Iron is a vital mineral for oxygen transportation and energy production. It's well-known that insufficient intake of iron can lead to iron deficiency anaemia. This condition causes symptoms such as lethargy, poor concentrations, pale skin, fragile nails and so on. In severe cases, patients can experience breathlessness, angina and even heart failure. It's therefore incontestable that getting enough iron from food is imperative for good health and well-being.
However, there is considerable uncertainty in respect to how much iron those on vegetarian and vegan diets need. In 2001 the National Academy of Medicine (NAM) proposed that vegetarians need 1.8 times the recommended daily allowance (RDA) and suggest that vegans may require even more than this!1. On the other hand, the European Food Safety Authority (EFSA) holds that European vegetarians do not need to aim for higher intakes2. These vastly different assessments of iron requirements in vegetarians are underpinned by divergent judgements in relation to the importance of the lower bioavailability of iron in meat-free diets.
There are three main reasons why iron in veg*n (vegetarian + vegan) diets is of lower bioavailability:
1. Higher intake of phytate
Plant-based eaters tend to consume greater amounts of wholegrains, legumes and nuts. A great deal of evidence indicates that these foods improve health outcomes. However, they are a rich source of phytic acid: a known inhibitor of iron bioavailability3. Phytate forms bonds with iron and thereby reduces its absorption.
2. The lack of heme iron
Iron can be divided into two types: heme and non-heme. All iron found in edible plants and fungi is non-heme. Heme is found in animal products (particularly animal flesh). Heme iron is more bioavailable and less affected by dietary inhibitors compared to non-heme iron.
3. Avoidance of animal flesh
Animal tissues are a key enhancer of non-heme iron bioavailability. Randomized controlled trials have established that consumption of animal flesh increases absorption of non-heme iron4,5,6,7. Moreover, this lines up with observational evidence which finds higher intakes of animal flesh to be inversely associated with iron deficiency anaemia8, 9.
Veg*n diets and serum ferritin
Serum ferritin is a marker of iron status – this is because ferritin is an iron-storing protein. Surprisingly, in short-term clinical trials manipulating iron bioavailability does not significantly move this marker10, 11, 12. Of particularly relevance, a 16-week randomized crossover trial that tracked iron absorption via radioactive labelling confirmed that iron absorption is lower in vegetarian diets; but no significant change in serum ferritin was observed10.
It seems that in the short-term the body adapts to changes in iron bioavailability to maintain stable iron levels. In other words, the body appears to absorb iron more efficiently when presented with less bioavailable sources10, 11, 13. However, would such adaptation be sufficient indefinitely? Might iron stores deplete over time? There is some evidence to suggest that this may be the case. In cross-sectional studies vegans are consistently shown to display lower serum ferritin values14,15. More importantly, there is a trend for vegans to show higher rates of very low ferritin levels16,17,18; as well as very low haemoglobin (another important marker of iron status) 18,19.
However, ferritin does not only reflect iron status. Ferritin levels tend to be higher in overweight/obese individuals and in those with other inflammatory diseases. Since veg*an diets are associated with lower BMI20,21 and lower inflammatory markers22, the lower ferritin levels within this populations are likely to be confounded to some extent.
A recent large cross-sectional study controlled for these potential confounders23. When individuals with overweight/obesity or raised hs-CRP (an inflammatory marker) were excluded from the analysis, there were no statistically significant differences in the percentage of those with iron deficiency (defined as ferritin <30mcg/L) between veg*n males and omnivorous males (3.3% vs 0%) or between veg*n non-menstruating women and omnivorous non-menstruating women (14% vs 5%). However, veg*n menstruating females still showed statistically significant higher rates of iron deficiency compared to omnivorous menstruating females (51% vs 32%).
These results suggest that veg*n males only have a slightly higher risk of iron deficiency, at most. Whereas the data are suggestive of a greater risk among veg*n non-menstruating females and we can be relatively confident that veg*n menstruating females are at higher risk of deficiency. Now, menstruating females in general are at high risk of iron deficiency. In my estimation, it's plausible to speculate that the lower iron bioavailability of veg*n diets compounds this tendency.
Iron intake among veg*ns
I have found several studies that estimate iron intake among male vegans and all of them showed intakes above the RDA for males (8mg per day)24, 25, 26, 27, 28, 29, 30. In fact, average intake invariably surpassed 14.4mg per day (8mg x 1.8), which is the RDA for vegetarian males as per NAM.
Contrariwise, most studies on female vegans observed intakes below the RDA for nonvegetarians females of childbearing age (18mg) and far below the proposed RDA for female vegetarians of childbearing age (32.4mg)24,25, 26, 27. Although in two studies, vegan females consumed around 20mg per day28,29.
That male vegans are more likely to consume enough iron is not unexpected. Firstly, iron targets are lower for males. Secondly, men typically consume greater amounts of food.
In my estimation, vegans should consume above the RDA for iron, due to lower iron bioavailability.
Vegan males tend to naturally consume iron above the RDA for vegetarians and given that they show low rates of deficiency, I think they should continue consume iron at this level.
The situation with vegan women is complicated. Vegan females typically consume below the RDA for non-vegetarians and appear to be at higher risk of deficiency compared to their nonvegetarian counterparts. The RDA for vegetarians is a reasonable and readily achievable target for non-menstruating females . However, the RDA for vegetarians of childbearing age is arguably impractically high (32.4mg) and it is not clear to me whether this is justified. However, I do think that menstruating females should hit and ideally exceed the RDA for non-vegetarian females.
Suggestion for vegan adult males:
Aim for at least 14.4mg (1.8 x RDA).
Obtain plenty of vitamin C (a known enhancer of iron bioavailability).
Suggestion for vegan adult females:
Non-menstruating females should aim for at least 14.4mg (1.8 x RDA).
Menstruating females should aim to exceed 18mg.
Obtain plenty vitamin C.
A low-dose supplement is an option for those that struggle to meet their requirements.
Note: Athletes are likely to have higher iron needs.
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7. Mayer Labba, I.C., Hoppe, M., Gramatkovski, E., Hjellström, M., Abdollahi, M., Undeland, I., Hulthén, L. and Sandberg, A.S., 2022. Lower non-Heme iron absorption in healthy females from single meals with texturized fava bean protein compared to beef and cod protein meals: two single-blinded randomized trials. Nutrients, 14(15), p.3162.
8. Papier, K., Fensom, G.K., Knuppel, A., Appleby, P.N., Tong, T.Y., Schmidt, J.A., Travis, R.C., Key, T.J. and Perez-Cornago, A., 2021. Meat consumption and risk of 25 common conditions: outcome-wide analyses in 475,000 men and women in the UK Biobank study. BMC medicine, 19(1), pp.1-14.
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