In 2016, the German Society for Nutrition cautioned against a vegan diet for babies, children, and adolescents, and during pregnancy and breastfeeding, due to insufficient data.[22] In 2020, the German Society for Nutrition issued an update stating that they do not recommend a vegan diet for babies, children and adolescents, or for pregnancy or breastfeeding, citing insufficient data for these subpopulations.[23]
The Danish Health Authority have advised vegan parents to seek professional dietary advice, noting that "young children who are fed a vegan diet can grow and develop normally if they receive the right supplements to the diet, and the energy content is sufficient. It requires detailed knowledge of diet and nutritional needs. The parents must therefore be encouraged to seek advice from a licensed clinical dietitian to ensure that the child's diet is sufficient."[24] The National Institute for Health and Welfare in Finland have stated that a well-balanced vegan diet is safe during pregnancy but mothers require the guidance of a nutritional therapist.[25]
The State of Israel Ministry of Health advises vegan mothers to consult with a dietitian.[26] The Swiss Federal Commission for Nutrition do not recommend vegan diets for pregnant women, infants and children or older adults due to lack of data and risk of certain nutrient deficiencies.[27] The Royal Academy of Medicine of Belgium do not recommend a vegan diet during pregnancy, breastfeeding and infancy.[28]
The German Society for Allergology and Clinical Immunology (DGAKI) position paper on vegan diets in 2023 noted that "to ensure an adequate supply of vitamin B12, but also of calcium, iron, iodine, zinc, as well as high-quality protein and long-chain omega-3 fatty acids (EPA/DHA), an in-depth study of the subject of nutrition, time investment, and supplementation, with regard to various nutrients, is required."[29]
The American Heart Association (AHA) gave the vegan diet a 78% score of its alignment with the 2021 AHA Dietary Guidance. They noted that benefits of a vegan diet are its emphasis on fruits, legumes, nuts, vegetables and whole grains which are heart healthy but a key challenge is its restrictive nature and risk of Vitamin B12 deficiency.[30]
Position of paediatric associations
The position of the Canadian Paediatric Society is that "well-planned vegetarian and vegan diets with appropriate attention to specific nutrient components can provide a healthy alternative lifestyle at all stages of fetal, infant, child and adolescent growth." It is recommended that attention should be given to nutrient intake, particularly protein, vitamins B12 and D, essential fatty acids, iron, zinc, and calcium.[31]
Although position papers from America and Canada have stated that well-planned vegan diets, are suitable for every stage of life, European statements have been more cautious of vegan diets in pregnancy and infancy.[32] The British Paediatric Association (BPA), European Paediatric Association (EPA), European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN), Croatian Society for Pediatric Gastroenterology, Hepatology and Nutrition (HDPGHP) and the Italian Society of Paediatrics (SIP) have included strong recommendations to parents that vegan diets should not be adopted by pregnant women and infants without medical or dietetic supervision.[33][34][35][36][37]
The German Society for Paediatric and Adolescent Medicine, Polish National Consultant in the Field of Paediatrics and Spanish Paediatric Association do not recommend
vegan diets during infancy or childhood and instead advise a balanced omnivorous or lacto-ovo-vegetarian diet to meet nutritional requirements.[38][39][40]
The French Pediatric Hepatology, Gastroenterology and Nutrition Group have stated that a vegan diet is "not recommended for infants, children, and adolescents due to the risk of multiple nutritional deficiencies that are inevitable in the absence of supplements".[41] In 2017, the Italian Society of Preventive and Social Pediatrics (SIPPS), together with the Italian Federation of Pediatricians (FIMP) and the Italian Society of Perinatal Medicine (SIMP) issued a joint position paper which concluded that vegan diets cannot be recommended for children because the diet leads to deficiencies in vitamin B12, calcium, DHA, iron and vitamin D. When these nutrients are missing, it negatively affects children's growth and neurocognitive development.[42]
