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Iron Nutrition Summary for Dietitians

nutrition topics Nov 19, 2021

Written by Tracey Frimpong, RD, @thatblackrd 

Medically Reviewed by Olivia Farrow, RD, MHSc

 

This article will summarize all of the must-know information about iron nutrition for registered dietitians.

 

Dietitian Success Center’s membership includes access to vitamin & mineral supplement guides, a comprehensive yet simplified reference for finding the best supplements for your clients. You can quickly find the best iron supplement for anemia without constipation or a great plant-based iron supplement in DSC’s iron supplement reference chart. Become a member of DSC today to get your iron supplementation reference guide.

Iron is a key mineral found naturally in many foods, fortified in food products and can be taken as a supplement. 

 

Iron Nutrition Basics

Our red blood cells contain an important protein called hemoglobin. Hemoglobin is a complex made up of hemo (iron) and globin (protein). This protein helps to transfer oxygen from the lungs to the tissues around the body (1).

Iron is also involved in: 

  • The electron transport chain
  • Immune function
  • Cellular function
  • Hormone synthesis
  • Physical growth
  • Neurological development

Although most iron is found in hemoglobin, it can also be stored as ferritin or hemosiderin, which is found in the bone marrow, liver and spleen. 

Transferrin is the main protein found in blood that binds to iron to transport it around the body. 

Transferrin saturation determines the rate of iron uptake.

Many people, more specifically adolescents, premenopausal women, and the elderly, are at risk of developing iron deficiency due to increased requirements and insufficient intake. 

Both fortified foods and iron supplementation can be used to help meet daily recommendations (1).

 

What Causes Iron-Deficiency Anemia? 

The main factors that can cause iron deficiency anemia include (2):

  • Inadequate intake
  • Poor absorption
  • Increased losses 
  • And/or increased physiological demands for iron

Iron is lost in small amounts through feces, urine, the gastrointestinal system, and skin turnover. 

For menstruating women, losses are greater because of menses. 

High doses of aspirin, gastritis, parasites, and infections from Helicobacter pylori (which may cause ulcers) may result in other blood losses from the gastrointestinal system. 

Lastly, bariatric patients should be screened for iron deficiency because of GI manipulation (1).

 

Who is At Risk of Deficiency?

Left untreated, iron deficiency can turn into iron deficiency anemia (IDA). 

Those at risk include (but are not limited to):

  • Infants & Toddlers (premature or low-birth weight)
  • Pregnant women and teens
  • Menstruating women with heavy periods
  • School-aged children
  • People with cancer, gastrointestinal (GI) disorders, or heart failure
  • Professional athletes; more specifically females (5).  
  • Vegetarians
  • Given that iron from plant-based food is not absorbed as readily in the body, vegetarians require 1.8 times the daily recommended amount of iron compared to non-vegetarians. Vegan iron supplements may be necessary in some cases. 

 

How is Iron Deficiency Diagnosed?

(8, 9, 10)

Iron deficiency progresses to full onset iron deficiency anemia depending on the various iron stores and can be categorized as: 

  •  Mild iron deficiency - which occurs when there is a depletion of iron stores.
  • Iron deficiency erythropoiesis - which occurs when iron stores are depleted, transferrin saturation declines, but hemoglobin remains in a normal range (11). 
  • Iron deficiency anemia (IDA) - which occurs when hemoglobin is low, and mean corpuscular volume (erythrocyte size) and hematocrit (red blood cells: blood volume ratio) has decreased. 

 

Signs & Symptoms of Iron Deficiency (12)

  • Growth restriction
  • Impaired physical endurance
  • Impaired neurodevelopment
  • Fatigue
  • Shortness of breath
  • Dizziness
  • Cold extremities
  • Heart murmur
  • Heart failure
  • Brittle nails
  • Swelling and soreness
  • Cracks on sides of the mouth
  • Enlarged spleen
  • Pica – eating non-food materials such as chalk, clay, and dirt
  • Restless leg syndrome (RLS)
  • Thinning of hair around forehead
  • Pagophagia - chewing of ice

 

Food Sources of Iron 

There are two main forms of iron found in foods: heme (ferrous/Fe2 +) and non-heme (ferric/Fe3+) iron. Absorption depends on the form of iron being consumed.

