The 40 mg dose of elemental iron is relatively high and approaches the safe upper limit for adults, which according to NIH data is around 45 mg per day (NIH ODS, 2025). Within clinical studies, doses in this range (approximately 40–120 mg/day) are indeed used to treat confirmed iron deficiency (Ebea-Ugwuanyi et al., 2024), but they are not meant for unlimited general maintenance in people without an increased need. If you do not have confirmed low ferritin or another clear indication, we recommend checking this with a doctor before long-term daily use of this dose, also because prolonged unnecessary iron supplementation can lead to its accumulation in the body.

Vitamin C (ascorbic acid) helps convert non-heme iron into a form that is more easily absorbed by the intestine, so the addition of vitamin C actually improves the utilization of the ingested iron (Cook, Reddy, 2001). This is especially useful for non-heme iron from supplements, such as the bisglycinate in this product, since it increases the effectively absorbed amount without needing to raise the iron dose itself. This is one of the few additions where this specific combination (iron + vitamin C) has solid scientific backing, unlike some other commonly added plant extracts in similar products.

Vegetarians and vegans, due to the absence of heme iron in their diet (which is absorbed more easily than non-heme iron from plant foods), often have a greater risk of lower iron intake and status, which is why they are mentioned as one of the target groups for this product. Nevertheless, 40 mg is a relatively high dose, so we recommend checking your iron status (ferritin) with a doctor or chosen laboratory before regular use, rather than deciding based solely on dietary habits. If it's only a mildly lower intake without confirmed deficiency, a lower-dose product such as Iron (20 mg) may be more suitable.

Clinical comparisons show that bisglycinate, at an equal or even lower dose of elemental iron, achieves a comparable increase in ferritin and hemoglobin as sulfate, while causing significantly fewer common side effects such as nausea, constipation and abdominal pain (Milman et al., 2014; Bumrungpert et al., 2022). This is especially important at higher doses, such as 40 mg, since digestive side effects with sulfate or fumarate typically increase with higher doses. Sulfate and fumarate are, however, well-established and cheaper forms with reliable effectiveness, but at a comparable dose they have poorer tolerability, which can reduce compliance with long-term use.