Iron absorption and ferritin levels can be optimized by balancing dietary intake of heme and non-heme iron, using absorption enhancers like vitamin C, and avoiding inhibitors.

A Review on Ferritin

Ferritin is the primary storage molecule for iron in the body, housing any extra iron that is not immediately being used for cellular functions. Almost all of the ferritin in the body exists within the cells, however a small portion circulates in the blood (also referred to as serum ferritin) (1) and this is the value you receive as a result of ferritin testing. In addition to iron storage, ferritin keeps iron away from invading pathogens, acts as an iron transport molecule, and protects DNA, lipids and proteins in the body from oxidative stress that can be caused by free iron atoms (1).

Iron is unique from other trace minerals in that there is no direct pathway to excrete it from the body (2). Iron is reused and conserved in our system (2), thus iron homeostasis is mainly regulated through levels of absorption in the digestive tract (3). The form of iron-containing foods we eat, and what we choose to consume along with them, have a significant impact on iron absorbed into the body (2).

Dietary Iron

The Recommended Daily Allowance (RDA) of iron varies depending on age, sex, and at various developmental stages such as puberty and pregnancy. In adults (aged 19-50), the RDA of iron for men is 8mg and for women is 18mg due to the blood loss during menstruation. During pregnancy the RDA increases to 27mg to support the increased demand for iron in the rapidly growing fetus, but falls to 9mg during lactation (4). After the age of 50 the RDA shifts to 8mg for both men and women under the assumption that menopause removes the need for excess iron to supplement blood loss (4).

To see the RDA of iron over the entire lifespan, access the NIH Consumer Fact Sheet here.

Dietary iron comes in two forms; heme and non-heme iron. Heme iron is only found in animal products as the iron is bound to hemoglobin and myoglobin in the blood and muscle tissue. Non-heme iron is primarily found in plant products, but can also be found in meat as animals consume plants with non-heme iron (5).

• Foods high in heme iron:
• Red meat (Beef liver is one of the highest sources)
• Poultry
• Seafood (ie. oysters, sardines, tuna)

• Foods rich in non-heme iron:
• Legumes (ie. lentils, beans, soybeans/tofu/tempeh)
• Vegetables and Fruit (ie. spinach, tomatoes, kale, figs, raisins)
• Nuts & Seeds
• Grains (ie. oats, quinoa, millet)
• Fortified Foods (ie. cereals, wheat)

Factors Affecting Absorption

The amount of iron in each food does not equal the amount of iron that will be absorbed into the body. This is where bioavailability and nutrient-nutrient interactions become important to consider when optimizing dietary iron intake.

Bioavailability

Bioavailability refers to the proportion of a nutrient that is actually absorbed and utilized from digested foods in the intestine (3). Heme iron has a bioavailability between 15-35%, whereas non-heme iron only has a bioavailability between 2-20% (2). The volume of non-heme iron foods in most diets makes it the greatest contributor to total dietary iron intake over heme iron sources, with up to 90% of dietary iron coming from non-heme sources and around 10-15% coming from heme iron sources (2,3). However, due to the high bioavailability of heme iron, it can account for over 40% of the iron actually absorbed in the intestine (3).

Nutrient-Nutrient Interactions

Iron can exist in multiple chemical states in the body, and the state of iron when entering the intestine heavily impacts it’s absorption. Different nutrients consumed concurrently with iron can have either enhancing or inhibiting effects on iron absorption based on what chemical form iron takes when interacting with them (3).

These interactions primarily affect non-heme (plant-based) iron absorption, making dietary composition a more significant factor for those on vegan or vegetarian diets in the maintenance of a healthy iron status (3).

Enhancers of Iron Absorption:

Ascorbic Acid (Vitamin C):

Ascorbic acid is a strong enhancer of iron absorption, and has been shown to overcome the negative effects of some iron inhibitors such as phytates and polyphenols (2). Foods rich in vitamin C include citrus fruits, kiwi, red and green pepper, broccoli, strawberries, cantaloupe, baked potato, and tomatoes (6).

The Meat Factor:

Inhibitors of Iron Absorption:

• Phytates & Polyphenols: Both major inhibitors of iron absorption in plant-based diets as they create a complex with dietary iron and cannot be digested, making anything they are bound to not bioavailable (3).
• Phytates are found in in all grains, nuts, legumes and seeds (5). The amount consumed corresponds with the level of inhibition on iron absorption in the intestine (3).
• Polyphenols are found in vegetables, cereals, cocoa, spices, coffee, tea, and wine (3).

• Calcium: In contrast to the inhibitors listed above, calcium can impact both non-heme and heme iron absorption due to it’s proposed mechanism of affecting iron transport proteins within the intestine itself as opposed to changing the structure of iron (3).
• Calcium is mainly consumed via dairy products, but additional sources include dark leafy green vegetables and in fortified foods (7)
• Some Proteins: While meat proteins enhance iron absorption, the proteins that come from milk and eggs (casein, whey, and albumin) have been show to be inhibitors of iron absorption, and the protein in soybeans decreases iron absorption (2,3).