Heme iron - found in animal products such as meat, poultry, and seafood and can be easily absorbed by the body. 

Non-heme iron - found in plants and iron-fortified foods, like legumes, eggs, tofu, whole grains, vegetables, fruits, and iron-fortified products such as cereals and plant-based beverages. Non-heme iron is not readily absorbed by the body. 

Vegetables (non-heme)

  • Spinach, cooked: 2-3.4 mg Iron per ½ cup
  • Tomato puree: 2.4 mg Iron per ½ cup
  • Edamame, cooked: 1.9-2.4 mg iron per ½ cup
  • Lima beans, cooked: 2.2 mg per ½ cup 
  • Raw asparagus: 2.1 mg iron per 6 spears
  • Cooked potato with skin: 1.3-1.9 mg iron per 1 medium 
  • Turnip, cooked: 1.5 – 1.7 mg iron per ½ cup
  • Kale., cooked: 1.3 mg iron per ½ cup
  • Tomato sauce: 1.2 mg iron per ½ cup

Grains (non-heme)

  • Cooked oatmeal: 4.5-6.6 mg iron per ¾ cup
  • Cooked teff: 3.88 mg iron per ¾ cup
  • Cream of wheat, cooked: 5.7-5.8 mg iron per ¾ cup 
  • Cereal, dry: 4.0-4.3 mg iron per 30 g
  • Granola bar: 1.2-2.7 mg iron per 1 bar
  • Soda crackers: 1.5-2.3 mg iron per 6 crackers
  • Oat bran cereal, cooked: 2.0 mg iron per ¾ cup
  • Pasta, cooked: 1.2 mg iron per ½ cup 
  • Sorghum flour: 2.85 mg iron per ¾ cup

Milk & Alternatives (non-heme)

  • Soy yogurt: 2.1 mg iron per ¾ cup 

Beans (non-heme)

  • Tofu: 2.4-8 mg iron per ¾ cup
  • 2 cooked eggs: 1.2-1.8 mg iron
  • Hummus: 1.5 mg iron per ¼ cup

Nuts (non-heme)

  • Almond Butter: 1.1 mg iron per 2 tablespoons 
  • Pumpkin seeds: 2.85 mg iron per ¼ cup

Meats (heme)

  • Pork liver: 13.4 mg iron per 65 g/2.5 oz
  • Poultry liver: 6.2-9.7 mg per iron 75 g/2.5 oz 
  • Lamb kidney: 9.3 mg iron per 75 g/2.5 oz 
  • Duck: 1.8-7.4 mg iron per 75 g/2.5 oz
  • Beef liver: 4.9 mg iron per 75 g/2.5 oz 
  • Moose: 2.5-3.8 mg iron per 75 g/2.5 oz
  • Beef: 1.4-3.3 mg iron per 75 g/2.5 oz
  • Ground meat: 1.3-2.1 mg iron per 75 g/2.5 oz
  • Lamb: 1.3-2.1 mg iron per 75 g/2.5 oz
  • Chicken: 0.4-2.0 mg iron per 75 g/2.5 oz
  • Pork: 0.5-1.5 mg iron per 75g/20z
  • Ground poultry: 0.7-0.8 mg iron per 75g/20 oz
  • Turkey: 0.3-0.8 mg iron per 75 g/2.5 oz

Seafood (heme)

  • Crab: 0.6-2.2 mg iron per 75 g/2.5 oz
  • Canned sardines: 1.7-2.2 mg iron per 75 g/2.5 oz
  • Canned tuna in water: 1.2 mg iron per 75 g/2.5 oz

(1, 13, 14)

 

Dietary Factors That Influence Absorption

Iron is readily absorbed in the duodenum and upper jejunum. Understanding the dietary factors that influence iron absorption can help when supporting clients on how to take iron supplements for best absorption.

