This largely comes down to the fact that heme iron, or animal based iron is more easily absorbed than plant based iron. On average it's about twice as hard for the body to absorb plant based iron. As such vegetarians and vegans typically need a lot more iron than people who get it from meat sources.
Iron is of course essential when it comes to making hemoglobin, the molecule responsible for transporting oxygen from the lungs.
This isn't just important for athletes who require extra energy and oxygen to push their bodies to the limit, but for it to function in general. And of course this is even more prevelant for women due to their menstrual cycle. This is why it becomes a particular issue for vegans and vegetarians.
The Importance of Iron
Without enough iron, the amount of energy available in cells is limited, with mild deficiency often leading to fatigue. Iron is also involved in the production of myoglobin, a molecule that transports oxygen within muscle cells, as well as various enzymes and other important functions in the body. 
Forms of Dietary Iron: Heme Iron vs Non-Heme Iron
There are two main forms of dietary iron: heme iron and non-heme iron. Heme iron is found in animal-based foods and is more easily absorbed by the body compared to non-heme iron, which is present in plant-based sources. Heme iron is part of the protein structure of hemoglobin and contains one iron molecule that binds to one oxygen molecule, allowing for efficient oxygen delivery. Non-heme iron, on the other hand, is bound to salts or organic chelates and is less readily absorbed. 
Absorption Differences of Plant Based and Animal Based Iron
The absorption of iron varies depending on its form. Heme iron has a higher absorption rate of around 14-18%, whereas non-heme iron is absorbed at a lower rate of 5-12%. However, there are factors that can enhance or inhibit iron absorption.
The Prevalence of Iron Deficiency Among Vegetarians
Several studies suggest that vegetarians may be more prone to iron deficiency compared to non-vegetarians. Aside from the issues from the absorption rates of plant based iron vegetarians is the presence of phytic acid in plant-based diets, which inhibits iron absorption. 
And this is even more prevelant during menopause.A study involving premenopausal women revealed that vegetarians had lower serum ferritin levels, a key indicator of total body iron stores, compared to non-vegetarians. 
Recommended Iron Dosage for Vegans
The recommended iron intake varies depending on age, sex, and life stage. However, vegans may need 1.8 times more iron than non-vegetarians due to the lower bioavailability of non-heme iron. For adult men and postmenopausal women, the daily intake recommendation is 14mg, while premenopausal women require 33mg. While a very well planned out vegan diet can provide enough of most nutrients (with the exclusion of Omega 3, read more here), it may be challenging for some individuals, especially premenopausal women.
The Signs of Iron Deficiency
It's important for vegans and vegetarians to be able to identify the signs of iron deficiency that can lead to anemia. Anemia being condition where the body lacks enough healthy red blood cells to carry adequate oxygen to its tissues. The most common signs of iron deficiency include:
- pale skin
- cold hands and feet
- difficulty concentrating
While anyone can develop iron deficiency anemia, individuals following vegetarian and vegan diets are at a higher risk, primarily due to the lower bioavailability of non-heme iron.
Enhancing Iron Absorption
To increase iron absorption, vegans and vegetarians can incorporate the following strategies into their diets:
Pair Iron-Rich Foods with Vitamin C: Vitamin C enhances iron absorption, regardless of the source. Including foods high in vitamin C, such as citrus fruits, bell peppers, kiwi, broccoli, strawberries, tomatoes, cantaloupe, cooked cabbage, and potatoes, can significantly improve iron absorption when consumed alongside iron-rich plant foods. 
Modify Food Preparation Techniques: Using iron cookware, especially for cooking acidic foods, can help solubilize iron from the pan and increase its bioavailability. This is particularly beneficial for vegans and vegetarians cooking plant-based meals. However, the effectiveness of cast iron pans in increasing iron levels can vary depending on factors such as the frequency of use and the size of the pan. 
