Iron and Increased Hemoglobin Levels

Research synthesisModerate evidenceSmall effect5 studies · 4 beneficial · 1 neutral · 0 harmful

Across all 5 studies, 4 reported beneficial effects of iron supplementation on hemoglobin levels, with 4 reaching statistical significance. Effects were consistently small in magnitude. The median study duration was 58 days, and the most studied population was non-anaemic iron-deficient women of reproductive age. One meta-analysis in healthy blood donors used elemental iron at 7–105 mg/day.

Effective dose range: 7–105 mg/day elemental iron (based on one meta-analysis); other studies reported doses as 4.4–55 mg/day or 0.2–112.8 mg/100 g food, with no clear convergence.
Studied populations: non-anaemic iron-deficient women of reproductive age, healthy blood donors, general populations (including pregnant women) from any country

Caveats: Available evidence is overwhelmingly positive — clinical literature in this area is subject to publication bias (null-result studies are less likely to be published or indexed). Evidence certainty is moderate due to small sample sizes and very low-certainty evidence in some meta-analyses. One study on rice fortification showed neutral findings, and many studies involved fortification with multiple micronutrients, making it difficult to isolate the effect of iron alone.

Generated Jun 15, 2026

Doses used in studies

Elemental Iron · mg/day: 7–105 (median 56, IQR 7–105) — 1 study
mg/100g: 0.2–112.8 (median 56.5, IQR 0.2–112.8) — 1 study
mg/day: 4.4–55 (median 29.7, IQR 4.4–55) — 1 study

Time to effect

Median: 8.3 weeks · IQR 8.1 weeks–8.4 weeks · Range 8 weeks–8.6 weeks — Reported in 2 of 5 studies

Safety in these studies

abdominal painIncreased riskRR 1.69, 95% CI 1.15 to 2.47
More participants may experience adverse events with oral iron compared to no iron, including abdominal pain, constipation, and diarrhoea (RR 1.69, 95% CI 1.15 to 2.47; 8 studies, 2641 participants)
from: Oral or parenteral iron supplementation to reduce deferral, iron deficiency and/or anaemia
constipationIncreased riskRR 1.69, 95% CI 1.15 to 2.47
More participants may experience adverse events with oral iron compared to no iron, including abdominal pain, constipation, and diarrhoea (RR 1.69, 95% CI 1.15 to 2.47; 8 studies, 2641 participants)
from: Oral or parenteral iron supplementation to reduce deferral, iron deficiency and/or anaemia
diarrhoeaIncreased riskRR 1.69, 95% CI 1.15 to 2.47
More participants may experience adverse events with oral iron compared to no iron, including abdominal pain, constipation, and diarrhoea (RR 1.69, 95% CI 1.15 to 2.47; 8 studies, 2641 participants)
from: Oral or parenteral iron supplementation to reduce deferral, iron deficiency and/or anaemia
hookworm infectionIncreased riskRR 1.78, 95% CI 1.18 to 2.70; 785 participants
One study reported that fortification of rice with iron alone or with other micronutrients may slightly increase hookworm infection (RR 1.78, 95% CI 1.18 to 2.70; 785 participants; low-certainty evidence).
from: Fortification of rice with vitamins and minerals for addressing micronutrient malnutrition
Overall tolerabilityReported
No studies reported adverse effects.
from: Fortification of condiments and seasonings with iron for preventing anaemia and improving
diarrhoeaReportedRR 3.52, 95% CI 0.18 to 67.39; 1 study, 258 participants
We are uncertain about the effect of fortified rice on diarrhoea (RR 3.52, 95% CI 0.18 to 67.39; 1 study, 258 participants; very low-certainty evidence).
from: Fortification of rice with vitamins and minerals for addressing micronutrient malnutrition
weaknessReported
There may be no difference in reported non-gastrointestinal symptoms, except a feeling of 'weakness', which was reduced with oral iron supplements.
from: Oral or parenteral iron supplementation to reduce deferral, iron deficiency and/or anaemia

5 of 5 papersPopulation:

Effect of iron therapy on fatigue symptoms in non-anaemic iron deficient women of reproductive age- A Randomized Controlled Trial.
- 2026-01-01
- RCT · n = 164
- JPMA. The Journal of the Pakistan Medical Association 76(1)
- - Nayyer Sultana
  - Fariha Aslam Bajwa
  - Mirza Zeeshan Sikandar
  - Muhammad Mahtab Haider
  - Tayyaba Majeed
- PubMed: 41736325
- DOI: 10.47391/jpma.22068
3 Insights on
- Increased Hemoglobin Levels
- High evidence
- Large Human Trial
- Clinical
In Group 1, significant decrease in fatigue score and significant increase in ferritin and haemoglobin levels were noted post-intervention (p=0.05).
Effect
Beneficial
Effect size
Small
Significant
Yes
Oral or parenteral iron supplementation to reduce deferral, iron deficiency and/or anaemia in blood donors.
- 2026-06-04
- Meta-Analysis · n = 7,475
- The Cochrane database of systematic reviews 2026(6)
- - Louise J Geneen
  - Karyna Atha
  - Catherine Kimber
  - William McClune
  - Carolyn Dorée
  - Chiara Vendramin
  - Lian Wea Chia
  - David J Roberts
- PubMed: 42240175
- DOI: 10.1002/14651858.cd009532.pub3
3 Insights on
- Increased Hemoglobin Levels
- High evidence
- Adults
Hb and ferritin may also be improved with oral iron supplementation compared to no iron (Hb: mean difference (MD) 2.52, 95% CI 0.77 to 4.26 g/L higher; 14 studies, 1940 participants; ferritin: MD 12.39, 95% CI 8.16 to 16.62 ng/mL higher; 8 studies, 1335 participants), but the evidence is very uncertain.
Effect
Beneficial
Effect size
Small
Significant
Yes
Dose
variable (7 to 105 mg/day elemental iron)
Fortification of condiments and seasonings with iron for preventing anaemia and improving health.
- 2023-09-01
- Meta-Analysis · n = 4,459
- The Cochrane database of systematic reviews 2023(9)
- - Chowdhury Sb Jalal
  - Luz Maria De-Regil
  - Vanessa Pike
  - Prasanna Mithra
- PubMed: 37665781
- DOI: 10.1002/14651858.cd009604.pub2
4 Insights on
- Increased Hemoglobin Levels
- High evidence
- Clinical
We are uncertain about whether fortification of condiments/seasonings with iron plus other micronutrients will improve haemoglobin concentration (MD 6.22 g/dL, 95% CI 1.60 to 10.83; 1270 participants; 5 studies; very low-certainty evidence).
Effect
Beneficial
Effect size
Small
Significant
Yes
Dose
4.4–55 mg/day
Fortification of rice with vitamins and minerals for addressing micronutrient malnutrition.
- 2019-10-25
- Meta-Analysis · n = 8,245
- The Cochrane database of systematic reviews 2019(10)
- - Juan Pablo Peña-Rosas
  - Prasanna Mithra
  - Bhaskaran Unnikrishnan
  - Nithin Kumar
  - Luz Maria De-Regil
  - N Sreekumaran Nair
  - Maria N Garcia-Casal
  - Juan Antonio Solon
- PubMed: 31684687
- DOI: 10.1002/14651858.cd009902.pub2
8 Insights on
- Increased Hemoglobin Levels
- High evidence
- Mixed
Fortification of rice with vitamin A (in combination with other micronutrients) may increase mean haemoglobin (MD 10.00, 95% CI 8.79 to 11.21; 1 study, 74 participants; low-certainty evidence)
Effect
Neutral
Effect size
Small
Significant
No
Dose
as part of combined micronutrient fortification
Improved Iron Status, but Not Protein Source, Is Related to Appetite, Satiety, and Mood in Women of Reproductive Age With Iron Deficiency: A Randomized Controlled Trial.
- 2026-06
- RCT
- The Journal of nutrition 156(6)
- - Stephen R Hennigar
  - Katelyn M Miller
  - Robert D Murphy
  - Amy Braymer
  - Christy L Mayet
  - Frank L Greenway
  - Susan N Cheung
  - Camila Weschenfelder
  - Claire E Berryman
- PubMed: 42061720
- DOI: 10.1016/j.tjnut.2026.101559
10 Insights on
- Increased Hemoglobin Levels
- High evidence
- Clinical
changes in transferrin saturation (r = 0.4, P < 0.01) and hemoglobin (r = 0.3, P = 0.04) and hematocrit (r = 0.3, P = 0.03) were positively associated with changes in prospective food consumption
Effect
Beneficial
Effect size
Small
Significant
Yes
Dose
once a day for 8 weeks

Iron and Increased Hemoglobin Levels

Effect of iron therapy on fatigue symptoms in non-anaemic iron deficient women of reproductive age- A Randomized Controlled Trial.

Oral or parenteral iron supplementation to reduce deferral, iron deficiency and/or anaemia in blood donors.

Fortification of condiments and seasonings with iron for preventing anaemia and improving health.

Fortification of rice with vitamins and minerals for addressing micronutrient malnutrition.

Improved Iron Status, but Not Protein Source, Is Related to Appetite, Satiety, and Mood in Women of Reproductive Age With Iron Deficiency: A Randomized Controlled Trial.