Absorption is reduced by:

  • Fibre
    • Different sources of fibre are capable of decreasing the bioavailability of iron sources (16).
  • Phytates (Phytic acid)
    • Almonds, Brazil nuts, raw sesame seeds, wheat bran, raw oats, All Bran cereal, raw wild rice, raw kidney beans, raw pinto beans, and soybean meal 
    • Phytate is a phosphorus-containing compound found in the outer husks of cereal grains. Phytates are found commonly in grains, vegetables, nuts, seeds, and soy. 
    • Examples of foods with high phytic acid include: 
  • Tannins
    • Naturally found in tea compounds which bind with non-heme iron more specifically. 
  • Oxalate (Oxalic acid)
    • Green gooseberries, citrus peels, rhubarb, tangerines, amaranth (beans in tomato sauce), beets, cassava root, swiss chard, collards, leek, okra, parsley, purslane, spinach (boiled/frozen), almonds, peanuts, pecans, wheat germ, poppy seeds, peanut butter, chocolate, dry cocoa, fig newton, soybean crackers, sunflower seeds, and pepper
    • Per 100 g (1/2 cup) all have > 70 mg of oxalic acid
  • Calcium/Dairy

Absorption is increased by:

  • Vitamin C (ascorbic acid, enhances the bioavailability of non-heme iron) (1)
  • Meat Factor - a special factor found in meat, poultry and fish that enhances the absorption of iron

(15)

 

Iron Supplementation 

Iron supplementation may be indicated for those who can’t meet their dietary needs from food alone. 

Most women’s multivitamins/mineral supplements contain approximately 18 mg of iron (100% of the RDA). Multivitamins for men and seniors typically contain very little or no iron as their requirements different. There are iron-only supplements which provide more than the daily requirements and can reach very high doses. 

When suggesting supplements, it is important that individuals are monitored for compliance and tolerance. Understanding how to take iron supplements for best absorption is also important. 

DSC’s iron supplement guide includes a thorough iron supplement reference chart with the different types of iron supplements available with an overview the benefits and disadvantages of each. Brand examples and cost comparisons are also included in the iron supplement reference chart for dietitians.

 

Other ways to increase dietary iron

  1. Canada’s Lucky Fish/Leaf Iron (23)
    • Made in Canada, it is a reusable cooking tool that naturally helps to add extra iron in daily food or drinks. Using the Lucky Iron Fish/Leaf 3 times a week for 3-12 months can help increase iron stores. 
  2. Cast-iron pots and pans

Medical Directives

Ensure that you are aware of medical directives on supplementation in your jurisdiction. In some cases, Registered Dietitians are able to suggest iron supplements up to a certain dose (30 mg), anything above this amount is considered a schedule II drug and requires a medical directive signed by a physician. To retrieve labs and monitor the efficacy of iron supplementation and maintenance it requires a medical directive also signed by the physician. 

* Medical directives differ between different practice settings, so ensure that you consult with requirements in your location. 

(24)

 

How to Take Iron Supplements for Best Absorption

Evidence indicates that providing a single daily dose of iron is better tolerated daily and even when alternating iron every other day. It can potentially provide better serum ferritin concentrations in patients rather than providing half-dosages on alternate days (25, 26). Requirements differ from person-to-person. 

Iron is better absorbed on an empty stomach; however, it is better tolerated on a full stomach. Iron taken on an empty stomach can cause intense nausea, which may reduce patient compliance.

A common side effect of iron supplementation is constipation. A typical iron intervention lasts for two months, so long-term constipation can be challenging for patients/clients. Remedies for constipation such as flaxseeds, soluble fibre, and prune juice can help to ease the symptoms. It can also help to know the best iron supplement for anemia without constipation which you can find in the DSC iron supplement guide. 