The Slovenian Paediatric Society have advised against vegan diets for pregnant and lactating women, newborns, infants, children, and adolescents.[43]
According to a 2015 systematic review, there was little evidence available about vegetarian and vegan diets during pregnancy, and a lack of randomized studies meant that the effects of diet could not be distinguished from confounding factors.[44] It concluded: "Within these limits, vegan-vegetarian diets may be considered safe in pregnancy, provided that attention is paid to vitamin and trace element requirements."[44] A daily source of vitamin B12 is important for pregnant and lactating vegans, as is vitamin D if there are concerns about low sun exposure.[45] A different review found that pregnant vegetarians consumed less zinc than pregnant non-vegetarians, with both groups' intake below recommended levels; however, the review found no significant difference between groups in actual zinc levels in bodily tissues, nor any effect on gestation period or birth weight.[46]
Researchers have reported cases of vitamin B12 deficiency in lactating vegetarian mothers that were linked to deficiencies and neurological disorders in their children.[47][48] The UK National Health Service recommends that a physician or registered dietitian should be consulted about taking supplements during pregnancy.[49][50]
A 2022 French expert consensus paper recommended a minimum of 800 IU and a maximum of 1600 IU of vitamin D per day for vegan children aged 2-18 years.[51]
Public reaction
Because of the sensitive nature of pregnancy, vegan diets have attracted significant attention from the media, both positive and negative. Much of the reaction has focused on nutrition.
Negative attention stems from cases of nutritional deficiencies that have come to the attention of the courts, including the death of a baby in New Zealand in 2002 due to hypocobalaminemia, i.e. vitamin B12 deficiency.[52][53] Positive attention includes in 2018 when journalist Rebecca Seal of The Guardian reported on the growing number of vegan children in the United Kingdom and cited guidance issued by the British Dietetic Association in 2017 that well-planned vegan diets are safe for all ages.[54] In 2017, BBC Good Food published a guide to vegan feeding for children and infants.[55] In 2016, journalist Avery Yale Kamila of the Portland Press Herald wrote about raising a giant baby on a vegan diet who was wearing 24 months clothing at six months.[56]
Critical nutrients
The American Academy of Nutrition and Dietetics states that special attention may be necessary to ensure that a vegan diet will provide adequate amounts of vitamin B12, omega-3 fatty acids, vitamin D, calcium, iodine, iron, and zinc.[1] These nutrients are available in plant foods, with the exception of vitamin B12, which can be obtained only from B12-fortified vegan foods or supplements.[57]Iodine may also require supplementation, such as using iodized salt.[1]
Vitamin B12 is not made by plants or animals, but by bacteria that grow in soil, feces, dirty water, the intestines of animals or laboratories,[58][59][60][61][62] so plant foods are not reliable sources of B12.[63] It is synthesized by some gut bacteria in humans and other animals, but humans cannot absorb the B12 made in their guts, as it is made in the colon which is too far from the small intestine, where absorption of B12 occurs.[64]Ruminants, such as cows and sheep, absorb B12 produced by bacteria in their guts.[64]
Animals store vitamin B12 in liver and muscle and some pass the vitamin into their eggs and milk; meat, liver, eggs and milk are therefore sources of B12.[65][66]
Vitamin B12 deficiency is potentially extremely serious, leading to megaloblastic anemia (an undersupply of oxygen due to malformed red blood cells),[71] nerve degeneration and irreversible neurological damage.[72] Cases of severe vitamin B12 deficiency have been reported in vegan adults, children[73] infants and toddlers.[74]
Because B12 is stored in large amounts in the liver, deficiency in adults may begin only years after adoption of a diet lacking B12. For infants and young children who have not built up these stores, onset of B12 deficiency can be faster and supplementation for vegan children is thus crucial.
