Are Vegans Chronically Iron Deficient?
The omnivorous lay person's biggest worry for my health as a vegan, after my protein intake (and if you're worried, don't be. Check out my article Vegans vs Protein!), is where I get my iron. My response is usually simply: "From plants." (Because, well, duh. I only eat plants.) But what is the scientific reality of reaching my Daily Recommended Intake of iron on a plant-based diet? Get ready for some science, dear readers. Once I finish singing the Bill Nye the Science Guy theme song, of course.
First things first...
What is iron anyway?
Iron is a mineral found in nature which is essential to the normal functioning of the human body. Iron is a major component of hemoglobin, the oxygen binding protein of red blood cells which transfers oxygen from the lungs to all of the tissues of the body. Iron is also a component of the oxygen storage unit of muscle cells, myoglobin, which provides working muscles with oxygen.
Iron is necessary for proper human growth and development as well as normal cellular functioning and synthesis of some hormones and connective tissues. Both myoglobin and hemoglobin have a molecular constituent called heme which allows them to combine reversibly with oxygen. Iron can be found in the foods we eat as either heme or non-heme iron.
What's the difference between heme and non-heme iron?
Dietary iron has two main forms: heme and non-heme. Heme iron is formed when non-heme iron combines with protoporphyrin IX (a naturally occurring molecule in the body). This combination can happen before the iron is absorbed or within the body after it is ingested Plants, fortified foods, and supplements contain only non-heme iron while meat (including seafood and poultry) contains both non-heme (~55-60%) and heme (~40-45%) iron. Meat, especially red meat, is the best known source of heme iron. This is because when humans eat meat they consume the blood proteins (hemoglobin) and muscle proteins (myoglobin) contained in the flesh of the animal. The animal in question created heme iron in its body while it was still alive by combining the non-heme iron it ingested in its food with the essential molecules generated in its body. Those who eat meat are taking advantage of this pre-completed process.
The good news for vegans and vegetarians out there is that humans can survive on a diet that provides solely non-heme iron. Once the non-heme iron is absorbed in our bodies it is combined with protoporphyrin IX and is put to work storing and transporting oxygen in our cells. But if non-heme iron is a perfectly acceptable sole source of iron in a human's diet, why does everyone claim that eating heme iron is better? Bioavailability is the answer.
Bioavailability is a complicated thing. Researchers don't agree on the exact percentages of each type of iron that we can absorb, and the exact absorption rate is influenced by a whole host of factors. We know that iron differs from other minerals because its balance in the body is regulated entirely by absorption; as there is no physiologic mechanism for the excretion of iron. Algorithms have been developed to estimate bioavailability in single meal studies, however, these algorithms tend to underestimate bioavailability and data from single meal studies exaggerates the effects of individual dietary factors on iron absorption. The only thing researchers DO agree on is that the human body is able to absorb a higher percentage of heme iron than it can non-heme iron that it ingests, in general. The percentages vary from study to study but an example of estimated absorption rates is as follows: non-heme iron 7-11% and heme iron 15%.
So if we don't know the exact bioavailability of each type of iron, what do we know? Much research has been done on the topic of inhibitors and enhancers of iron absorption. Here is a quick list of some of the known factors that can have an effect.
Iron Absorption Inhibitors:
- Phytates are found in whole grains, legumes, nuts, and seeds. They are able to bind to certain dietary minerals including iron, zinc, manganese, and calcium, and can slow their absorption into the body. However, those eating a balanced diet needn't worry about phytates. As a vegetarian or vegan, reducing your intake of wheat bran, as well as cooking and soaking grains before eating them can help diminish the effect of phytates. It's also good to remember that phytates also have positive health benefits including reducing inflammation, lowering food's glycemic load, reducing cardiovascular disease, and stopping the proliferation of cancer cells in laboratory research.
- Polyphenols in black tea, herb tea, wine, and spices can have an effect on non-heme iron absorption depending on their quantity and type. It was shown on a study of Thai women that while turmeric contains more polyphenols than chili, chill had a greater inhibiting effect on iron absorption.
- Calcium was shown to inhibit both heme and non-heme iron absorption in single meal studies, whether it was derived from diet or from supplements.
- Dairy & Eggs. The 2 main types of milk protein, casein and whey, have been shown to inhibit non-heme iron absorption in humans while egg whites added to a meatless meal reduced iron absorption by a whopping 72% in this study.
Iron Absorption Enhancers:
- Ascorbic Acid is a form of vitamin C found in citrus fruits, peppers, cruciferous and leafy vegetables, and more. Many studies have demonstrated its ability to enhance iron absorption and its ability to negate the inhibiting effects of the compounds listed above. Some studies indicate that including ascorbic acid in a meal can increase iron absorption by as much as triple! Cooking and other processing can damage ascorbic acid, removing its enhancing effect.
