Jern
Also known as: Jern, dietary iron, ferrous sulfate, ferric iron, Fe, Iron
Overview
Iron is an essential trace mineral (chemical symbol Fe, atomic number 26) critical for numerous bodily functions, primarily oxygen transport and various metabolic processes. It is naturally found in foods like red meat, poultry, fish, legumes, fortified cereals, and leafy green vegetables. Iron supplementation is predominantly used to prevent and treat iron deficiency anemia (IDA), enhance oxygen transport, and support cognitive and physical performance in individuals with deficiencies. Dietary iron exists in two forms: heme (from animal sources, higher bioavailability) and non-heme (from plant sources). Common supplement forms include ferrous sulfate, ferrous gluconate, and ferric salts. Research on iron supplementation is extensive, with a high maturity level and robust evidence from numerous randomized controlled trials, meta-analyses, and systematic reviews supporting its efficacy and safety for IDA and related conditions.
Benefits
Iron supplementation significantly improves hemoglobin levels and iron status markers (serum ferritin, transferrin saturation) in individuals with iron deficiency anemia (IDA), with typical hemoglobin increases of 1-2 g/dL over 4-12 weeks. Meta-analyses consistently demonstrate that iron reduces anemia prevalence and improves fatigue and cognitive function in deficient populations. There is also evidence suggesting that iron supplementation may enhance physical performance and immune function in iron-deficient individuals. Pregnant women, infants, children, menstruating women, and the elderly are populations that benefit most from iron supplementation to prevent or treat IDA. Effect sizes for hemoglobin improvement are moderate to large (standardized mean differences often >0.5), and reductions in anemia risk are substantial (relative risk reductions >30%). Hemoglobin improvements are typically observed within 4 weeks, with full correction of anemia usually achieved in 8-12 weeks.
How it works
Iron is a vital component of hemoglobin, the protein in red blood cells responsible for facilitating oxygen transport throughout the body. It also plays a crucial role in myoglobin function, which stores oxygen in muscles, and is essential for mitochondrial electron transport, a key process in cellular energy production. Furthermore, iron is a cofactor for numerous enzymatic reactions. Iron absorption primarily occurs in the duodenum and upper jejunum of the small intestine, a process tightly regulated by the hormone hepcidin. Once absorbed, iron is stored in ferritin and transported throughout the body by transferrin. Heme iron, found in animal products, has a higher bioavailability (15-35%) compared to non-heme iron from plant sources (2-20%). Vitamin C enhances the absorption of non-heme iron, while substances like phytates and polyphenols can inhibit it.
Side effects
Iron supplementation is generally safe when administered at appropriate dosages, but excess iron can lead to toxicity. Common side effects, affecting more than 5% of users, include gastrointestinal discomfort, constipation, nausea, and dark stools. Less common side effects (1-5%) may include diarrhea, vomiting, and abdominal pain. Rare side effects (less than 1%) can involve iron overload, particularly in individuals with conditions like hemochromatosis, and allergic reactions. Iron can interact with certain medications; its absorption can be reduced by antacids, calcium supplements, and tetracycline antibiotics. Conversely, iron can reduce the absorption of levothyroxine and some antibiotics. Iron supplementation is contraindicated in individuals with hemochromatosis, hemosiderosis, or anemias not caused by iron deficiency. Caution is advised for infants and the elderly, and dosage adjustments are often necessary during pregnancy.
Dosage
For the treatment of iron deficiency anemia (IDA), a typical minimum effective dose is 60-120 mg of elemental iron daily. The optimal dosage range for adults with IDA is generally 100-200 mg of elemental iron daily, often administered in divided doses. Doses exceeding 200 mg of elemental iron daily typically increase side effects without providing additional therapeutic benefit, and acute overdose can be toxic. For best absorption, iron supplements should ideally be taken on an empty stomach. However, to mitigate gastrointestinal side effects, they can be taken with food. Co-administration with vitamin C is recommended as it enhances non-heme iron absorption. Common forms include ferrous sulfate, ferrous gluconate, and ferrous fumarate, with ferrous sulfate being the most extensively studied. To optimize absorption, avoid concurrent intake with calcium, coffee, or tea. Vitamin C is a key cofactor for absorption, while copper and vitamin B12 are important for erythropoiesis.
FAQs
Is iron supplementation safe for everyone?
No, it is contraindicated in individuals with iron overload disorders like hemochromatosis and should always be used under medical supervision to ensure appropriate dosage and necessity.
How long does it take to see results from iron supplementation?
Improvements in hemoglobin levels are typically observed within 4 weeks of starting supplementation, with full correction of anemia usually achieved within 8-12 weeks, depending on the severity of the deficiency.
Can iron supplements cause constipation?
Yes, constipation is a common side effect of iron supplementation. Increasing dietary fiber intake and ensuring adequate hydration can help manage this symptom.
Should iron be taken with food?
For optimal absorption, iron is best taken on an empty stomach. However, if gastrointestinal side effects occur, taking it with a small amount of food can help reduce discomfort, though absorption may be slightly decreased.
Is iron supplementation effective for fatigue without anemia?
Evidence is mixed regarding the effectiveness of iron supplementation for fatigue in individuals who are not anemic. Benefits are primarily observed in those with diagnosed iron deficiency.
Research Sources
- https://academic.oup.com/pmj/article/98/1158/285/6958842 – This article discusses the importance of iron in human health, particularly its role in oxygen transport and energy metabolism. It highlights the global prevalence of iron deficiency and the clinical implications of inadequate iron intake, emphasizing the need for effective strategies to prevent and treat iron deficiency anemia.
- https://pmc.ncbi.nlm.nih.gov/articles/PMC10940388/ – This research provides an overview of iron metabolism and the pathophysiology of iron deficiency anemia. It details diagnostic approaches and various treatment options, including oral iron supplementation, discussing different formulations and their efficacy and side effect profiles.
- https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1567438/full – This study investigates the impact of iron supplementation on specific populations, such as athletes or pregnant women, focusing on its effects on performance, cognitive function, and overall health outcomes. It also explores novel approaches to iron delivery and absorption enhancement.
- https://www.nature.com/articles/s41430-019-0417-x – This article reviews the latest advancements in understanding iron homeostasis and the genetic factors influencing iron metabolism. It discusses the implications of iron dysregulation in various diseases, including both iron deficiency and iron overload conditions, and potential therapeutic targets.
- https://pubmed.ncbi.nlm.nih.gov/32805754/ – This publication summarizes the current evidence on the efficacy and safety of different iron supplement formulations. It provides practical recommendations for clinicians on dosing, monitoring, and managing side effects associated with oral iron therapy for iron deficiency anemia.