Evidence shows that vegans who are not taking vitamin B12 supplements do not consume sufficient B12 and often have abnormally low blood concentrations of vitamin B12.[75] This is because, unless fortified, plant foods do not contain reliable amounts of active vitamin B12. Vegans are advised to adopt one of the following dietary options:[76]
consume fortified foods 2-3 times per day to get at least 3 micrograms of vitamin B12,
or take at least 10 micrograms of B12 as a supplement once per day,
or take at least 2000 micrograms of B12 as a supplement once per week.
B12 is more efficiently absorbed in small regular doses, which explains why the quantity required rises so quickly as frequency goes down.
The US National Institutes of Health recommends B12 intake in a range from 0.4 micrograms a day for infants, to 2.4 micrograms for adults, and up to 2.8 micrograms for nursing mothers.
[77]
The European Food Safety Authority set the Adequate Intake at 1.5 micrograms for infants, 4 micrograms for children and adults, and 4.5 and 5 micrograms during pregnancy and nursing.[78] These amounts can be obtained by eating B12 fortified foods, which include some common breakfast cereals, plant milks, and meat analogues, as well as from common multivitamins such as One-A-Day. Some of the fortified foods require only a single serving to provide the recommended B12 amounts.
[79]
It has been suggested that nori (an edible seaweed), tempeh (a fermented soybean food), and nutritional yeast may be sources of vitamin B12.[80][81] In 2016, the Academy of Nutrition and Dietetics stated that nori, fermented foods (such as tempeh), spirulina, chlorella algae, and unfortified nutritional yeast are not adequate sources of vitamin B12 and that vegans need to consume regularly fortified foods or supplements containing B12. Otherwise, vitamin B12 deficiency may develop, as has been demonstrated in case studies of vegan infants, children, and adults.[82]
Vitamin B12 is mostly manufactured by industrial fermentation of various kinds of bacteria, which make forms of cyanocobalamin, which are further processed to generate the ingredient included in supplements and fortified foods.[83][84] A Pseudomonas denitrificans strain was most commonly used as of 2017[update].[85][86] It is grown in a medium containing sucrose, yeast extract, and several metallic salts. To increase vitamin production, it is supplemented with sugar beet molasses, or, less frequently, with choline.[85] Certain brands of B12 supplements are certified vegan.[87]
Iodine
Humans require iodine for the production of thyroid hormones that enable normal thyroid function.[88] Iodine supplementation may be necessary for vegans in countries where salt is not typically iodized, where it is iodized at low levels, or where, as in Britain and Ireland, dairy products are relied upon for iodine delivery because of low levels in the soil.[89] Iodine can be obtained from most vegan multivitamins or regular consumption of seaweeds, such as kelp.[90]
Vegan diets typically require special attention for iodine, for which the only substantial and reliable vegan sources are sea vegetables, iodized salt and supplements. The iodine content of sea vegetables varies widely and may provide more than the recommended upper limit of iodine intake.[1]
A 2023 review found that vegans have lower iodine compared with people consuming omnivorous diets.[91]
Proteins are composed of amino acids. Vegans obtain all their protein from plants, omnivores usually a third, and ovo-lacto vegetarians half.[92] Sources of plant protein include legumes such as soy beans (consumed as tofu, tempeh, textured vegetable protein, soy milk, and edamame), peas, peanuts, black beans, and chickpeas (the latter often eaten as hummus); grains such as quinoa, brown rice, corn, barley, bulgur, and wheat (the latter eaten as bread and seitan); and nuts and seeds. Combinations that contain high amounts of all the essential amino acids include rice and beans, corn and beans, and hummus and whole-wheat pita.[93] In 2012, the United States Department of Agriculture stated that soy protein (tofu) may replace meat protein in the National School Lunch Program.[21]