- Depleted Iron Stores. Iron absorption rates vary wildly between those individuals with sufficient iron and those who are iron depleted. One study found that the estimated absorption of iron in premenopausal women ranged from 13% in women with sufficient iron to 31% in women with depleted iron levels.
Dietary inhibitors and enhancers only affect the absorption of the iron being consumed around the same time, while other factors such as depleted iron stores, genetic disorders, inflammation, obesity, and deficiency in other nutrients in the body affect total iron absorption.
How Much Iron Should You Be Getting Daily?
The table below shows recommended intakes in mg/day.
It is generally recommended that vegetarians and vegans get 1.8 times the normal recommended amount of iron daily to compensate for lower absorption rates of non-heme iron. Vegan and vegetarian numbers (those above multiplied by 1.8) are in the table below.
What vegan foods contain iron?
Legumes: soybeans (9mg/cup), lentils (6.5mg/cup), white beans and chickpeas (5mg/cup), tofu and kidney beans (4mg/cup - as much as 5 ounces of sardines)
Grains: quinoa (3mg/cup), brown rice (1mg/cup - equivalent to 3oz of tuna)
Nuts & Seeds: pine nuts (7.5mg/cup - 3 times as much iron as in a cup of turkey), sunflower seeds (5mg/cup), pumpkin seeds (2mg/cup),
Vegetables: tomato paste (8mg/cup - equal amount of iron as in 12oz of ground beef), cooked spinach (6.5mg/cup)
Other: spirulina (32mg/cup - as much iron as is in 53 large hard-boiled eggs), blackstrap molasses (16mg/cup), prune juice (3mg/cup), dried apricots (3.5mg/cup)
So, is it possible to get enough iron on a vegan diet?
Lets say you're the same 25 year old woman we mentioned earlier. Your meat-eating contemporaries are recommended 18mg/day, but you (as a vegan) are told you need 1.8 times that amount daily, or 32.4mg/day. Is it possible?
A meal with 1.5 cups of lentils (9.75mg), 1 cup of tofu (4mg), and 3 cups of cooked spinach (19.5mg) has already surpassed your daily iron needs coming in at over 33mg. And what if you added half a cup of tomato paste (4mg) blended with a tbsp of spirulina (2mg) as a sauce? You'd be approaching the upper levels of what is considered safe iron intake for a day, in one meal. As you can see, a well-planned, balanced diet of whole, nutrient rich foods can easily reach the required iron needs, even taking into account poor absorption rates.
How high is too high: Iron Overdose
There is little risk of iron overload from diet in adults with normal intestinal function, however, acute intake of more than 20mg of iron per kg of bodyweight from supplements or medication can lead to many unpleasant side effects including constipation, nausea, abdominal pain, vomiting, gastric upset, and faintness. A true overdose of iron (around 60mg in one dose) can lead to multisystem organ failure, coma, convulsions, and even death.
How low is too low: Iron Depletion & Iron Deficiency Anemia
But what if you get enough iron through your food and then lose it? Iron loss through urine, feces, the gastrointestinal tract, and the skin is minimal, however, the major concern is iron loss during menstruation in women, due to the loss of blood. There have been various reliable tests developed over the years to detect early iron store depletion (measuring serum ferritin, a protein found within the cells that store iron in the body), advanced iron depletion (determined by reduced serum iron, amongst other indicators), and iron deficiency anemia (when hemoglobin concentrations in the blood drop below 13g/dL in men and 12g/dL in women). Women should remain aware of their iron intake, especially during their menstruation period, to maintain adequate iron stores in the body.
Iron deficiency is one of the most common nutritional deficiencies, affecting mostly children and women of childbearing age. Anemia symptoms include gastrointestinal disturbances, extreme fatigue, impaired cognitive and immune function, pale skin, impaired temperature regulation, dizziness and headaches. If you recognize these symptoms in yourself please go see a doctor and get tested.
So, are vegans chronically iron deficient?
No. A vegan diet, without supplementation, is completely satisfactory for maintaining healthy iron levels in the body. If you are concerned about absorbing enough of the iron you eat, try combining foods high in ascorbic acid with your meals, soaking your grains, and avoiding tea and wine close to meal time. If you're the type who likes to take extra precautions you can take daily iron supplements to ensure full stores. Just make sure you aren't taking to much! If you keep these things in mind you should have no problem maintaining sufficient iron levels for all of your oxygen storing and transporting needs. Happy blood, happy body. Happy body, happy you!
Until next time...
Do you track your iron intake? What are your thoughts on iron supplementation? Let me know in the comments below!
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