Iron (ferrous sulfate vs bisglycinate vs other forms) and energy
What 5 graded rows on iron (ferrous sulfate vs bisglycinate vs other forms) agree on for energy, and where they differ. Counted side by side, never averaged.
Consensus finder Rows from the Iron (ferrous sulfate vs bisglycinate vs other forms) page, reviewed Oct 21, 2026 How it decides
What the rows agree on
Each block and row is one graded row from the Iron (ferrous sulfate vs bisglycinate vs other forms) page, with its PubMed record.
Your question
Iron (ferrous sulfate vs bisglycinate vs other forms) and energy
5 rows · 23,762 peopleSplit. 3 rows found an improvement, 1 found a worse outcome and 1 had mixed results.
- AGrade A× 2
- BGrade B× 1
- CGrade C× 1
- DGrade D× 1
- Rows
- 5
- Trials
- 5
- At least: a review without a trial count
- People
- 23,762
- Pooled reviews may count some twice
Where they differ
From the rowsThe best-graded row, grade A, is a meta-analysis of 6,861 people (2016) and found an improvement.
The 3 rows that found an improvement were larger: a median of 6,861 people, against 3,168 people for the row that found a worse outcome.
Only the 3 rows that found an improvement name women in their population.
The 3 rows that found an improvement are newer (2016 to 2024) than the row that found a worse outcome (2015).
1 row with mixed results is left out of this comparison.
The rows
3 improved · 1 worse · 1 mixed- AGrade AHemoglobin and iron status in menstruating women · Improved
Meta-analysis · n 6,861 · 2016 · 51 trials in menstruating women (67 trials, 8506 women overall)
Varied across trials · Varied across trials
Hemoglobin was 5.30 g/L higher with iron (high-quality evidence). Iron also lowered the risk of anaemia (RR 0.39; 3273 women) and iron deficiency (RR 0.62; 1088 women), moderate-quality evidence.
Row on the Iron (ferrous sulfate vs bisglycinate vs other forms) page · PubMed 27087396 (opens PubMed)
- BGrade BLow hemoglobin in pregnancy · Improved
Meta-analysis · n 13,543 · 2024 · 14 trials in pregnant women (57 trials, 48,971 women overall)
Varied across trials · During pregnancy
Daily iron may reduce maternal anaemia (4.0% vs 7.4%; RR 0.30), low-certainty evidence, and probably reduces iron-deficiency anaemia at term (RR 0.41), moderate certainty. Evidence on side effects was very uncertain.
Row on the Iron (ferrous sulfate vs bisglycinate vs other forms) page · PubMed 39145520 (opens PubMed)
- DGrade DIron absorption: alternate-day vs consecutive-day · Improved
RCT · n 40 · 2017 · Iron-depleted women aged 18-40 (serum ferritin ≤25 μg/L)
60 mg iron per morning, consecutive or alternate days · 14 days (consecutive) vs 28 days (alternate)
Cumulative fractional absorption was 21.8% on alternate days vs 16.3% on consecutive days, and total absorbed iron 175.3 vs 131.0 mg. In a second study (n=20), splitting 120 mg into two daily doses did not raise absorption.
Row on the Iron (ferrous sulfate vs bisglycinate vs other forms) page · PubMed 29032957 (opens PubMed)
- AGrade AStomach and bowel side effects with ferrous sulfate · Worse
Meta-analysis · n 3,168 · 2015 · 20 placebo-controlled trials in adults
Varied across trials · Varied across trials
Ferrous sulfate raised the odds of gastrointestinal side effects versus placebo (OR 2.32; 95% CI 1.74-3.08). Meta-regression found no clear link with the iron amount.
Row on the Iron (ferrous sulfate vs bisglycinate vs other forms) page · PubMed 25700159 (opens PubMed)
- CGrade CIron stores and side effects: alternate-day vs daily · Mixed
RCT · n 150 · 2023 · Young Swiss women with serum ferritin ≤30 μg/L
100 mg iron daily for 90 days vs on alternate days for 180 days (same total) · 6 months
Ferritin did not differ (43.8 vs 44.8 μg/L). Daily dosing had more gastrointestinal side effects on iron days (LPR 1.56), and iron deficiency at 6 months was 11.4% with daily vs 3.0% with alternate-day dosing.
Row on the Iron (ferrous sulfate vs bisglycinate vs other forms) page · PubMed 38021373 (opens PubMed)