Optimize Food Combinations: Consuming iron-containing foods with sources of vitamin C can enhance iron absorption. Additionally, it is important to limit the intake of inhibitory foods, such as coffee and tea, which can reduce iron absorption. Consuming these inhibitory foods between meals instead of with iron-rich foods can help mitigate their impact. 
Increase Consumption of Plant-Based Iron Sources: Including a variety of plant-based iron sources in the diet is crucial for vegans and vegetarians. Some of the best plant-based sources of iron include lentils, soybeans, tofu, fortified cereals, brown rice, oatmeal, nuts and seeds, and green leafy vegetables like spinach and broccoli. These foods can provide the necessary iron to meet the increased iron needs of athletes following a plant-based diet.
Consider Iron Supplementation: Iron supplementation may be necessary for certain high-risk groups, such as pregnant women. Ferrous iron salts, such as ferrous sulfate and ferrous gluconate, are commonly used for oral supplementation due to their affordability and high absorption rates. However, it is important to consult with a healthcare professional before starting any supplementation regimen.
Should Vegetarians and Vegans Take Iron Supplements?
As we've mentioned vegetarians and vegans have a higher risk of iron deficiency due to plant based iron being more dificult to aborb than heme iron and due to their diets containing more phytic acid which hinders iron absorption further. Resulting in them needing up to 1.8 times as much iron as their meat eating counterparts. While it is possible to obtain sufficient iron from a vegetarian diet, some individuals may require iron supplements to meet their needs. Particularly pre menopausal women, due to them neededing up to 33mg of iron daily. It is worth vegetarians and vegans getting a check if they suspect that their iron levels may be too low. Particularly if they are experiencing, fatigue, cold hands and feet, pale skin or difficulty concentrating.
The Best Types of Iron Supplements
Not all forms of iron supplements are created equal. Common forms of iron supplements include ferrous sulfate, ferrous fumarate, ferrous gluconate, and iron bisglycinate. While ferrous sulfate is commonly prescribed, it is often associated with gastrointestinal side effects. Ferrous fumarate and ferrous gluconate are alternatives, but they are often just as bad. On the other hand, iron bisglycinate, a chelated form of iron, has been found to be more bioavailable and less likely to cause gastric distress.
Inhibiting Iron Absorption
While it is important to enhance iron absorption, it is also essential to be aware of factors that can inhibit iron absorption. Phytates found in grains and legumes, as well as certain polyphenols, can reduce iron absorption. However, for individuals following a mixed diet, the impact of these inhibitory compounds may be less pronounced unless they adhere to a strict vegan diet.
Fortified and Enriched Foods
Fortified and enriched foods can be valuable sources of iron for vegans and vegetarians. Enriched foods have nutrients added back after processing, while fortified foods have additional nutrients that were not originally present. These fortified and enriched products can provide an extra boost of iron in a convenient and accessible way.
Conclusion: Why Vegetarians and Vegans Need More Iron
Increasing iron absorption in vegans and vegetarians is essential for maintaining optimal iron levels and supporting overall health and athletic performance. By implementing strategies such as pairing iron-rich foods with vitamin C, modifying food preparation techniques, increasing consumption of plant-based iron sources, and considering iron supplementation, vegans and vegetarians can ensure they meet their iron needs. Additionally, incorporating fortified and enriched foods, as well as alternative methods like cooking with cast iron pans. Although there are other nutrients that vegans and vegetarians are more likely to be lacking in.
Remember, if you have any concerns or specific dietary needs, it is always best to consult with a healthcare professional or registered dietitian to receive personalized advice and guidance.
1 - https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
2 - https://pubmed.ncbi.nlm.nih.gov/17056805/
3 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8537570/
4 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6367879/
5 - https://pubmed.ncbi.nlm.nih.gov/6940487/
6 - https://pubmed.ncbi.nlm.nih.gov/12859709/
7 - https://pubmed.ncbi.nlm.nih.gov/6402915/