The Academy of Nutrition and Dietetics said in 2009 that a variety of plant foods consumed over the course of a day can provide all the essential amino acids for healthy adults, which means that protein combining in the same meal is generally not necessary.[94]The Dietitian's Guide to Vegetarian Diets writes that there is little reason to advise vegans to increase their protein intake; but erring on the side of caution, the authors recommend a 25 percent increase over the RDA for adults, to 1 g/kg (.45 g/lb) of body weight.[95]
Omega-3 fatty acids
Experts have not established recommended amounts for omega-3 fatty acids, except for ALA.[96] The human body can use ALA to synthesize DHA and EPA. However, this only works efficiently if the ratio between omega 3 (mainly in flaxseed, chia seeds) to omega 6 (mainly in sunflower oil) does not exceed 1:5.[97]
While there is little evidence of adverse health or cognitive effects due to DHA deficiency in adult vegetarians or vegans, fetal and breast milk levels remain a concern.[98]
DHA supplements derived from DHA-rich microalgae are available, and the human body can also convert DHA to EPA.[99]
Calcium
It is recommended that vegans eat three servings per day of a high-calcium food, such as fortifiedplant milks, green leafy vegetables, seeds, tofu, or other calcium-rich foods, and take a calcium supplement as necessary.[1][100]
Vegans consume less calcium than omnivores or vegetarians.[101]
Consuming a vegan diet is associated with lower bone mineral density (BMD).[102][103] It is unclear if the magnitude is clinically relevant,[104] but it seems that vegans tend to have higher fracture rates.[102][103]
However, diet quality is not always considered in studies. High quality vegan or vegetarian diets may therefore afford the same bone health as that of omnivores.[105] Especially when sufficient vitamin D and calcium are consumed there seems to be no difference in bone health.[106]
Iron
It is recommended for vegans to daily eat iron-rich foods in combination with vitamin C, because vitamin C enhances iron absorption.[107][108]
Due to the low absorption rate on non-heme iron, it is recommended to eat dark leafy greens (and other sources of iron) together with sources of vitamin C.[109]
Iron levels of vegans may be of concern because of the limited bioavailability. There are concerns about the bioavailability of iron from plant foods, assumed by some researchers to be 5–15 percent compared to 18 percent from a non-vegetarian diet.[110]Iron-deficiency anemia is found as often in non-vegetarians as in vegetarians. Vegetarians' iron stores are lower. Lower iron stores may increase the risk for iron deficiency. However, as high iron stores are associated with health risks, lower iron stores may be beneficial.[111]
Zinc levels of vegans may be of concern because of the limited bioavailability.[110]
In general zinc intake and serum zinc is lower in vegans.[115]
Phytates can inhibit the absorption of zinc. Depending on the amount of zinc in the diet (low, moderate, high), the German Nutrition Society (DGE) has established three different reference values for intake of zinc.[116][117] For diets that include mostly or exclusively plant-based protein sources the DGE recommends 16mg of zinc per day for men and 10mg of zinc per day for women.[118]
Vitamin D
The main function of vitamin D in the body is to enhance absorption of calcium for normal mineralization of bones and calcium-dependent tissues.[45]
Sunlight, fortified foods, and dietary supplements are the main sources of vitamin D for vegans. Humans produce vitamin D naturally in response to sun exposure and ultraviolet light (UV) acting on skin to stimulate vitamin D synthesis.[45] UV light penetrates the skin at wavelengths between 290 and 320 nanometers, where it is then converted into vitamin D3.[45] Vitamin D2 can be obtained from fungi, such as mushrooms exposed to sun or industrial ultraviolet light, offering a vegan choice for dietary or supplemental vitamin D.[119][120]Plant milks, such as from oat, soy, or almond, and breakfast cereals are commonly fortified with vitamin D.[45]
