Which iron supplement is less likely to cause constipation?

From the Guidelines

Ferrous gluconate and ferrous fumarate are less likely to cause constipation compared to ferrous sulfate, as they tend to be gentler on the digestive system. According to the study by 1, there is no substantial evidence that any one oral iron product is better than another in terms of effectiveness or tolerance. However, some patients may tolerate ferrous bisglycinate better, although there is no evidence of superiority in clinical trials. The study by 1 provides a comparison of oral iron preparations available in the UK, including ferrous sulfate, ferrous gluconate, and ferrous fumarate, and their respective elemental iron content and costs.

Some key points to consider when choosing an iron supplement to minimize constipation include:

• Taking a lower dose of iron (typically 65-100 mg of elemental iron daily) or splitting the dose throughout the day can reduce constipation risk 1
• Liquid iron formulations, such as iron drops or solutions, may also be better tolerated 1
• Slow-release or enteric-coated iron supplements might cause less gastrointestinal distress, though they may not be absorbed as effectively
• Taking iron supplements with vitamin C (like orange juice) enhances absorption, potentially allowing for lower doses 1
• Staying well-hydrated, consuming fiber-rich foods, and regular physical activity can help counteract constipation while taking iron

It's essential to note that the optimal drug, dosage, and timing of oral iron replacement therapy (IRT) for adults with iron deficiency anemia (IDA) are not clearly defined, and the effect of alternate day therapy on compliance and ultimate haematological response are unclear 1. However, a once daily dose of 50–100 mg of elemental iron taken in the fasting state may be the best compromise option for initial treatment. Regular Hb monitoring is recommended to ensure an ultimately satisfactory response.

From the FDA Drug Label

Unique, Innovative Iron Supplementation System• Enhanced GI Tolerability The FDA drug label does not answer the question.

From the Research

Iron Supplements and Constipation

• The study 2 compared the safety and efficacy of oral ferric citrate and placebo in patients with nondialysis-dependent CKD and iron deficiency anemia, and found that gastrointestinal disorders were the most common adverse events, with constipation reported in 18.8% of patients treated with ferric citrate and 12.9% of patients treated with placebo.
• The study 3 compared the therapeutic and side effects of ferrous and ferric in iron deficiency anemia, and found that literature review showed that the risk for gastrointestinal problems with ferrous is higher than that with ferric.
• The study 4 compared a combination ferrous fumarate product and a polysaccharide iron complex as oral treatments of iron deficiency anemia, and found that ferrous products are effective, but they are associated with more gastrointestinal side effects than ferric products.

Comparison of Iron Supplements

• The study 3 found that blood test values improved after iron deficiency anemia female patients who displayed poor therapeutic effects with oral ferric switched to ferrous.
• The study 4 found that the ferrous product was significantly more effective, but there was a slightly higher frequency of gastrointestinal side effects in patients taking the ferrous product.
• The study 5 compared the iron bioavailability of ferrous sulphate tablets with alternative commercial iron products, and found that naturally iron-rich mineral waters and synthetic liquid iron formulations have equivalent or better bioavailability compared with ferrous iron sulphate tablets.

Ferric vs Ferrous Supplements

• The study 2 found that ferric citrate was a safe and efficacious treatment for iron deficiency anemia, with constipation reported in 18.8% of patients.
• The study 3 found that ferrous supplements may be more effective than ferric supplements, but may also have a higher risk of gastrointestinal problems.
• The study 4 found that ferrous products are effective, but they are associated with more gastrointestinal side effects than ferric products.