in women aged 18 to 45 showed
The group receiving ferrous bisglycinate took 18 mg of elemental iron per day. The ferrous sulphate group received 60 mg daily, a dose three times higher. After 12 weeks, ferritin levels were comparable between the two groups, with a prevalence of iron deficiency of 0% in both active arms compared with 6% in the placebo group.
This finding is significant. Ferrous bisglycinate achieved comparable results in terms of iron status parameters at a significantly lower dose. This is consistent with the higher bioavailability characteristic of chelated forms of iron compared with inorganic salts such as sulphate.
Why the form of iron determines how much the body absorbs
Iron from the diet and from many supplements competes with phytates, oxalates and other compounds present in plant-based foods. These inhibitors form complexes with non-haem iron and reduce its intestinal absorption. Ferrous sulphate, being an inorganic salt, is particularly vulnerable to these interactions.
Ferrous bisglycinate is an organic chelate. The iron is bound to two molecules of the amino acid glycine, which protects the mineral during its passage through the digestive tract and promotes its absorption via a different pathway to that of non-chelated iron. According to published clinical evidence, bisglycinate can achieve up to four times greater absorption than ferrous sulphate in diets rich in phytates. Furthermore, its good digestive tolerance sets it apart from conventional ferrous salts, which frequently cause stomach upset or constipation.
How Nutribiolite’s Iron Complex follows the physiological logic of the study
The study used ferrous bisglycinate as the experimental form of oral iron in adult women. Nutribiolite’s Iron Complex uses exactly this same form, ferrous bisglycinate, as its source of iron. The alignment between the form studied and that used in the product is no coincidence: it follows the same logic of prioritising actual bioavailability over high doses of forms with lower absorption.
The formula also includes vitamin C, which enhances iron absorption, and B-group vitamins in their bioactive forms: vitamin B6 as pyridoxal-5-phosphate, vitamin B12 as methylcobalamin, and folate as L-5-MTHF. These forms do not require prior metabolic conversion to be utilised by the body, which represents a real advantage over standard forms such as folic acid or cyanocobalamin. Vitamin B2, also present in the formula, plays a role in the normal metabolism of iron and in the maintenance of red blood cells. The product contains no unnecessary synthetic colourings or additives, and the capsules are plant-based, making it suitable for vegans.
Nutribiolite’s Iron Complex combines highly absorbable ferrous bisglycinate with vitamin C, vitamins B6, B2 and B12, and active folate (L-5-MTHF) in pure vegetable capsules, free from synthetic additives.
How each nutrient in the Iron Complex contributes to the normal formation of red blood cells and energy metabolism
Iron contributes to the normal formation of red blood cells and haemoglobin, to the normal transport of oxygen and to normal energy metabolism. Vitamin C enhances iron absorption and contributes to the normal functioning of the immune system. Vitamin B6 plays a role in the normal formation of red blood cells and helps reduce tiredness and fatigue. Vitamin B2 supports normal iron metabolism and the maintenance of red blood cells in a normal state. Vitamin B12 contributes to the normal formation of red blood cells and to the reduction of tiredness and fatigue. Folate in the form of L-5-MTHF supports normal blood formation and the process of cell division.
The recommended dose of one capsule a day for up to four months ensures sustained and consistent supplementation. Consistency is a key factor in ensuring that iron supplementation has a real impact on haematological parameters.
Why active folate (L-5-MTHF) is particularly important for women of reproductive age
Folate plays a particular role in women who are planning a pregnancy or who are already pregnant. Insufficient maternal folate intake is a risk factor for neural tube defects in the foetus. European health authorities state that the beneficial effect is achieved with a supplementary intake of 400 µg of folate per day for at least one month before conception and up to three months afterwards.
Each capsule of Nutribiolite Iron Complex provides 400 µg of folate in the form of L-5-MTHF, equivalent to 200% of the reference nutritional value. This form can be utilised directly by the body, unlike standard folic acid, which requires prior enzymatic conversion—a process not everyone carries out with the same efficiency. For women in the preconception phase or during pregnancy, it is advisable to consult a healthcare professional before starting any supplementation.
Frequently asked questions about iron and ferrous bisglycinate supplementation
How does ferrous bisglycinate differ from ferrous sulphate in terms of absorption?
Ferrous bisglycinate is an organic chelate in which iron is bound to two glycine molecules. This structure protects it from dietary inhibitors, such as phytates, and promotes its absorption via a different pathway to that of non-chelated iron. According to clinical evidence, it can be absorbed up to four times more effectively than ferrous sulphate in diets rich in phytates. Furthermore, its good digestive tolerance makes it particularly suitable for people who are sensitive to other forms of iron.
Why is it important to include vitamin C alongside iron in a supplement?
Vitamin C enhances the absorption of non-haem iron by reducing ferric iron to its ferrous form, which the intestine absorbs more easily. Nutribiolite’s Iron Complex contains 80 mg of vitamin C to optimise the utilisation of the 20 mg of ferrous bisglycinate in each capsule, as well as contributing to normal energy metabolism and the normal functioning of the immune system.
What does it mean when the product’s B vitamins are in bioactive forms?
The bioactive forms – B6 as pyridoxal-5-phosphate, B12 as methylcobalamin and folate as L-5-MTHF – are the forms that the body can utilise directly without the need for prior metabolic conversion. This is particularly important for people with genetic variants that make it difficult to process standard forms such as folic acid or cyanocobalamin.
Is this iron supplement suitable for people on a vegan or vegetarian diet?
Plant-based iron, known as non-haem iron, is absorbed less efficiently than iron of animal origin. Vegans and vegetarians may find it more difficult to meet their iron requirements through diet alone. Nutribiolite’s Iron Complex is suitable for vegans, with a vegetable-based capsule and no ingredients of animal origin, and provides iron in the form of bisglycinate, which has high bioavailability.
What does it mean for the formula to be ‘clean’ and free from synthetic additives?
Nutribiolite’s Iron Complex contains no colourings, artificial flavourings or added sugars. The excipients used – cassava starch and L-leucine – are of plant origin. This choice is in line with the principle of including only what is necessary for the product’s stability and ease of consumption, without ingredients that do not provide nutritional value.
This content is for information purposes only and is not a substitute for advice from a healthcare professional.