Other side effects due to oral iron supplements include (1, 2):

  • Dental stains (liquid iron)
  • Nausea/vomiting
  • Dyspepsia
  • Bloating
  • Constipation
  • Diarrhea
  • Dark (black) stools

 

Safety and Contraindications

Interactions with medications:

Iron supplements can interact with other medications, therefore healthcare professionals should screen for these potential interactions. Individuals who are taking carbonate acids, calcium, phosphorus, zinc, and/or copper supplements should take their iron 2 hours pre/post these medications (15)

Other potential interactions: proton pump inhibitors, H2 blockers, tetracyclines, levodopa, levothyroxine, and laxatives. 

Contraindications: (27)

Patients with iron-overloaded states such as hereditary hemochromatosis, hemosiderosis, or with a history of hemolytic anemia should not take iron supplements. 

 

Take-home messages for dietitians: 

  • Risk factors for iron deficiency anemia include: inadequate intake, poor absorption, increased losses and/or increased physiological demands for iron
  • Those at risk include infants and toddlers, pregnant women and teens, menstruating women with heavy periods, school-aged children, individuals with cancer, GI disorders or heart failure, athletes and vegans/vegetarians
  • Heme iron is found in animal products and is better absorbed by the body than non-heme iron, which is found in plant-based foods. 
  • Iron deficiency is diagnosed by measuring serum ferritin concentration in addition to mean corpuscular volume and/or hemoglobin.
  • Deficiency can range from mild iron deficiency to iron deficiency anemia. 
  • Restoring iron stores can be achieved through increasing iron in the body, supplementation, using a Lucky Iron Fish or cast iron cookware. 

At DSC, we make it easier for dietitians and dietetic students to build expertise in topics including iron supplements. Our vitamin and mineral supplement guides, nutrition courses, ready-to-use client handouts, and community can help you feel more confident. 

Dietitian Success Center is THE professional development resource for dietitians and dietetic students. Our mission is to make it easier for dietitians and dietetic students to build expertise. We do this through evidence-based online nutrition courses, community, and ready-to-use client handouts. Plus - we give you the tools to start and grow your dietitian private practice! 

 

References: 

