Does Optimal Iron Absorption Include Vitamin C?

Douglas S. Paauw, MD

July 15, 2021

A 46-year-old woman presents with fatigue. She reports that she has had unusually heavy periods for the past 6 months. Her blood work shows a hematocrit level of 32, a mean corpuscular volume of 77, a platelet count of 390,000, and a ferritin level of 5.

Dr Douglas Paauw

What would you recommend for iron replacement?

A. FeSO4 325 mg three times a day with vitamin C

B. FeSO4 325 mg daily with vitamin C

C. FeSO4 325 mg every other day

Recommendations and Supporting Research

I think I would start with choice C, FeSO4 every other day.

Treatment of iron deficiency with oral iron has traditionally been done by giving 150-200 mg of elemental iron (which is equal to three 325 mg tablets of iron sulfate).1 This dosing regimen has considerable gastrointestinal side effects. Recent evidence has shown that iron absorption is diminished the more frequently it is given.

Stoffel and colleagues found that fractional iron absorption was higher in iron-deficient women who were given iron every other day, compared with those who received daily iron.2 They also found that the more frequently iron was administered, the higher the hepcidin levels were, and the lower the iron absorption.

Karacok and colleagues studied every other day iron versus daily iron for the treatment of iron-deficiency anemia of pregnancy.3 A total of 217 women completed randomization and participated in the study, with all women receiving 100 mg of elemental iron, either daily (111) or every other day (106). There was no significant difference in increase in ferritin levels, or hemoglobin increase between the groups. The daily iron group had more gastrointestinal symptoms (41.4%) than the every other day iron group (15.1%) (P < .0057).

Düzen Oflas and colleagues looked at the same question in nonpregnant women with iron deficiency anemia.4 Study patients either received 80 mg iron sulfate twice a day, 80 mg once a day, or 80 mg every other day. There was no statistically significant difference in hemoglobin improvement between groups, but the group that received twice a day dosing of iron had statistically significantly higher ferritin levels than the daily or every other day iron groups. This improvement in ferritin levels came at a cost, though, as 68% of patients in the twice daily iron group had gastrointestinal symptoms, compared with only 10% in the every other day iron group (P < .01).

Vitamin C is often recommended to be taken with iron to promote absorption. The evidence for this practice is scant, and dates back almost 50 years.5,6

Cook and Reddy found there was no significant difference in mean iron absorption among the three dietary periods studied in 12 patients despite a range of mean daily intakes of dietary vitamin C of 51-247 mg/d.7

Hunt and colleagues studied 25 non pregnant, healthy women with low ferritin levels.8 The women’s meals were supplemented with vitamin C (500 mg, three times a day) for 5 of the 10 weeks, in a double-blind, crossover design. Vitamin C supplementation did not lead to a difference in iron absorption, lab indices of iron deficiency, or the biological half-life of iron.

Li and colleagues looked at the effect of vitamin C supplementation on iron levels in women with iron deficiency anemia.9 A total of 440 women were recruited, with 432 completing the trial. Women were randomized to receive iron supplements plus vitamin C or iron supplements only. Their findings were that oral iron supplements alone were equivalent to oral iron supplements plus vitamin C in improving hemoglobin recovery and iron absorption.

Bottom Line

Less frequent administration of iron supplements (every other day) is as effective as more frequent administration, with less GI symptoms. Also, adding vitamin C does not appear to improve absorption of iron supplements.

Douglas Paauw, MD, is professor of medicine in the division of general internal medicine at the University of Washington, Seattle, and he serves as third-year medical student clerkship director at the University of Washington. He is a member of the editorial advisory board of Internal Medicine News. He has no conflicts to disclose. Contact him at


1. Fairbanks VF and Beutler E. Iron deficiency, in “Williams Textbook of Hematology, 6th ed.” (New York: McGraw-Hill, 2001).

2. Stoffel N et al. Lancet Haematology. 2017;4: e524-33.

3. Karakoc G et al. J Matern Fetal Neonatal Med. 2021 Apr 18:1-5

4. Düzen Oflas N et al. Intern Med J. 2020 Jul;50(7):854-8

5. Cook JD and Monsen ER. Am J Clin Nutr. 1977;30:235-41.

6. Hallberg L etal. Hum Nutr Appl Nutr. 1986;40: 97-113.

7. Cook JD and Reddy M. Am J Clin Nutr. 2001;73:93-8.

8. Hunt JR et al. Am J Clin Nutr. 1994 Jun;59(6):1381-5.

9. Li N et al. JAMA Netw Open. 2020 Nov 2;3(11):e2023644.

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