The recommended daily intake of vitamin D for adults is 600 IU (15 micrograms), and for adults over 70 years old, 800 IU (20 micrograms).[45]
Vitamin D comes in two forms. Cholecalciferol (vitamin D3) is synthesized in the skin after exposure to the sun or consumed from food, usually from animal sources.[45]Ergocalciferol (vitamin D2) is derived from ergosterol from UV-exposed mushrooms or yeast.[45] When produced industrially as supplements, vitamin D3 is typically derived from lanolin in sheep wool. However, both provitamins and vitamins D2 and D3 have been discovered in various species of edible Cladina lichens (especially Cladina rangiferina).[121] These edible lichen are harvested in the wild for producing vegan vitamin D3.[122] Conflicting studies have suggested that the two forms of vitamin D may or may not be bioequivalent.[123] According to 2011 research from the U. S. National Academy of Medicine (then called Institute of Medicine), the differences between vitamins D2 and D3 do not affect metabolism, both function as prohormones, and when activated, exhibit identical responses in the body.[124] Although vitamin D3 is produced in small amounts by lichens or algae exposed to sunlight,[125][126] industrial production in commercial quantities is limited, and there are few supplement products as of 2019.[127]
Choline
Some news reports presented vegan diets as deficient in choline following an opinion piece in the BMJ by a nutritionist affiliated with the meat industry.[128] Although many animal products, like liver and egg, contain high amounts of choline (355 mg/3 oz and 126 mg/large egg, respectively), wheat germ (172 mg/cup), Brussels sprouts (63 mg/cup), and broccoli (62 mg/cup) are also good sources of choline.[129]
^Craig, Winston J (May 2009). "Health effects of vegan diets". The American Journal of Clinical Nutrition. 89 (5): 1627S–1633S. doi:10.3945/ajcn.2009.26736N. PMID19279075. Vegan diets are usually higher in dietary fiber, magnesium, folic acid, vitamins C and E, iron, and phytochemicals, and they tend to be lower in calories, saturated fat and cholesterol, long-chain n–3 (omega-3) fatty acids, vitamin D, calcium, zinc, and vitamin B-12. ... A vegan diet appears to be useful for increasing the intake of protective nutrients and phytochemicals and for minimizing the intake of dietary factors implicated in several chronic diseases.
^Mangels, Reed; Messina, Virginia; and Messina, Mark. "Vitamin B12 (Cobalamin)," The Dietitian's Guide to Vegetarian Diets. Jones & Bartlett Learning, 2011, pp. 181–192.
Mangels, Reed. "Vitamin B12 in the Vegan Diet", Vegetarian Resource Group, accessed December 17, 2012: "Vitamin B12 is needed for cell division and blood formation. Neither plants nor animals make vitamin B12. Bacteria are responsible for producing vitamin B12. Animals get their vitamin B12 from eating foods contaminated with vitamin B12 and then the animal becomes a source of vitamin B12. Plant foods do not contain vitamin B12 except when they are contaminated by microorganisms or have vitamin B12 added to them. Thus, vegans need to look to fortified foods or supplements to get vitamin B12 in their diet."
"Vitamin B12", Office of Dietary Supplements, National Institutes of Health, accessed December 17, 2012.
Norris, Jack. "Vitamin B12: Are you getting it?", Vegan Outreach, July 26, 2006: "Contrary to the many rumors, there are no reliable, unfortified plant sources of vitamin B12 ... [There is an] overwhelming consensus in the mainstream nutrition community, as well as among vegan health professionals, that vitamin B12 fortified foods or supplements are necessary for the optimal health of vegans, and even vegetarians in many cases. Luckily, vitamin B12 is made by bacteria such that it does not need to be obtained from animal products."
^Melina, Vesanto; Craig, Winston; Levin, Susan (December 2016). "Position of the Academy of Nutrition and Dietetics: Vegetarian Diets". Journal of the Academy of Nutrition and Dietetics. 116 (12): 1970–1980. doi:10.1016/j.jand.2016.09.025. ISSN2212-2672. PMID27886704. S2CID4984228.