  1. Centers for Disease Control and Prevention. Iron deficiency – United States, 1999-2000. Morbidity and Mortality Weekly Report. 2002;51:897–899.
  2. Dietitians of Canada. Hematology/haematology – anemia/anaemia – iron deficiency background. In: Practice-based evidence in nutrition. [PEN]. 2016; [Cited: Nov 06 2017]. Available from: https://www.pennnutrition.com/KnowledgePathway.aspx?kpid=403&trid+22667&trcatid=38 Access only by subscription.
  3. Canada, H. (2006, June 29). Government of Canada. Canada.ca. https://www.canada.ca/en/health-canada/services/food-nutrition/healthy-eating/dietary-reference-intakes/tables/reference-values-elements-dietary-reference-intakes-tables-2005.html.
  4. National Academies of Sciences. (2019, March 5). Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes, Elements, Food and Nutrition Board, National Academies - Dietary Reference Intakes for Sodium and Potassium - NCBI Bookshelf. National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/books/NBK545442/table/appJ_tab3/?report=objectonly.
  5. Deldicque L, Francaux M. Recommendations for healthy nutrition in female endurance runners: an update. Front Nutr. 2015;2:17.
  6. Breymann C, Auerbach M. Iron deficiency in gynecology and obstetrics: clinical implications and management. Hematology Am Soc Hematol Educ Program. 2017;2017(1):152-159. doi:10.1182/asheducation-2017.1.152
  7. PocketPills. (2020). Birth Control Pills and Iron Deficiency. PocketPills. https://www.pocketpills.com/blog/birth-control/birth-control-pills-and-iron-deficiency. 
  8. Auerbach M. How we diagnose and treat iron deficiency anemia. Am J Hematol 2016;91:31- 38.
  9. Thomas D, Hinchliffe R, Briggs C, Macdougall I, Littlewood T, Cavill I, et al. Guideline for the laboratory diagnosis of functional iron deficiency. Br J Haematol. 2013 Jun;161(5):639-48.
  10.   Herbert, V., Jayatilleke, E., Shaw, S., Rosman, A. S., Giardina, P., Grady, R. W., ... & Gunter, E. W. (1997). Serum ferritin iron, a new test, measures human body iron stores unconfounded by inflammation. Stem cells, 15(4), 291-296. 
  11.  Brugnara C. (2003). Iron deficiency and erythropoiesis: new diagnostic approaches. Clinical chemistry, 49(10), 1573–1578. https://doi.org/10.1373/49.10.1573
  12.  Akman M et al. The effects of iron deficiency on infants’ developmental test performance. Acta Paediatrica. 2004;Oct;93(10):1391–1396.
  13. Health Canada. Canadian Nutrient File, version 2015 https://food-nutrition.canada.ca/cnf-fce/index-eng.jsp
  14. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. fdc.nal.usda.gov.
  15. Pronsky, Z. M., & Crowe, J. P. (2010). Food medication interactions (16th ed.). Food-Medication Interactions.
  16. Adams, Seidu & Sello, Cornelius & Qin, Gui-Xin & Che, Dongsheng & Han, Rui. (2018). Does Dietary Fiber Affect the Levels of Nutritional Components after Feed Formulation?. Fibers. 6. 10.3390/fib6020029.
  17. Murray-Kolbe LE, Beard J. Iron. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:432-8.
  18. 1 Anemia Guidelines for Family Medicine (Toronto: MUMS Guidelines, 2014); 8.2 Klein-Schwartz W: Toxicity of polysaccharide-iron complex exposures reported to poison control centers. The Annals of Pharmacology 2000, February, Vol. 34; 165.
  19. British Columbia Ministry of Health. BC HealthFiles: Iron and Your Health. Available at http://www.healthlinkbc.ca/healthfiles/pdf/hfile68c.pdf. Accessed December 3, 2008.
  20. Hallberg L, Hulthen L. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron.  American Journal of Clinical Nutrition. 2000;71:1147-1160.
  21. Seligman PA et al. Clinical studies of HIP: an oral heme-iron product.  Nutrition Research. 2000;20(9):1279-1286.
  22. BC Children's Hospital. (2018). Iron Deficiency Anemia. BC Children's Hospital. http://www.bcchildrens.ca/Oncology-Site/Documents/Hem%20Iron%20deficiency.pdf.
  23. Armstrong, G. (2016).  Commercializing the Lucky Iron Fish™ using Social Enterprise: a novel health innovation for iron deficiency and anemia in Cambodia and beyond (Doctoral dissertation).
  24. Cohen, D. (2016). Update on Vitamins and Minerals & the RD Scope of Practice. College of Dietitians of Ontario. Retrieved from https://www.collegeofdietitians.org/resources/scope-of-practice/vitamins-and-minerals/update-on-vitamins-and-minerals-and-the-rd-scope-o.aspx
  25. Stoffel, N. U., Cercamondi, C. I., Brittenham, G., Zeder, C., Geurts-Moespot, A. J., Swinkels, D. W., ... & Zimmermann, M. B. (2017). Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials.  The Lancet Haematology, 4(11), e524-e533.
  26. Moretti, D., Goede, J. S., Zeder, C., Jiskra, M., Chatzinakou, V., Tjalsma, H., Melse-Boonstra, A., Brittenham, G., Swinkels, D. W., & Zimmermann, M. B. (2015). Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood, 126(17), 1981–1989. https://doi.org/10.1182/blood-2015-05-642223
  27. Nguyen M, Tadi P. Iron Supplementation. [Updated 2021 Jan 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557376/

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