Dietary Strategies and Special Considerations

Increasing Ferritin Levels

If your goal is to increase stored iron (ferritin) in the body, pairing enhancers of iron absorption with foods high in iron is one strategy to use.

➤ Try this: Mediterranean Grain Bowl

Build a base with quinoa and lentils, include produce such as spinach, diced bell peppers, and tomato, and finish with a Greek dressing and protein source such as chicken.

Here, the non-heme iron sources (quinoa, lentils, and spinach) will have increased absorption from the vitamin C present in the peppers and tomato. The meat will not only provide heme iron, but will also further enhance the absorption of the non-heme iron sources through the meat factor.

Avoiding foods containing calcium, polyphenols, and certain proteins around your iron-rich meals is also a useful strategy to maximize iron absorption. Common breakfast foods such as yogurt, milk and cheese contain both calcium and milk proteins (whey and casein) that hinder absorption of iron (3), and coffee and tea have polyphenols, and the protein in eggs, albumin, are also inhibitors of absorption (3). Grouping these foods together, and apart from meals that contain more iron, is an example of ways to keep these foods in your diet without hindering your iron absorption.

Phytates are very common in many foods such as all produce and grains, however studies have shown the inclusion of vitamin C containing foods can override the negative effects of phytates and thus their impact can be seen as negligible in a balanced diet (2,3).

Lastly, cooking in cast iron pans or pots has been shown to be a good source of dietary iron (3,8) and significantly increases the iron content in cooked foods, especially meat and legumes (8). Purchasing this type of cookware may be a valuable investment if you have concerns about meeting your daily iron intake.

Conclusions

Iron homeostasis is essential for optimal health, and as there is no significant excretory pathway for iron in the body, iron levels are mainly regulated at the level of absorption in the intestine (2). Combinations of dietary enhancers and inhibitors of iron absorption can be used to either promote increased or decreased iron storage (and thus ferritin levels) in the body based on individual needs.

Key takeaway: An overall balanced diet is the most important nutritional practice in managing healthy ferritin levels in the body over time. Multiple studies have noted that the inhibitory effects of the compounds mentioned above (polyphenols, phytates, etc.) are exaggerated when the effects after single meals are observed versus the effect over multiple meals (3). However, these interactions remain an important consideration for those who do not consume meat in their regular diet (3,4,5). 

Disclaimer*

The reference ranges and insights presented in Chromacare Wellness Hub articles are meant to improve understanding and provide context, however you should consult with your physician for a formal interpretation of your own results. None of the information within these Chromacare blog posts are meant to be or should be taken as personal medical advice. 

References and Further Reading

Scientific Studies and Articles:

1. Plays, M., Müller, S., & Rodriguez, R. (2021). Chemistry and biology of ferritin. Metallomics, 13(5). https://doi.org/10.1093/mtomcs/mfab021
   
2. Abbaspour, N., Hurrell, R., & Kelishadi, R. (2014). Review on iron and its importance for human health. Journal of Research in Medical Sciences , 19(2), 164–174. PMID: 24778671
   
3. Piskin, E., Cianciosi, D., Gulec, S., Tomas, M., & Capanoglu, E. (2022). Iron absorption: Factors, limitations, and improvement methods. ACS Omega, 7(24), 20441–20456. https://doi.org/10.1021/acsomega.2c01833
   
4. Sharma, S., Khandelwal, R., Yadav, K., Ramaswamy, G., & Vohra, K. (2021). Effect of cooking food in Iron Pot and with iron ingot on increase in hemoglobin level and iron content of the food. Nepal Journal of Epidemiology, 11(2), 994–1005. https://doi.org/10.3126/nje.v11i2.36682
   
5. Perzia, B. M., Ying, G.-S., Dunaief, J. L., & Dunaief, D. M. (2022). Reduction in ferritin concentrationsamong patients consuming a dark-green leafy vegetable–rich, low inflammatory foods everyday (life) diet. Current Developments in Nutrition, 6(6). https://doi.org/10.1093/cdn/nzac095
   
   

Educational Resources:

1. Iron - Fact sheet for health professionals. Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/. Accessed June 4, 2024.
   
2. Cafasso, J. (2024, January 1). What You Need to Know About Iron. Healthline. https://www.healthline.com/health/iron-nutrient
   
3. Vitamin C — Fact sheet for consumers. Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminC-Consumer/. Accessed June 3, 2024.
   
4. Rung, R. (2023, November 3). How Does Calcium Benefit Your Body and How Much Do You Need?. Healthline. https://www.healthline.com/health/calcium
   
5. Harvard T.H. Chan School of Public Health. (2023, March 9). Iron. The Nutrition Source . https://nutritionsource.hsph.harvard.edu/iron/