^Silva, Sandra Cristina Gomes; Pinho, João Pedro; Borges, Cátia; Santos, Cristina Teixeira; Santos, Alejandro; Graça, Pedro. (2015). "Guidelines for a Healthy Vegetarian Diet". National Programme for the Promotion of Healthy Eating. Retrieved 5 December 2022. "When appropriately planned, vegetarian diets, including lacto-ovo vegetarian or vegan, are healthy and nutritionally adequate for all cycles of life, and they can be useful in prevention and treatment of some chronic diseases. However, as in any food pattern, vegetarian diets may be inadequate."
^ abLong, Cynthia (22 February 2012). "Crediting Tofu and Soy Yogurt Products"(PDF). Food and Nutrition Service (Memorandum). Alexandria, VA: United States Department of Agriculture. Archived from the original(PDF) on 12 July 2017. Retrieved 13 March 2018. The Nutrition Standards in the National School Lunch and School Breakfast Programs final rule was published on January 26, 2012. The final rule gives schools the option to offer commercially prepared tofu as a meat alternate in the National School Lunch Program (NSLP) and School Breakfast Program (SBP).
^Richter, Margrit; Kroke, Anja; Grünewald-Funk, Dorle; Heseker, Helmut; Virmani, Kiran; Watzl, Bernhard (September 2020). "Update to the position of the German Nutrition Society on vegan diets in population groups with special nutritional requirements". Ernährungs Umschau. Deutsche Gesellschaft für Ernährung e. V. (DGE). doi:10.4455/eu.2020.044 (inactive 1 November 2024). Retrieved 2021-04-04. Because the available data remain insufficient, no satisfactory assessment can be made with regard to micronutrient intake and supply status or prevalence of nutrient deficiencies or other adverse health effects regarding a vegan diet in these special population groups.{{cite web}}: CS1 maint: DOI inactive as of November 2024 (link)
^Dobrzańska A, Czerwionka-Szafarska M, Siwińska-Gołębiowska H (2002). "Position of the National Consultant in the Field of Paediatrics and the Team of Experts on the use of vegetarian diets in the developmental age". Stand Med Pediatr. 4: 436–439.
^Pepper, M. Reese; Black, Maureen M. (August 2011). "B12 in fetal development". Seminars in Cell & Developmental Biology. 22 (6): 619–623. doi:10.1016/j.semcdb.2011.05.005. PMID21664980.
^Mangels, Ann Reed; Messina, Virginia (June 2001). "Considerations in planning vegan diets". Journal of the American Dietetic Association. 101 (6): 670–677. doi:10.1016/S0002-8223(01)00169-9. PMID11424546.
^Graham RM, Deery E, Warren MJ (2009). "Vitamin B12: Biosynthesis of the Corrin Ring". In Warren MJ, Smith AG (eds.). Tetrapyrroles Birth, Life and Death. New York, NY: Springer-Verlag. p. 286. doi:10.1007/978-0-387-78518-9_18. ISBN978-0-387-78518-9.
^"Dietary Supplement Fact Sheet: Vitamin B12". National Institutes of Health: Office of Dietary Supplements. Retrieved 2018-02-02. Strict vegetarians and vegans are at greater risk than lacto-ovo vegetarians and nonvegetarians of developing vitamin B12 deficiency because natural food sources of vitamin B12 are limited to animal foods.
^Krajčovičová-Kudláčková, M.; Blažíček, P.; Kopčová, J.; Béderová, A.; Babinská, K. (2000). "Homocysteine Levels in Vegetarians versus Omnivores". Annals of Nutrition and Metabolism. 44 (3): 135–8. doi:10.1159/000012827. PMID11053901. S2CID25418416.
^ abLusas, Edmund W. (2007). "Animal and Vegetable Fats, Oils, and Waxes". Kent and Riegel's Handbook of Industrial Chemistry and Biotechnology. pp. 1549–1656. doi:10.1007/978-0-387-27843-8_34. ISBN978-0-387-27842-1.
