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, iron, zinc, and iodine. These nutrients may be available in plant foods, with the exception of vitamin B12, which can only be obtained from B12-fortified vegan foods or supplements. Iodine may also require supplementation, such as using iodized salt.
Vitamin B12 deficiency is potentially extremely serious, leading to megaloblastic anemia, nerve degeneration and irreversible neurological damage. Because B12 is stored in large amounts in the liver, deficiency in adults may only begin years after moving to a diet which lacks 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. This is because, unless fortified, plant foods do not contain reliable amounts of active vitamin B12. Vegans are recommended to do one of the following dietary options:
Consume fortified foods 2-3 times per day to get at least 3 micrograms of vitamin B12,
or take 10 micrograms of B12 as a supplement once per day
or take 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.
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. These amounts can be obtained by eating B12 fortified foods, which include some common breakfast cereals, soy 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.
Other B12 fortified foods may include: some almond milks, coconut milks, other plant milks, nutritional yeast, vegan mayonnaise, tofu, and various types and brands of vegan deli slices, burgers, and other veggie meats.
Upon digestion, all protein foods supply amino acids. Varied intake of plant foods can meet human health needs for protein and amino acids. Foods high in protein in a vegan diet include legumes (such as beans and lentils), nuts, seeds, and grains (such as oats, wheat, and quinoa).
Diets without seafood are lower in non-essential long-chain omega-3 fatty acids like DHA and EPA. Short-term supplemental ALA has been shown to increase EPA levels, but not DHA levels, suggesting limited conversion of the intermediary EPA to DHA. DHA supplements derived from DHA-rich microalgae are available, and the human body can also convert DHA to EPA. Although omega-3 has previously been thought useful for helping alleviate dementia, as of 2016[update], there is no good evidence of effectiveness.
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. EPA and DHA supplementation has been shown to reduce platelet aggregation in vegetarians, but a direct link to cardiovascular morbidity and mortality, which is already lower for vegetarians, has yet to be determined.
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.
Many studies have examined possible correlation between veganism, calcium intake, and bone health. The EPIC-Oxford study suggested that vegans who consumed 525 mg or less of calcium per day have an increased risk of bone fractures over meat eaters and vegetarians, but that vegans consuming more than 525 mg/day had a risk of fractures similar to other groups. Overall, the entire group of vegans had a higher risk of fractures. A 2009 study of bone density found the bone density of vegans was 94 percent that of omnivores, but deemed the difference clinically insignificant. Another study in 2009 by the same researchers examined over 100 vegan post-menopausal women, and found that their diet had no adverse effect on bone mineral density (BMD) and no alteration in body composition. Biochemist T. Colin Campbell suggested in The China Study (2005) that osteoporosis is linked to the consumption of animal protein because, unlike plant protein, animal protein increases the acidity of blood and tissues, which he believed was neutralized by calcium pulled from the bones resulting in hypercalciuria. Campbell wrote that his China-Oxford-Cornell study of nutrition in the 1970s and 1980s found that, in rural China, "where the animal to plant ratio [for protein] was about 10 percent, the fracture rate is only one-fifth that of the U.S."
One study reported a "potential danger of iodine deficiency disorders due to strict forms of vegetarian nutrition, especially when fruits and vegetables grown in soils with low [iodine] levels are ingested." 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.
It is recommended for vegans to eat iron-rich foods and vitamin C daily. In several studies, vegans were not found to suffer from iron-deficiency any more than non-vegans. However, 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. Iron supplementation should be taken at different times to other supplements with a 2+ valence (chemistry) such as calcium or magnesium, as they inhibit the absorption of iron.
Due to lack of evidence, no country has published a recommended daily intake for choline, which is a vitamin-like essential nutrient. The Australian, New Zealand, and European Union national nutrition bodies note there have been no reports of choline deficiency in the general population. There are, however, Adequate Intakes such as the European Union's number of 400 mg/day for adults, and the US's number of 425 mg/day for adult non-pregnant women and 550 mg/day for adult men.