^Xia, Wei; Chen, Wei; Peng, Wei-fu; Li, Kun-tai (June 2015). "Industrial vitamin B12 production by Pseudomonas denitrificans using maltose syrup and corn steep liquor as the cost-effective fermentation substrates". Bioprocess and Biosystems Engineering. 38 (6): 1065–1073. doi:10.1007/s00449-014-1348-5. PMID25561346. S2CID42246117.
^Reed Mangels, Virginia Messina, and Mark Messina, "Vitamin B12 (Cobalamin)", The Dietitian's Guide to Vegetarian Diets, Jones & Bartlett Learning, 2011, 181–192.
^"Iodine", Office of Dietary Supplements, National Institutes of Health. The RDA is 110 mcg (0–six months), 130 mcg (7–12 months), 90 mcg (1–8 years), 120 mcg (9–13 years), 150 mcg (14+). The RDA for pregnancy and lactation is 220 and 290 mcg respectively.
^Gerster, H. (1998). "Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)?". International Journal for Vitamin and Nutrition Research. 68 (3): 159–173. PMID9637947.
^Sanders, Thomas A.B. (2009). "DHA status of vegetarians". Prostaglandins, Leukotrienes and Essential Fatty Acids. 81 (2–3): 137–41. doi:10.1016/j.plefa.2009.05.013. PMID19500961.
^Bickelmann, Franziska V.; Leitzmann, Michael F.; Keller, Markus; Baurecht, Hansjörg; Jochem, Carmen (2022-06-06). "Calcium intake in vegan and vegetarian diets: A systematic review and Meta-analysis". Critical Reviews in Food Science and Nutrition. 63 (31): 10659–10677. doi:10.1080/10408398.2022.2084027. ISSN1040-8398. PMID38054787. S2CID249441078.
^Li, Tao; Li, Yanhong; Wu, Shanshan (2021-06-18). "Comparison of human bone mineral densities in subjects on plant-based and omnivorous diets: a systematic review and meta-analysis". Archives of Osteoporosis. 16 (1): 95. doi:10.1007/s11657-021-00955-0. ISSN1862-3514. PMID34145511. S2CID235475271.
^"Iron deficiency—adults". High-risk groups such as vegetarians, adolescent girls and women athletes need to eat iron-rich foods each day (combined with foods that are high in vitamin C). ... Vegetarians who exclude all animal products from their diet may need almost twice as much dietary iron each day as non-vegetarians. Sources include dark green leafy vegetables—such as spinach—and raisins, nuts, seeds, beans, peas, and iron-fortified cereals, breads and pastas
^Hallberg, L; Brune, M; Rossander, L (1989). "The role of vitamin C in iron absorption". International Journal for Vitamin and Nutrition Research. Supplement. 30: 103–8. PMID2507689. The key role of ascorbic acid for the absorption of dietary nonheme iron is generally accepted. The reasons for its action are twofold: (1) the prevention of the formation of insoluble and unabsorbable iron compounds and (2) the reduction of ferric to ferrous iron, which seems to be a requirement for the uptake of iron into the mucosal cells.
^ abMangels, Messina and Messina 2011, 138ff, 143–144. For a detailed discussion, "Iron", Food and Nutrition Board, Institute of Medicine, National Academy Press, 2001, 290–393.
^Haider, Lisa M.; Schwingshackl, Lukas; Hoffmann, Georg; Ekmekcioglu, Cem (2018-05-24). "The effect of vegetarian diets on iron status in adults: A systematic review and meta-analysis". Critical Reviews in Food Science and Nutrition. 58 (8): 1359–1374. doi:10.1080/10408398.2016.1259210. ISSN1549-7852. PMID27880062. S2CID25792199.
^Björn, LO; Wang, T (2000). "Vitamin D in an ecological context". International Journal of Circumpolar Health. 59 (1): 26–32. ISSN1239-9736. PMID10850004.