Choline deficiency, as created in lab conditions, can lead to health problems such as liver damage, a result of liver cells initiating programmed cell death (apoptosis), as well as an increase in neural tube defects in pregnant women. In a study, 77% of men, 44% of premenopausal women, and 80% of postmenopausal women developed fatty liver or muscle damage due to choline deficiency, showing that subject characteristics regulate the dietary requirement. There is also some evidence that choline is an anti-inflammatory as well, but further studies are needed to confirm/refute findings. It is worth noting that many multivitamins do not contain the Adequate Intake of choline.
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), brussel sprouts (63 mg/cup), and broccoli (62 mg/cup) are also good sources of choline. Other sources include soy lecithin, cauliflower, spinach, wheat germ, firm tofu, kidney beans, quinoa and amaranth.
The main function of vitamin D in the body is increased absorption of calcium, therefore it is good for the bones. It also connects with receptors in the prostate, the heart, blood vessels, muscles, endocrine glands and others. 
Sunlight, fortified foods, and supplements, are the main sources of vitamin D for vegans. Humans produce vitamin D naturally in response to ultraviolet light (UV). Complete cloud cover reduces UV penetration by up to 50%, and outdoor shade reduces UV penetration by 60%. UV light penetrates the skin at wavelengths between 290 and 320 nanometers, where it is then converted into vitamin D3.  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.
Although vitamin D3 is produced in small amounts by lichens or algae exposed to sunlight, industrial production in commercial quantities is limited, and there are few supplement products as of 2019.
The recommended daily allowance in vitamin D for adults under the age of 70 years old is between 600 and 4,000 IU, and for adults over 70 years old, 800 to 4,000 IU. 
Reports on exactly how much vitamin D is produced by exposure to sunlight are wild and varied, across the board.
^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."
^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.
^Appleby, P; Roddam, A; Allen, N; Key, T (2007). "Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford". European Journal of Clinical Nutrition. 61 (12): 1400–6. doi:10.1038/sj.ejcn.1602659. PMID17299475.
^Ho-Pham, L. T; Nguyen, N. D; Nguyen, T. V (2009). "Effect of vegetarian diets on bone mineral density: A Bayesian meta-analysis". American Journal of Clinical Nutrition. 90 (4): 943–50. doi:10.3945/ajcn.2009.27521. PMID19571226.
^Ho-Pham, L. T.; Nguyen, P. L. T.; Le, T. T. T.; Doan, T. A. T.; Tran, N. T.; Le, T. A.; Nguyen, T. V. (2009). "Veganism, bone mineral density, and body composition: A study in Buddhist nuns". Osteoporosis International. 20 (12): 2087–93. doi:10.1007/s00198-009-0916-z. PMID19350341.
^Junshi, Chen; Campbell, T. Colin; Li; et al., eds. (1990). Diet, lifestyle, and mortality in China: a study of the characteristics of 65 Chinese counties. Oxford University Press. ISBN978-0-19-261843-6.[page needed]
^Remer, Thomas; Neubert, Annette; Manz, Friedrich (1999). "Increased risk of iodine deficiency with vegetarian nutrition". British Journal of Nutrition. 81 (1): 45–9. doi:10.1017/s0007114599000136. PMID10341675.
^"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
^Larsson, CL; Johansson, GK (2002). "Dietary intake and nutritional status of young vegans and omnivores in Sweden". The American Journal of Clinical Nutrition. 76 (1): 100–6. doi:10.1093/ajcn/76.1.100. PMID12081822.
^Messina, MJ; Messina, VL (1996). The Dietitian's Guide to Vegetarian Diets: Issues and Applications. Gaithersburg, MD: Aspen Publishers.[page needed]
^Ball, MJ; Bartlett, MA (1999). "Dietary intake and iron status of Australian vegetarian women". The American Journal of Clinical Nutrition. 70 (3): 353–8. doi:10.1093/ajcn/70.3.353. PMID10479197.
^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.
^Nutrient Reference Values for Australia and New Zealand, Although choline is essential, there appear to have been no reports of deficiency in the general population. Deficiencies have been seen in experimental situations and also in total parenteral nutrition (Buchman et al. 1992, 1993, 1995, Chalwa et al. 1989, Shapira et al. 1986, Sheard et al. 1986).
^"Choline". Office of Dietary Supplements, US National Institutes of Health. 26 September 2018. Retrieved 26 January 2019.
^ abHigdon, Jane (Nov 2003). "Choline". Linus Pauling Institute at Oregon State University. Retrieved 3 March 2014.